Visible Light-Promoted Formation of C–B and C–S Bonds under Metal- and Photocatalyst-Free Conditions

Published as part of the 50 Years SYNTHESIS – Golden Anniversary Issue

Abstract

A green, efficient, photoinduced synthesis of arylboronic esters and aryl sulfides has been developed. Bench stable arylazo sulfones were used as radical precursors for a photocatalyst- and additive-free carbon–heteroatom bond formation under visible light. The protocols are applicable to a wide range of substrates, providing products in good yields.

Key words

arylazo sulfones - aryl radicals - arylboronic esters - aryl sulfides

The development of mild and sustainable protocols for carbon–heteroatom bond formation has received an impressive attention in recent years. Indeed, aryl boronates and aryl sulfides play a key role in organic synthesis,[1] catalysis,[2] material science,[3] and especially medicinal chemistry.[4] Many natural products, drugs, and crop-protection substances bear sulfur-containing functional groups.[5] In addition, since the introduction of Bortezomib in 2003 by the FDA (US Federal Drug Administration)[6] for treating multiple myeloma, an increasing interest in boronic acids as drug candidates has developed.[7]

Classical methods for the generation of carbon–heteroatom bonds involve thermal reactions with organometal derivatives,[8] the use of transition-metal catalysts in combination with expensive often air-sensitive ligands, strong bases, and additives in excess amounts.[9] In order to reduce costs and contaminations with heavy metals, the development of more efficient and environmentally friendly alternative routes is highly desirable.

Several metal-free photoinduced borylation protocols of haloarenes,[10] quaternary arylammonium salts, aryl triflates,[11] and carboxylic acids[12] as substrates have been published recently (Scheme [1, a–c]). Such methods feature the advantage of avoiding the use of late transition metals. Nevertheless, they still suffer from several drawbacks, like the need of ultraviolet light irradiation and additives such as NaI, N,N,N′,N′-tetramethyldiaminomethane (TMDAM), or Cs₂CO₃ in stochiometric amounts. An alternative for the preparation of arylboronic esters and aryl sulfides under photochemical conditions, takes advantage of aryl halides and aryldiazonium salts (Scheme [1, d–f]),[13] which are widely used as aryl radical sources in photochemistry. The activation of aryldiazonium salts under visible light requires a photocatalyst (PC), since the aryl radical can only be formed by single-electron transfer (SET) from the excited state of the photocatalyst to the diazonium salt.

Scheme 1 Representative methods for the synthesis of arylboronic ­esters and aryl sulfides

Recently published protocols revealed that arylazo sulfones can be successfully used in the metal-free arylation of heterocycles and unactivated arenes without the need of additives.[14] Herein, we report the application of arylazo sulfones in the photocatalyst-, metal- and additive-free, visible-light-driven synthesis of aryl sulfides and aryl boronates.[15]

The present protocol is a sustainable approach that exploit bench stable arylazo sulfones, easily prepared from anilines, and allow the wavelength selective generation of aryl radicals and aryl cations.[14] [15]

Table 1 Reaction Optimization for the Photocatalyst-Free Aryl ­Borylation^a

Entry	Additive	Light source	Yield (%)
1	NaI/TMDAM	in the dark	–
2	NaI/TMDAM	daylight	–
3	NaI/TMDAM	blue LEDs 12 W	traces
4	NaI/TMDAM	blue LEDs 24 W	59
5	–	blue LEDs 24 W	56
6	NaI/TMDAM	Kessil lamp 34 W	79
7	–	Kessil lamp 34 W	78
8b	–	Kessil lamp 34 W	59
9c,d	–	Kessil lamp 34 W	61

^a Reaction conditions: 1f (0.1 mmol), 2a (0.2 mmol), NaI (50 mol%), ­TMDAM (1 equiv), MeCN, r.t., 12 h, yield after purification by column ­chromatography.

^b Reaction was carried out in MeOH.

^c Reaction was carried out in MeCN/H₂O (9:1).

^d Yield, determined via ¹H NMR spectroscopy using dimethyl sulfone as internal standard.

At the beginning of our studies, several reaction conditions were evaluated in order to determine the ideal setup for the photocatalyst-free borylation of arylazo sulfones (Table [1]). Initially, a solution of arylazo sulfone 1f, bis(pinacolato)diboron [B(pin)₂, 2a], with NaI and TMDAM as additives in acetonitrile was stirred at room temperature. No product formation was observed neither in the absence of light (Table [1], entry 1) nor when exposing the solution to daylight (entry 2). Only traces of the aryl-B(pin) 3f were obtained using 12 W LEDs for 12 hours (entry 3). However, 3f was isolated in 59% yield using high power 24 W blue LEDs (entry 4). Also, the H150 blue Kessil lamp (34 W) was tested for irradiation, increasing the yield up to 79% (entry 6). Reactions without NaI and TMDAM showed that there is no need for additives to form the aryl boronate 3f in 56% yield, when using high power blue LEDs (entry 5). The yield was further improved to 78% by using a blue 34 W Kessil lamp (entry 7). Other polar solvents like methanol and an acetonitrile/water mixture (9:1) gave no improvement on the yield (entries 8 and 9). The best results were obtained in acetonitrile using 34 W blue light lamp for irradiation (­entry 7).

Based on the optimised conditions, the substrate scope was examined using different arylazo sulfones and borylating agents (Scheme [2]). We were pleased to see that the photoinduced aryl borylation tolerates the presence of halides (3b–e), electron-donating (3f–g), and electron-withdrawing substituents (3h–o) on the aromatic moiety of the arylazo sulfones. In all cases, moderate to good yields were achieved (up to 78%). In addition, substrates containing potentially light-reactive substituents such as aryl ketone (3h) and biaryl (3i) were also appropriate radical precursors to give the resulting product under the described reaction conditions. Gratifyingly, arylazo sulfones bearing a bromide and iodide as substituent underwent also borylation (3d and 3e), without cleavage of the carbon–halogen bond.

