The Synthesis of N-TBS-S-Alkynyl
Sulfoximines

Michael Harmata; Chaofeng Huang; Yugang Chen; Pinguan Zheng; Xuefeng Gao; Weijiang Ying

doi:10.1055/s-2008-1077956

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Synlett 2008(13): 2051-2055
DOI: 10.1055/s-2008-1077956

LETTER

The Synthesis of N-TBS-S-Alkynyl Sulfoximines

Michael Harmata*, Chaofeng Huang, Yugang Chen, Pinguan Zheng, Xuefeng Gao, Weijiang Ying
Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, USA
Fax: +1(573)8822754; e-Mail: harmatam@missouri.edu;

Further Information

Publication History

Received 18 April 2008
Publication Date:
15 July 2008 (online)

Abstract
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Abstract

Treatment of β-keto sulfoximines with triflic anhydride and Hünig’s base in toluene resulted in the formation of S-alkynyl sulfoximines in good yield.

Key words

sulfoximine - alkyne - triflic anhydride - Hünig’s base

References and Notes

1a Reggelin M. Zur C. Synthesis 2000, 1

Google Scholar
1b Okamura H. Bolm C. Chem. Lett. 2004, 33: 482

Google Scholar
1c Pyne S. Sulfur Rep. 1999, 21: 281

Google Scholar
1d Johnson CR. Aldrichimica Acta 1985, 18: 3

Google Scholar
2a Lemasson F. Gais H.-J. Raabe G. Tetrahedron Lett. 2007, 48: 8752

Google Scholar
2b Spohr V. Kaiser JP. Reggelin M. Tetrahedron: Asymmetry 2006, 17: 50

Google Scholar
2c Rémy P. Langner M. Bolm C. Org. Lett. 2006, 8: 1209

Google Scholar
2d Harmata M. Ghosh SK. Org. Lett. 2001, 3: 3321

Google Scholar
3 Harmata M. Pavri N. Angew. Chem. Int. Ed. 1999, 38: 2419

Crossref PubMed Google Scholar
4 Back TG. Tetrahedron 2001, 57: 5263

Crossref Google Scholar
5 Craig D. Rosa VG. Synlett 2001, 761

Article in Thieme Connect Google Scholar
6 Leca D. Song K. Amatore M. Festerbank L. Lacote E. Malacria M. Chem. Eur. J. 2004, 10: 906

Crossref PubMed Google Scholar
7 Sklute G. Bolm C. Marek I. Org. Lett. 2007, 9: 1259

Crossref Google Scholar
9 Harmata M. Schlemper EO. Tetrahedron Lett. 1987, 28: 5997

Crossref Google Scholar
10 Bhattacharya SN. Josiah BM. Walton DRM. Organomet. Chem. Synth. 1971, 1: 145

Google Scholar
For examples, see:
11a Harmata M. Tetrahedron Lett. 1988, 29: 5229

Google Scholar
11b Harmata M. Claassen RJ. Barnes CL. J. Org. Chem. 1991, 56: 5059

Google Scholar
11c Harmata M. Herron BF. Tetrahedron 1991, 47: 8855

Google Scholar
11d Harmata M. Kahraman M. Jones DE. Pavri N. Weatherwax SE. Tetrahedron 1998, 54: 9995

Google Scholar
12 Harmata M. Huang C. Adv. Synth. Catal. 2008, 350: 972

Crossref Google Scholar
13 Annunriata R. Cinquini M. Cotzi F. J. Chem. Soc., Perkin Trans. 1 1981, 1109

Crossref Google Scholar
14 Hwang KJ. Logusch EW. Brannigan LH. Thompson MR. J. Org. Chem. 1987, 52: 3435

Crossref Google Scholar
Conditions tried included:
15a
0 ˚C, 1 h, 0.1 M TBAF (2.0 equiv) in THF;

Google Scholar
15b
0 ˚C, 1 h, 0.1 M TBAF-AcOH (1.2 equiv) in THF;

Google Scholar
15c
-78 ˚C → 0 ˚C, 1 h, 0.1 M HF-pyridine (1.2 equiv) in THF;

Google Scholar
15d
23 ˚C, 2 h, 0.05 M n-Bu₄NSiF₂Ph₃ (2.0 equiv) in THF.