Scheme 2 Substrate scope of the photoinduced aryl borylation. Reagents and conditions: 1 (0.1 mmol), 2 (0.2 mmol), MeCN, r.t., H150 Kessil lamp (blue light 34 W), 12 h; yields after purification by column chromatography. ^a Yield determined via ¹H NMR using dimethyl sulfone as internal standard, confirmed by MS (EI): m/z = 230 (87).

Next, different borylating agents were studied. The results showed that compared to B₂pin₂ (2a), bis(neopentyl glycolato)diboron (2b), and bis(hexylene glycolato)diboron (2c) gave slightly lower yields for the respective products 3p (64%) and 3q (56%). The borylation of 4-chlorophenylazo sulfone using bis(catecholato)diboron (2d) was also feasible.

We thus extended our investigation to the synthesis of thioethers, the visible light-mediated thiolation of arylazo sulfones was approached in the presence of disulfides as the thiolating reagent (Scheme [3]). The scope was evaluated by employing various arylazo sulfones bearing halides, cyano, nitro, pentafluorosulfide, and keto groups (5a–j). The products were obtained in moderate to good yields. Additionally, different ortho- and meta-substituents were tolerated (5k–m). Diethyl sulfide (4b) and diphenyl sulfide (4c) were also successful in the photocatalyst-free thioether synthesis leading to 5n and 5o in 50% and 46% yield, respectively.

Scheme 3 Substrate scope of the photoinduced synthesis of aryl sulfides. Reagents and conditions: 1 (0.2 mmol), 4 (0.4 mmol), MeCN, r.t., H150 Kessil lamp (blue light 34 W), 12 h. Yields after purification by column chromatography.

The proposed mechanism for the synthesis of aryl sulfides and boronates is depicted in Scheme [4]. Irradiation of 1 with blue light (λ = 420 nm) leads to the excited ¹nπ*-state 1* (path a). Subsequent homolytic cleavage of the S–N bond (path b) affords the aryl radical 6 and methanesulfonyl radical 7.[14] Such radicals are trapped by the diboron/disulfide (Y–Y) reagent 2 to give products 3 or 5 and the boron/sulfide radical (Y^•) 8 (path c and f). The combination between aryl and X-radicals to form 3 or 5 is also possible (path d). Hydrogen atom abstraction by the generated radicals from the solvent to give arenes 9 and sulfinic acid (10) could also take place as a secondary path (path g). Finally, the recombination of the aryl 6 and methanesulfonyl radical 7 leads to a second possible by-product sulfone 12 (path e, see SI).

Scheme 4 Proposed mechanism for the PC-free photoinduced borylation and aryl sulfide formation via arylazo sulfones as stable radical precursors

In summary, we have developed an efficient, green, photoinduced aryl borylation and aryl thioether formation protocol with arylazo sulfones as aryl radical precursors. These stable and easy to handle aryldiazonium salt derivatives show a high photoreactivity under blue light irradiation. The scope of the borylation reaction includes both, different aryl derivatives and different diboron esters, providing products in moderate to good yields. In addition, this simple approach could also be transferred to the aryl sulfide synthesis with disulfides.

Unless otherwise noted, all reagents were obtained from commercial suppliers. Organic solvents were purified from by solvent purification system MBraun SPS-5 and stored over molecular sieves under argon. Diazonium salts were synthesised by following a known procedure[16] and purified by recrystallisation from acetone/Et₂O. For irradiation of the reaction mixtures, different light sources were used: a) blue LED stripes (12W, 24 W) and b) H150 Kessil lamp (34 W, λ = 420 nm). The reaction was cooled using a small ventilator, placed at 3 cm from the reaction vessels. A shield covered with aluminum foil was placed in front of the reaction setup to protect eyes from light irradiation. Solvents for chromatography were technical grade and distilled prior to use. TLC was carried out on Merck aluminum support plates Silica gel 60 F₂₅₄. Visualisation was achieved under a UV mineral light or stained using cer-molybdato phosphoric acid (CAM). Column chromatography was performed using silica gel Merck 60 (0.2–0.063 mm). ¹H NMR spectra were recorded on Varian 400 MHz and 600 MHz spectrometers at 400 and 600 MHz. ¹³C NMR spectra were similarly recorded at 100 or 150 MHz, using a broadband decoupled mode. ¹¹B NMR spectra were measured at 128 MHz and ¹⁹F NMR measurements were performed at 376 MHz on Varian 400 MHz and Mercury 300 MHz spectrometers, respectively. NMR chemical shifts (δ) are reported in parts per million (ppm) relative to residual proton signals in CDCl₃ (δ = 7.26, 77.16 ppm). Coupling constants (J) are reported in hertz (Hz) and refer to apparent multiplicities. Standard abbreviations are used for the multiplicities. Mass spectra (EI-MS, 70 eV) were conducted on a Finnigan SSQ 7000 spectrometer. HRMS were recorded on a Thermo Scientific TQ Orbitrap XI spectrometer. IR spectra were recorded on an Jasco FT/IR-420 spectrophotometer and are reported in terms of frequency of absorption (cm^–1).

Synthesis of Arylazosulfones 1;[14a] General Procedure

To a cooled (0 °C) suspension of the appropriative diazonium salt (1.00 equiv, 0.30 M) in anhyd CH₂Cl₂ was added MeSO₂Na (1.00 equiv) in one portion. The temperature was allowed to rise to r.t. overnight. The resulting mixture was filtered, and the obtained solution evaporated. The crude solid was purified by either dissolving in cold CH₂Cl₂ and precipitation by adding n-hexane or column chromatography.

1-(Methylsulfonyl)-2-(phenyl)diazene (1a)

Reaction of benzenediazonium tetrafluoroborate (300 mg, 1.56 mmol) and MeSO₂Na (160 mg, 1.56 mmol, 1.00 equiv) in CH₂Cl₂ (5.00 mL, 0.3 M) gave 1a (185 mg, 9.93·10^–1 mmol, 65%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.95 (dd, J = 8.4, 1.1 Hz, 2 H), 7.70–7.65 (m, 1 H), 7.58 (t, J = 7.6 Hz, 2 H), 3.23 (d, J = 3.3 Hz, 3 H).

The NMR data were in accordance with the literature.[14a]

1-(Methylsulfonyl)-2-(4-fluorophenyl)diazene (1b)

Reaction of 4-fluorobenzenediazonium tetrafluoroborate (300 mg, 1.43 mmol) and MeSO₂Na (146 mg, 1.43 mmol, 1.00 equiv) in CH₂Cl₂ (5.00 mL, 0.30 M) gave 1b (197 mg, 9.76·10^–1 mmol, 68%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid; mp 66.7–67.0 °C (dec.).

IR (KBr, neat): 3025, 2942, 1587, 1492, 1332, 1227, 1137, 954, 892, 851 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 7.99 (ddd, J = 8.2, 5.1, 2.6 Hz, 2 H), 7.31–7.19 (m, 2 H), 3.20 (d, J = 7.2 Hz, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 165.5, 145.5, 127.2, 116.9, 34.8.

¹⁹F NMR (376 MHz, CDCl₃): δ = –101.0.

MS (EI): m/z (%) = 123 (27), 95 (100).

1-(Methylsulfonyl)-2-(4-Chlorophenyl)diazene (1c)

Reaction of 4-chlorobenzenediazonium tetrafluoroborate (1.20 g, 5.30 mmol) and MeSO₂Na (541 mg, 5.30 mmol, 1.00 equiv) in CH₂Cl₂ (17.5 mL, 0.30 M) gave 1c (584 mg, 2.67 mmol, 51%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.91 (d, J = 8.6 Hz, 2 H), 7.56 (d, J = 8.6 Hz, 2 H), 3.22 (s, 3 H).

The NMR data were in accordance with the literature.[14a]

1-(Methylsulfonyl)-2-(4-Bromophenyl)diazene (1d)

Reaction of 4-bromobenzenediazonium tetrafluoroborate (1.00 g, 3.69 mmol) and MeSO₂Na (377 mg, 3.69 mmol, 1.00 equiv) in CH₂Cl₂ (12.3 mL, 0.30 M) gave 1d (533 mg, 2.03 mmol, 55%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.83 (d, J = 8.7 Hz, 2 H), 7.73 (d, J = 8.7 Hz, 2 H), 3.22 (s, 3 H).

The NMR data were in accordance with the literature.[14b]

1-(Methylsulfonyl)-2-(4-Iodophenyl)diazene (1e)

Reaction of 4-iodobenzenediazonium tetrafluoroborate (497 mg, 1.56 mmol) and MeSO₂Na (160 mg, 1.56 mmol, 1.00 equiv) in CH₂Cl₂ (5.20 mL, 0.30 M) gave 1e (212 mg, 6.85·10^–1 mmol, 44%) after recrystallisation from cold CH₂Cl₂/n-hexane) as an orange solid; mp 132.0–132.4 °C (dec.).

IR (KBr, neat): 3037, 2928, 2074, 1474, 1316, 1139, 952, 887, 830 cm^–1.

¹H NMR (600·MHz, CDCl₃): δ = 7.95 (d, J = 8.6 Hz, 2 H), 7.65 (d, J = 8.6 Hz, 2 H), 3.22 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 148.2, 139.2, 125.6, 103.6, 34.8.

MS (EI): m/z (%) = 76 (75), 203 (100), 231 (47).

1-(Methylsulfonyl)-2-(4-Methylphenyl)diazene (1f)

Reaction of 4-methylbenzenediazonium tetrafluoroborate (225 mg, 1.09 mmol) and MeSO₂Na (112 mg, 1.09 mmol, 1.00 equiv) in CH₂Cl₂ (3.60 mL, 0.30 M) gave 1f (75.4 mg, 3.80·10^–1 mmol, 35%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid; mp 100.2–100.9 °C (dec.).

IR (KBr, neat): 3043, 2937, 3390, 2073, 1324, 1146, 948, 893, 826 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 7.85 (d, J = 8.3 Hz, 2 H), 7.37 (d, J = 8.2 Hz, 2 H), 3.21 (s, 3 H), 2.48 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 146.9, 130.3, 124.7, 34.7, 21.9.

MS (EI): m/z (%) = 65 (39), 91 (100), 119 (27).

1-(Methylsulfonyl)-2-(4-Methoxyphenyl)diazene (1g)

Reaction of 4-methoxybenzenediazonium tetrafluoroborate (225 mg, 1.01 mmol) and MeSO₂Na (103 mg, 1.01 mmol, 1.00 equiv) in CH₂Cl₂ (3.40 mL, 0.30 M) gave 1g (143 mg, 6.67·10^–1 mmol, 66%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.95 (d, J = 9.0 Hz, 2 H), 7.04 (d, J = 9.0 Hz, 2 H), 3.94 (s, 3 H), 3.19 (s, 3 H).

The NMR data were in accordance with the literature.[14a]

1-(Methylsulfonyl)-2-(4-Acetylphenyl)diazene (1h)

Reaction of 4-acetylbenzenediazonium tetrafluoroborate (1.00 g, 4.27 mmol) and MeSO₂Na (437 mg, 4.27 mmol, 1.00 equiv) in CH₂Cl₂ (14.0 mL, 0.30 M) gave 1h (840 mg, 3.71 mmol, 87%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 8.15 (d, J = 8.5 Hz, 2 H), 8.03 (d, J = 8.5 Hz, 2 H), 3.26 (s, 3 H), 2.69 (s, 3 H).