Google Scholar
16 Füger B. Sklute G. Marek I. Bolm GY. Bolm C. Synlett 2008, 116

Article in Thieme Connect Google Scholar
17 Kolb HC. Finn MG. Sharpless KB. Angew. Chem. Int. Ed. 2001, 40: 2004

Crossref PubMed Google Scholar

8

This is based on a substructure search in Scifinder Scholar.

18

General Experimental Procedures: To a solution of DIPEA (2.5 mmol) in THF (10 mL) at 0 ˚C, was added BuLi (2.5 mmol) with stirring. After 10 min, the solution was cooled to -78 ˚C, and slowly added to a flask that contained 9 (2 mmol) in THF (10 mL) at -78 ˚C. The solution was warmed to r.t. for 15 min, then was cooled back to -78 ˚C. Ester was added (10 mmol) and the solution was warmed to r.t. and then refluxed for 8 h. After TLC showed no starting material, the solution was quenched by sat. NH₄Cl (10 mL), and extracted with Et₂O (3 × 10 mL). The combined organic phases were washed with brine (10 mL), and dried with Na₂SO₄. Removal of solvent and chromatographic purification afforded keto sulfoximines 10.
Procedure A: To 10 (1 mmol) in toluene (5 mL) at r.t. was slowly added DIPEA (6.0 equiv), followed by triflate anhydride (2.3 equiv). The solution was refluxed until TLC showed no starting material remained. It was quenched by sat. NH₄Cl solution (10 mL), and the aqueous layer was extracted with Et₂O (3 × 10 mL). The combined organic layers were washed with brine (10 mL) and dried with Na₂SO₄. Removal of solvent and chromatographic purification afforded S-alkynyl sulfoximines 11.
Procedure B: To a solution of β-keto sulfoximine (1 mmol) in toluene (10 mL) at -40 ˚C was added dropwise DIPEA (6.0 equiv) followed by Tf₂O (2.3 equiv). The solution was stirred for 5 h. The reaction was quenched with sat. NH₄Cl (5 mL), extracted with EtOAc (3 × 10 mL), washed with brine (10 mL), dried with Na₂SO₄ and concentrated in vacuo to give an enol triflate. The triflate was purified by chromatography, eluting with 20% EtOAc in hexane. Due to instability of enol triflate, elimination was carried out immediately. Into a solution of enol triflate (0.5 mmol) in toluene (6 mL) was added DIPEA (3.0 equiv) at r.t. and the solution was stirred at 70 ˚C for 4 h. The reaction was quenched with sat. NH₄Cl solution (5 mL), extracted with EtOAc (3 × 10 mL), washed with brine, dried with Na₂SO₄ and concentrated in vacuo to give a colorless oil. The oil was purified by chromatography, eluting with 20% EtOAc in hexane, to give the pure final product.

19

Data on selected compounds: 10a: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.85-7.92 (m, 4 H), 7.38-7.54 (m, 6 H), 4.70 (d, J = 12.6 Hz, 1 H), 4.54 (d, J = 12.6 Hz, 1 H), 0.83 (s, 9 H),
-0.01 (d, J = 10.5 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 189.1, 143.5, 136.5, 133.6, 132.6, 129.5, 128.7, 128.5, 127.9, 67.8, 25.8, 20.7, 17.9, -2.6, -2.6. IR (CH₂Cl₂): 3064, 2949, 2921, 2855, 1679, 1446, 1274, 1160, 829 cm^-¹. HRMS: m/z calcd for C₂₀H₂₇NO₂SSiNa⁺: 396.1429; found: 396.1315. 10b: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.80-7.82 (m, 2 H), 7.26-7.50 (m, 7 H), 4.80 (d, J = 13.0 Hz, 1 H), 4.72 (d, J = 13.0 Hz, 1 H), 0.86 (s, 9 H), 0.01-0.30 (s, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 191.0, 143.0, 137.8, 132.5, 132.4, 131.4, 130.8, 130.4, 128.6, 127.8, 126.8, 70.8, 17.9, -2.6, -2.7. IR (CH₂Cl₂): 3065, 2922, 2849, 1686, 1286, 1139, 829 cm^-¹. HRMS: m/z calcd for C₂₀H₂₆ClNO₂SSiNa⁺: 430.1034; found: 430.1021. 10c: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.85-7.87 (m, 2 H), 7.48-7.57 (m, 3 H), 4.05 (d, J = 12.5 Hz, 1 H), 4.03 (d, J = 12.5 Hz, 1 H), 2.33 (s, 3 H), 0.90 (s, 9 H), 0.05 (d, J = 11.5 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 191.2, 143.2, 132.7, 128.8, 127.6, 72.4, 31.4, 25.8, 17.9, -2.6, -2.7. IR (CH₂Cl₂): 3068, 2949, 2929, 2851, 1707, 1290, 1143, 820 cm^-¹. HRMS: m/z calcd for C₁₅H₂₅NO₂SSiNa⁺: 334.1267; found: 334.1262. 10d: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.83-7.85 (m, 2 H), 7.47-7.55 (m, 3 H), 4.14 (d, J = 12.5 Hz, 1 H), 4.00 (d, J = 12.5 Hz, 1 H), 2.72-2.78 (m, 1 H), 1.60-1.75 (m, 5 H), 1.22-1.26 (m, 5 H), 0.90 (s, 9 H), 0.03 (d, J = 12.5 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 202.2, 143.3, 132.6, 128.7, 127.7, 69.3, 51.0, 28.1, 27.8, 25.8, 25.6, 25.5, 25.2, 17.9, -2.6, -2.6. IR (CH₂Cl₂): 3068, 2921, 2851, 1707, 1446, 1298, 1147, 824 cm^-¹. HRMS: m/z calcd for C₂₀H₃₃NO₂SSiNa⁺: 402.1893; found: 402.1885. 10e: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.86-7.87 (m, 2 H), 7.50-7.58 (m, 3 H), 4.16 (d, J = 12.5 Hz, 1 H), 4.06 (d, J = 12.5 Hz, 1 H), 3.00 (q, J = 7.0 Hz, 1 H), 1.06 (d, J = 7.0 Hz, 6 H), 0.91 (s, 9 H), 0.06 (d, J = 11.5 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 203.0, 143.2, 132.6, 128.8, 127.8, 69.3, 25.8, 17.9, 17.7, 17.5, -2.6, -2.7. IR (CH₂Cl₂): 3065, 2963, 2849, 1719, 1294, 1155, 829
cm^-¹. HRMS: m/z calcd for C₁₇H₂₉NO₂SSiNa⁺: 362.1580; found: 362.1572. 10f: oil. ^¹H NMR (250 MHz, CDCl₃): δ = 7.84-7.88 (m, 2 H), 7.51-7.59 (m, 3 H), 5.74 (ddt, J = 4.0, 7.0, 14.0 Hz, 1 H), 5.10 (m, 2 H), 4.04 (d, J = 12.5 Hz, 1 H), 4.04 (d, J = 12.5 Hz, 1 H), 2.50-2.58 (m, 2 H), 2.03 (q, finely split, J = 7.0 Hz, 2 H), 1.65 (m, 2 H), 0.91 (s, 9 H), 0.04 (d, J = 3.0 Hz, 6 H). ^¹³C NMR (62.9 MHz, CDCl₃): δ = 199.2, 143.2, 137.7, 132.7, 128.8, 127.7, 115.3, 71.5, 43.6, 32.7, 25.8, 22.3, 17.9, -2.6, -2.7. IR (CH₂Cl₂): 3068, 2949, 2929, 2851, 1707, 1290, 1143, 820 cm^-¹. HRMS: m/z calcd for C₁₉H₃₁NO₂SSiNa⁺: 388.1737; found: 388.1729. 