The NMR data were in accordance with the literature.[14a]

1-(Methylsulfonyl)-2-(1,1′biphenyl)diazene (1i)

Reaction of 1,1′-biphenyldiazonium tetrafluoroborate (338 mg, 1.43 mmol) and MeSO₂Na (146 mg, 1.43 mmol, 1.00 equiv) in CH₂Cl₂ (5.00 mL, 0.30 M) gave 1i (223 mg, 8.58·10^–1 mmol, 60%) after recrystallisation from cold CH₂Cl₂/n-hexane as an orange solid; mp 115.5–115.9 °C (dec.).

IR (KBr, neat): 3038, 2932, 2263, 2062, 1482, 1328, 1142, 953, 889, 848, 767, 690 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 8.03 (d, J = 8.5 Hz, 2 H), 7.81 (d, J = 8.5 Hz, 2 H), 7.67 (d, J = 7.5 Hz, 2 H), 7.51 (t, J = 7.6 Hz, 2 H), 7.45 (t, J = 7.3 Hz, 1 H), 3.24 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 148.8, 148.0, 139.0, 129.1, 128.8, 128.2, 127.3, 125.2, 34.8.

MS (EI): m/z (%) = 181 (22), 153 (100).

1-(Methylsulfonyl)-2-(4-nitrophenyl)diazene (1j)

Reaction of 4-nitrobenzenediazonium tetrafluoroborate (304 mg, 1.28 mmol) and MeSO₂Na (131 mg, 1.28 mmol, 1.00 equiv) in CH₂Cl₂ (4.30 mL, 0.30 M) gave 1j (215 mg, 9.38·10^–1 mmol, 71%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 8.45 (d, J = 9.0 Hz, 2 H), 8.12 (d, J = 8.9 Hz, 2 H), 3.28 (s, 3 H).

The NMR data were in accordance with the literature.[14b]

1-(Methylsulfonyl)-2-[4-pentafluorosulfanyl)phenyl]diazene (1k)

Reaction of 4-(pentafluorosulfanyl)benzenediazonium tetrafluoroborate (497 mg, 1.56 mmol) and MeSO₂Na (160 mg, 1.56 mmol, 1.00 equiv) in CH₂Cl₂ (5.30 mL, 0.30 M) gave 1k (281 mg, 9.06·10^–1 mmol, 58%) after recrystallisation from cold CH₂Cl₂/n-hexane as an orange solid; mp 100.4–100.9 °C (dec.).

IR (KBr, neat): 3019, 2934, 1323, 1142, 963, 825 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.07–7.92 (m, 4 H), 3.24 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃): δ = 149.8, 127.7, 124.4, 34.9.

¹⁹F NMR (376 MHz, CDCl₃): δ = 83.35–79.34 (m), 62.52 (d, J = 150.5 Hz).

MS (EI): m/z (%) = 231 (35), 203 (100), 95 (69), 75 (61).

1-(Methylsulfonyl)-2-(4-cyanophenyl)diazene (1l)

Reaction of 4-cyanobenzenediazonium tetrafluoroborate (278 mg, 1.28 mmol) and MeSO₂Na (131 mg, 1.28 mmol, 1.00 equiv) in CH₂Cl₂ (4.30 mL, 0.30 M) gave 1l (230 mg, 1.10 mmol, 86%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 8.05 (d, J = 8.5 Hz, 2 H), 7.90 (d, J = 8.6 Hz, 2 H), 3.26 (s, 3 H).

The NMR data were in accordance with the literature.[14b]

1-(Methylsulfonyl)-2-(4-ethoxycarbonylphenyl)diazene (1m)

Reaction of 4-ethoxycarbonylbenzediazonium tetrafluoroborate (431 mg, 1.56 mmol) and MeSO₂Na (160 mg, 1.56 mmol, 1.00 equiv) in CH₂Cl₂ (5.30 mL, 0.30 M) gave 1m (265 mg, 1.03 mmol, 66%) after column chromatography on silica gel (eluent: 3:1 pentane/EtOAc), followed by recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid; mp 104.6–105.0 °C (dec.).

IR (KBr, neat): 3016, 2988, 2935, 2901, 1717, 1334, 1272, 1148, 1102, 1015, 960, 895, 867, 770 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 8.25 (d, J = 8.5 Hz, 2 H), 8.00 (d, J = 8.4 Hz, 2 H), 4.43 (q, J = 7.1 Hz, 2 H), 3.25 (s, 3 H), 1.43 (t, J = 7.1 Hz, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 165.1, 151.1, 130.9, 124.2, 61.8, 34.8, 14.2.

MS (EI): m/z (%) = 177 (100), 149 (11).

1-(Methylsulfonyl)-2-(4-methoxycarbonylphenyl)diazene (1n)

Reaction of 4-methoxycarbonylbenzediazonium tetrafluoroborate (391 mg, 1.56 mmol) and MeSO₂Na (160 mg, 1.56 mmol, 1.00 equiv) in CH₂Cl₂ (5.30 mL, 0.30 M) gave 1n (293 mg, 1.21 mmol, 78%) after column chromatography on silica gel (eluent: 3:1 pentane/EtOAc), followed by recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid; mp 113.0–113.5 °C (dec.).

IR (KBr, neat): 3016, 2935, 1713, 1435, 1331, 1282, 1155, 1105, 897, 865, 773, 689 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 8.24 (d, J = 8.5 Hz, 2 H), 8.00 (d, J = 8.5 Hz, 2 H), 3.98 (s, 3 H), 3.25 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 165.6, 151.2, 135.5, 130.9, 124.2, 52.7, 34.8.

MS (EI): m/z (%) = 163 (90), 135 (100), 103 (37).

1-(Methylsulfonyl)-2-(α-naphthalene)diazene (1o)

Reaction of α-naphthalenediazonium tetrafluoroborate (315 mg, 1.30 mmol) and MeSO₂Na (133 mg, 1.30 mmol, 1.00 equiv) in CH₂Cl₂ (4.30 mL, 0.30 M) gave 1o (286 mg, 1.22 mmol, 91%) after recrystallisation from cold CH₂Cl₂/n-hexane as an orange solid; mp 133.1–133.5 °C (dec.).

IR (KBr, neat): 3042, 2936, 2074, 1326, 1147, 1087, 1147, 955, 981, 851, 806, 763 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 8.68 (d, J = 8.4 Hz, 1 H), 8.18 (t, J = 14.9 Hz, 1 H), 8.03–7.95 (m, 2 H), 7.73 (dd, J = 18.1, 10.4 Hz, 1 H), 7.64 (dt, J = 22.0, 7.9 Hz, 2 H), 3.34 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 143.9, 136.3, 134.3, 131.4, 128.6, 128.4, 127.3, 125.3, 122.5, 115.1, 35.1.

MS (EI): m/z (%) = 155 (100), 143 (76), 127 (28).

1-(Methylsulfonyl)-2-(2-Cyanophenyl)diazene (1p)

Reaction of 2-cyanobenzenediazonium tetrafluoroborate (100 mg 4.61·10^–1 mmol) and MeSO₂Na (46.7 mg, 4.61·10^–1 mmol, 1.00 equiv) in CH₂Cl₂ (1.50 mL, 0.30 M) gave 1p (38.0 mg, 1.82·10^–1 mmol, 40%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid; mp 112.1–112.7 °C (dec.).

IR (KBr, neat): 3455, 3149, 3098, 3036, 3010, 2926, 2852, 2633, 2491, 2339, 2231, 2089, 1989, 1870, 1440, 1647, 1550, 1485, 1421, 1334, 1273, 1209, 1151, 1039, 956, 887, 810, 773, 746, 694 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 7.99–7.88 (m, 2 H), 7.85–7.78 (m, 2 H), 3.29 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 149.1, 135.1, 134.1, 133.9, 117.2, 116.0, 115.2, 34.6.

MS (EI): m/z (%) = 102 (100), 130 (53).

Methyl 2-[(Methylsulfonyl)diazenyl]benzoate (1q)

Reaction of 2-methoxycarbonylbenzenediazonium tetrafluoroborate (100 mg, 0.40 mmol) and MeSO₂Na (40.9 mg, 0.40 mmol, 1.00 equiv) in CH₂Cl₂ (1.50 mL, 0.30 M) gave 1q (60.7 mg, 2.51·10^–1 mmol, 63%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid; mp 78.8–79.2 °C (dec.).

IR (KBr, neat): 3436, 3101, 3019, 2940, 2848, 2638, 2281, 2163, 2096, 1719, 1586, 1489, 1441, 1319, 1267, 1199, 1141, 1267, 1199, 1141, 1077, 958, 889, 833, 765, 701 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 7.99 (dd, J = 7.2, 1.8 Hz, 1 H), 7.75–7.64 (m, 2 H), 7.61 (dd, J = 7.5, 1.5 Hz, 1 H), 3.94 (s, 3 H), 3.21 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 165.7, 147.9, 133.5, 132.7, 130.8, 130.4, 117.5, 52.8.

MS (EI): m/z (%) = 163 (26), 135 (100).

1-(Methylsulfonyl)-2-(3-nitrophenyl)diazene (1r)

Reaction of 3-nitrobenzenediazonium tetrafluoroborate (100 mg, 0.42 mmol) and MeSO₂Na (42.4 mg, 0.42 mmol, 1.00 equiv) in CH₂Cl₂ (1.50 mL, 0.30 M) gave 1r (38.6 mg, 1.82·10^–1 mmol, 40%) after recrystallisation from cold CH₂Cl₂/n-hexane as a yellow solid; mp 120.9–121.4 °C (dec.).

IR (KBr, neat): 3086, 3019, 2935, 2875, 2652, 2323, 2165, 2113, 1996, 1969, 1931, 1827, 1755, 1605, 1525, 1330, 1154, 1084, 1002, 957, 918, 869, 817, 790, 728, 667 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 8.78 (t, J = 2.0 Hz, 1 H), 8.53 (ddd, J = 8.2, 2.2, 1.0 Hz, 1 H), 8.33–8.24 (m, 1 H), 7.83 (t, J = 8.1 Hz, 1 H), 3.29 (s, 3 H).

¹³C NMR (151 MHz, CDCl₃): δ = 149.2, 130.8, 129.3, 119.4, 35.1.

MS (EI): m/z (%) = 122 (100), 151 (53).

Photoinduced Arylborylation; General Procedure

A solution of arylazo sulfone 1 (0.10 mmol) and the respective diboron 2 (0.20 mmol, 2.00 equiv) in degassed MeCN (2.00 mL, 0.05 M) was poured into a glass vessel, capped, and exposed to blue light (H150 Kessil lamp, 34 W, 420 nm) at r.t. for 12 h. After the completion of the reaction (detected by TLC), the solvent was removed in vacuo and the crude product was purified via column chromatography on silica gel.

4,4,5,5-Tetramethyl-2-phenyl-1,3,2-dioxaborolane (3a)

Reaction of 1a (18.4 mg, 0.10 mmol) and bis(pinacolato)diboron (2a; 50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3a (10.8 mg, 5.29·10^–2 mmol, 53%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.81 (d, J = 7.0 Hz, 2 H), 7.46 (t, J = 7.4 Hz, 1 H), 7.37 (t, J = 7.5 Hz, 2 H), 1.35 (s, J = 4.6 Hz, 12 H).

The NMR data were in accordance with the literature.[10b]

2-(4-Fluorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3b)

Reaction of 1b (20.2 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3b (11.9 mg, 5.36·10^–2 mmol, 54%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.66 (d, J = 8.0 Hz, 2 H), 7.50 (d, J = 8.1 Hz, 2 H), 1.34 (s, 12 H).

The NMR data were in accordance with the literature.[17]

2-(4-Chlorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3c)

Reaction of 1c (21.9 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3c (16.4 mg, 6.88·10^–2 mmol, 69%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.73 (d, J = 8.0 Hz, 2 H), 7.34 (d, J = 8.0 Hz, 2 H), 1.34 (s, 12 H).

The NMR data were in accordance with the literature.[17]

2-(4-Bromophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3d)

Reaction of 1d (26.3 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3d (16.9 mg, 5.97·10^–2 mmol, 60%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a white solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.80 (t, J = 7.2 Hz, 2 H), 7.05 (t, J = 8.8 Hz, 2 H), 1.35 (d, J = 8.5 Hz, 12 H).

The NMR data were in accordance with the literature.[17]

2-(4-Iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3e)

Reaction of 1e (26.3 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3e (16.9 mg, 5.12·10^–2 mmol, 51%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.72 (d, J = 8.0 Hz, 2 H), 7.51 (d, J = 7.9 Hz, 2 H), 1.33 (s, 12 H).

The NMR data were in accordance with the literature.[17]

2-(4-Methylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3f)

Reaction of 1f (19.8 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3f (17.0 mg, 7.79·10^–2 mmol, 78%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.71 (d, J = 7.8 Hz, 2 H), 7.17 (dd, J = 19.6, 6.9 Hz, 2 H), 2.37 (s, 3 H), 1.34 (s, 12 H).

The NMR data were in accordance with the literature.[10b]

2-(4-Methoxyphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3g)

Reaction of 4-methylphenyl mesylate (1g, 21.4 mg, 0.10 mmol) and bis(pinacolato)diboron (2a, 50.8 mg, 0.20 mmol, 2.00 equiv) in acetonitrile (2.00 mL, 0.05 M) gave 3g (15.7 mg, 6.71·10^-2 mmol, 67%) after purification via column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.73 (d, J = 8.4 Hz, 2 H), 6.90 (d, J = 8.5 Hz, 2 H), 3.83 (s, 3 H), 1.33 (s, 12 H) ppm.

The NMR data were in accordance with the reported literature.[10a]

2-(4-Acetylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3h)

Reaction of 1h (22.6 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3h (12.8 mg, 5.20·10^–2 mmol, 52%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a white solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.91 (m, 4 H), 2.62 (s, 3 H), 1.36 (s, J = 7.3 Hz, 12 H).

The NMR data were in accordance with the literature.[10a]

2-(1,1′-Biphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3i)

Reaction of 1i (26.0 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3i (15.9 mg, 5.68·10^–2 mmol, 57%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.90 (d, J = 8.0 Hz, 2 H), 7.62 (dt, J = 11.4, 5.3 Hz, 4 H), 7.45 (t, J = 7.7 Hz, 2 H), 7.38–7.34 (m, 1 H), 1.37 (s, 12 H).

The NMR data were in accordance with the literature.[10a]

2-(4-Nitrophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3j)

Reaction of 1j (22.9 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3j (13.4 mg, 5.38·10^–2 mmol, 54%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.88 (d, J = 8.1 Hz, 2 H), 7.73 (d, J = 8.5 Hz, 2 H), 1.35 (s, 12 H).

The NMR data were in accordance with the literature.[18]

2-[4-Pentafluorosulfanyl)phenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3k)

Reaction of 1k (31.0 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3k (20.8 mg, 6.30·10^–2 mmol, 63%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a yellowish solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.88 (d, J = 8.1 Hz, 2 H), 7.73 (d, J = 8.5 Hz, 2 H), 1.35 (s, 12 H).

The NMR data were in accordance with the literature.[19]

2-(4-Nitrophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3l)

Reaction of 1l (20.9 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3l (10.3 mg, 4.50·10^–2 mmol, 45%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.88 (d, J = 7.9 Hz, 2 H), 7.64 (d, J = 8.0 Hz, 2 H), 1.35 (s, 12 H).

The NMR data were in accordance with the literature.[10a]

Ethyl 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benzoate (3m)

Reaction of 1m (25.6 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3m (15.2 mg, 5.50·10^–2 mmol, 55%) after purification via column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a white solid.

¹H NMR (600 MHz, CDCl₃): δ = 8.02 (d, J = 8.0 Hz, 2 H), 7.86 (d, J = 7.9 Hz, 2 H), 4.38 (q, J = 7.1 Hz, 2 H), 1.40 (t, J = 7.1 Hz, 3 H), 1.36 (s, 12 H).

The NMR data were in accordance with the literature.[10a]

Methyl 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benzoate (3n)

Reaction of 1n (24.2 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3n (14.8 mg, 5.68·10^–2 mmol, 57%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (30:1) as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 8.02 (d, J = 8.1 Hz, 2 H), 7.87 (d, J = 8.1 Hz, 2 H), 3.92 (s, 3 H), 1.35 (s, 12 H).

The NMR data were in accordance with the literature.[17]

2-(Naphthalene-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3o)

Reaction of 1o (23.4 mg, 0.10 mmol) and 2a (50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3o (13.3 mg, 5.23·10^–2 mmol, 52%) after purification by column chromatography on silica gel with a mixture of toluene/EtOAc (50:1) as a yellowish solid.

¹H NMR (600 MHz, CDCl₃): δ = 8.76 (d, J = 8.4 Hz, 1 H), 8.76 (d, J = 8.4 Hz, 1 H), 8.08 (d, J = 6.8 Hz, 1 H), 7.93 (d, J = 8.1 Hz, 1 H), 7.83 (d, J = 8.1 Hz, 1 H), 7.56–7.50 (m, 1 H), 7.47 (t, J = 7.5 Hz, 1 H), 1.43 (s, 12 H).

The NMR data were in accordance with the literature.[9v]

5,5-Dimethyl-2-(p-tolyl)-1,3,2-dioxaborinane (3p)

Reaction of 1f (19.8 mg, 0.10 mmol) and 5,5,5′,5′-tetramethyl-2,2′-bi(1,3,2-dioxaborinane) (2b; 45.1 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3p (13.1 mg, 5.42·10^–2 mmol, 64%) after purification by column chromatography on silica gel with a mixture of pentane/EtOAc (30:1) as a white solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.70 (d, J = 7.8 Hz, 2 H), 7.18 (d, J = 7.7 Hz, 2 H), 3.76 (s, 4 H), 2.36 (s, 3 H), 1.02 (s, 6 H).

The NMR data were in accordance with the literature.[9k]

4,5,5-Trimethyl-2-(p-tolyl)-1,3,2-dioxaborinane (3q)

Reaction of 1f (19.8 mg, 0.10 mmol) and 5,5,5′,5′,6,6′-hexamethyl-2,2′-bi(1,3,2-dioxaborinane) (2c; 50.8 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave 3q (12.1 mg, 5.55·10^–2 mmol, 56%) after purification by column chromatography on silica gel with a mixture of pentane/EtOAc (30:1) as a colourless oil.

IR (KBr, neat): 2970, 2924, 2330, 2095, 1913, 1610, 1374, 1307, 1165, 815 cm^–1.

¹H NMR (600 MHz, CDCl₃): δ = 7.70 (d, J = 7.7 Hz, 2 H), 7.15 (d, J = 7.7 Hz, 2 H), 4.40–4.25 (m, 1 H), 2.35 (s, 3 H), 1.85 (dd, J = 13.8, 2.9 Hz, 1 H), 1.66–1.52 (m, 1 H), 1.35 (dd, J = 14.2, 6.7 Hz, 9 H).

¹³C NMR (151 MHz, CDCl₃): δ = 140.2, 133.7, 128.2, 70.8, 64.8, 46.0, 31.4, 28.16 (s), 23.2, 21.6 ppm. The carbon directly attached to the boron atom was not detected due to quadrupolar broadening.

¹¹B NMR (128 MHz, CDCl₃): δ = 26.8.

MS (EI): m/z calcd for C₁₃H₁₉BO₂ [M]⁺: 218.1472; found: 218.1470.

2-(4-Chlorophenyl)benzo[d][1,3,2]dioxaborole (3r)

Reaction of 1c (21.9 mg, 0.10 mmol) and bis(catecholato)diboron (2d; 47.6 mg, 0.20 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.05 M) gave the crude product 3r as a brown solid. Several attempts to purify the product were unsuccessful. For this reason, the yield (35%) was determined by ¹H NMR spectroscopy using dimethyl sulfone as an internal standard.

¹H NMR (600 MHz, CDCl₃): δ = 8.01 (d, J = 8.1 Hz, 1 H, product CH_Ar), 7.47 (d, J = 8.2 Hz, 1 H, product CH_Ar), 7.39 (dd, J = 5.8, 3.3 Hz, 1 H, product CH_Ar), 7.33–7.29 (m, 1 H product CH_Ar), 3.00 (s, 6 H internal standard 2 × CH₃).

Product was confirmed by mass spectra.

MS (EI): m/z (%) = 230 (87).

Photoinduced Synthesis of Aryl Thioethers 5; General Procedure

A solution of arylazo sulfone 1 (0.20 mmol) and the respective disulfide 4 (0.40 mmol, 2.00 equiv) in degassed MeCN (2.00 mL, 0.1 M) was poured into a glass vessel, capped, and exposed to blue light (H150 Kessil lamp, 34 W, 420 nm) at r.t. for 12 h. After the completion of the reaction (detected by TLC), the solvent was removed in vacuo, and the crude product was purified by column chromatography on silica gel.

Thioanisole (5a)

Reaction of 1a (36.8 mg, 0.20 mmol) and dimethyl disulfide (4a; 37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5a (12.8 mg, 10.3·10^–2 mmol, 51%) after purification by column chromatography on silica gel with pentane as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.36–7.22 (m, 4 H), 7.14 (tt, J = 5.6, 1.9 Hz, 1 H), 2.49 (s, 3 H).

The NMR data were in accordance with the literature.[20]

4-Chlorothioanisole (5b)

Reaction of 1c (43.7 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5b (21.9 mg, 1.38·10^–1 mmol, 69%) after purification by column chromatography on silica gel with pentane as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.28–7.21 (m, 2 H), 7.21–7.14 (m, 2 H), 2.46 (s, 3 H).

The NMR data were in accordance with the literature.[21]

4-Bromothioanisole (5c)

Reaction of 1d (52.6 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5c (30.3 mg, 14.9·10^–2 mmol, 75%) after purification by column chromatography on silica gel with pentane as a colourless solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.47–7.34 (m, 2 H), 7.20–7.00 (m, 2 H), 2.47 (s, 3 H).

The NMR data were in accordance with the literature.[22]

4-Iodothioanisole (5d)

Reaction of 1e (62.0 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5d (29.0 mg, 11.6·10^–2 mmol, 58%) after purification by column chromatography on silica gel with pentane as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.56–7.51 (m, 2 H), 6.98–6.93 (m, 2 H), 2.43 (s, 3 H).

The NMR data were in accordance with the literature.[22]

4-Methylthioanisole (5e)

Reaction of 1f (39.7 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5e (16.7 mg, 12.1·10^–2 mmol, 60%) after purification by column chromatography on silica gel with pentane as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.24–7.15 (m, 2 H), 7.12 (d, J = 8.1 Hz, 2 H), 2.47 (s, J = 4.6 Hz, 3 H), 2.33 (s, 3 H).

The NMR data were in accordance with the literature.[22]

4-Methoxythioanisole (5f)

Reaction of 1g (42.9 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5f (16.2 mg, 10.5·10^–2 mmol, 53%) after purification by column chromatography on silica gel with pentane as a colourless oil.

¹H NMR (600 MHz, CDCl₃): δ = 7.32–7.21 (m, 2 H), 6.92–6.77 (m, 2 H), 3.79 (s, 3 H), 2.45 (s, 3 H).

The NMR data were in accordance with the literature.[22]

4-(Methylthio)benzonitrile (5g)

Reaction of 1l (41.8 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5g (19.3 mg, 13.1·10^–2 mmol, 66%) after purification by column chromatography on silica gel with a mixture of pentane/Et₂O (50:1) as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.58–7.51 (m, 2 H), 7.32–7.20 (m, 2 H), 2.50 (s, 3 H).

The NMR data were in accordance with the literature.[23]

4-Nitrothioanisole (5h)

Reaction of 1j (45.8 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5h (21.4 mg, 12.6·10^–2 mmol, 63%) after purification by column chromatography on silica gel with a mixture of pentane/Et₂O (90:1) as a yellow solid.

¹H NMR (400 MHz, CDCl₃): δ = 8.24–8.04 (m, 2 H), 7.34–7.14 (m, 2 H), 2.54 (s, 3 H).

The NMR data were in accordance with the literature.[22]

Pentafluoro[4-(methylthio)phenyl]sulfane (5i)

Reaction of 1k (62.1 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5i (29.1 mg, 11.6·10^–2 mmol, 58%) after purification by column chromatography on silica gel with pentane/Et₂O (80:1) as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.70–7.58 (m, 2 H), 7.29–7.20 (m, 2 H), 2.51 (s, 3 H).

¹⁹F NMR (376 MHz, CDCl₃): δ = 87.57–81.95 (m), 63.35 (d, J = 150.2 Hz).

The NMR data were in accordance with the literature.[24]

4-Acetylthioanisole (5j)

Reaction of 1h (45.3 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5j (24.6 mg, 14.8·10^–2 mmol, 74%) after purification by column chromatography on silica gel with pentane as a colourless solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.90–7.83 (m, 2 H), 7.31–7.20 (m, 2 H), 2.56 (s, 3 H), 2.51 (s, 3 H).

The NMR data were in accordance with the literature.[25]

Methyl 2-(Methylthio)benzoate (5k)

Reaction of 1q (48.5 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5k (18.3 mg, 10.0·10^–2 mmol, 50%) after purification by column chromatography on silica gel with a mixture of pentane/Et₂O (90:1) as a colourless solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.99 (dd, J = 7.8, 1.5 Hz, 1 H), 7.50–7.44 (m, 1 H), 7.29–7.27 (m, 1 H), 7.17–7.13 (m, 1 H), 3.93–3.90 (m, 3 H), 2.46 (s, 3 H).

The NMR data were in accordance with the literature.[21]

2-(Methylthio)benzonitrile (5l)

Reaction of 1p (41.8 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5l (14.5 mg, 14.5·10^–2 mmol, 72%) after purification by column chromatography on silica gel with a mixture of pentane/Et₂O (90:1) as a colourless solid.

¹H NMR (600 MHz, CDCl₃): δ = 7.59 (dd, J = 7.7, 1.3 Hz, 1 H), 7.53–7.50 (m, 1 H), 7.32 (d, J = 8.1 Hz, 1 H), 7.23–7.20 (m, 1 H), 2.56 (s, 3 H).

The NMR data were in accordance with the literature.[22]

3-Nitrothioanisole (5m)

Reaction of 1s (33.8 mg, 0.20 mmol) and 4a (37.7 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5m (18.2 mg, 10.8·10^–2 mmol, 54%) after purification by column chromatography on silica gel with a mixture of pentane/Et₂O as a yellow solid.

¹H NMR (600 MHz, CDCl₃): δ = 8.05 (t, J = 1.9 Hz, 1 H), 7.96 (ddd, J = 5.8, 1.9, 0.7 Hz, 1 H), 7.55–7.51 (m, 1 H), 7.43 (t, J = 8.0 Hz, 1 H), 2.56 (s, 3 H).

The NMR data were in accordance with the literature.[21]

Ethyl Phenyl Sulfide (5n)

Reaction of 1a (36.8 mg, 0.20 mmol) and diethyl disulfide (4b; 49 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5n (13.9 mg, 10.1·10^–2 mmol, 50%) after purification by column chromatography on silica gel with pentane as a colourless oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.40–7.25 (m, 4 H), 7.22–7.11 (m, 1 H), 2.95 (q, J = 7.4 Hz, 2 H), 1.32 (dd, J = 9.2, 5.5 Hz, 3 H).

The NMR data were in accordance with the literature.[25]

Diphenyl Sulfide (5o)

Reaction of 1a (36.8 mg, 0.20 mmol) and diphenyl disulfide (4c; 87.3 mg, 0.40 mmol, 2.00 equiv) in MeCN (2.00 mL, 0.1 M) gave 5o (17.2 mg, 9.23·10^–2 mmol, 46%) after purification by column chromatography on silica gel with pentane as a colourless oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.70–6.70 (m, 10 H).

The NMR data were in accordance with the literature.[19]

• References

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• 1b Jana R, Pathak TP, Sigman MS. Chem. Rev. 2011; 111: 1417
• 1c Yamaguchi J, Yamaguchi AD, Itami K. Angew. Chem. Int. Ed. 2012; 51: 8960
• 1d Chauhan P, Mahajan S, Enders D. Chem. Rev. 2014; 114: 8807
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