10g: oil. ^¹H NMR (250 MHz, CDCl₃): δ = 7.85-7.88 (m, 2 H), 7.48-7.62 (m, 3 H), 4.05 (d, J = 12.5 Hz, 1 H), 4.05 (d, J = 12.5 Hz, 1 H), 2.60-2.84 (m, 2 H), 1.03 (t, J = 7.2 Hz, 3 H), 0.92 (s, 9 H), 0.07 (s, 3 H), 0.04 (s, 3 H). ^¹³C NMR (62.5 MHz, CDCl₃): δ = 199.7, 143.2, 132.6, 128.8, 127.7, 71.3, 37.7, 25.8, 17.9, 7.3, -2.58, -2.64. IR (CH₂Cl₂): 2953.9, 2921.2, 2847.6, 1715.7, 1298.9, 1147.7, 833.1, 767.7 cm^-¹. HRMS: m/z calcd for C₁₆H₂₇NO₂SSiNa⁺: 348.1423; found: 348.1415. 10h: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.89-7.91 (m, 2 H), 7.49-7.58 (m, 6 H), 7.40-7.41 (m, 3 H), 6.94 (d, J = 16.0 Hz, 1 H), 4.31 (d, J = 12.5 Hz, 1 H), 4.28 (d, J = 12.5 Hz, 1 H), 0.90 (s, 9 H), 0.08 (s, 3 H), 0.05 (s, 3 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 188.1, 144.8, 143.2, 134.0, 132.7, 130.9, 128.8, 128.7, 128.6, 127.8, 125.3, 71.1, 25.8, 17.9, -2.51, -2.58. IR (CH₂Cl₂): 2953.9, 2925.3, 2855.8, 1605.4, 1323.5, 1294.8, 1147.7, 824.9 cm^-¹. HRMS: m/z calcd for C₂₂H₂₉NO₂SSiNa⁺: 420.1580; found: 420.1578. 10i: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.84-7.85 (m, 2 H), 7.48-7.56 (m, 3 H), 4.00 (d, J = 12.5 Hz, 1 H), 4.00 (d,
J = 12.5 Hz, 1 H), 2.56 (dd, J = 7.0, 12.0 Hz, 2 H), 1.61-1.80 (m, 7 H), 0.88-1.28 (m, 13 H), 0.04 (d, J = 10.0 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 198.8, 143.1, 132.6, 128.7, 127.7, 71.6, 51.8, 33.1, 32.9, 26.1, 25.9, 25.8, 17.9, -2.6,
-2.6. IR (CH₂Cl₂): 3064, 2921, 2855, 1711, 1298, 1143, 824 cm^-¹. HRMS: m/z calcd for C₂₁H₃₅NO₂SSiNa⁺: 416.2050; found: 416.2044. 10j: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.86 (d, J = 7.5 Hz, 2 H), 7.54 (d, J = 1.5 Hz, 1 H), 7.53 (t,
J = 7.5 Hz, 1 H), 7.47 (t, J = 7.5 Hz, 2 H), 7.22 (d, J = 3.5 Hz, 1 H), 6.52 (dd, J = 1.5, 3.5 Hz, 1 H), 4.54 (d, J = 12.5 Hz, 1 H), 4.38 (d, J = 12.5 Hz, 1 H), 0.84 (s, 9 H), 0.03 (s, 3 H), 0.01 (s, 3 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 177.4, 152.8, 147.6, 143.6, 132.9, 129.0, 128.2, 119.8, 113.0, 68.2, 26.0, 18.1, -2.4. IR (CH₂Cl₂): 2953, 2929, 2851, 1621, 1429, 1204, 1004 cm^-¹. HRMS: m/z calcd for C₁₈H₂₅NO₃SSiNa⁺: 386.1217; found: 386.1220. 10k: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 7.97 (s, 4 H), 7.85 (d, J = 7.5 Hz, 4 H), 7.56 (t, J = 7.5 Hz, 2 H), 7.49 (t, J = 7.5 Hz, 4 H), 4.69 (d, J = 12.5 Hz, 1 H), 4.68 (d, J = 12.5 Hz, 1 H), 4.58 (d, J = 12.5 Hz, 1 H), 4.57 (d, J = 12.5 Hz, 1 H), 0.83 (s, 9 H), 0.81 (s, 9 H), 0.00 (s, 6 H), -0.02 (s, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 188.9, 143.6, 140.0, 133.1, 129.7, 129.1, 128.2, 68.5, 26.0, 18.2, -2.35, -2.39. IR (CH₂Cl₂): 2949, 2917, 2851, 1679, 1315, 1151, 1000 cm^-¹. HRMS: m/z calcd for C₂₄H₄₈N₂O₄S₂Si₂Na⁺: 691.2486; found: 691.2492. 11a: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.12-8.13 (m, 2 H), 7.32-7.58 (m, 8 H), 1.05 (s, 9 H), 0.30 (d, J = 3.0 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 145.5, 132.6, 132.2, 130.6, 128.8, 128.5, 127.0, 119.2, 89.8, 89.2, 31.5, 25.9, 18.2, -2.9, -3.4. IR (CH₂Cl₂): 3060, 2953, 2921, 2851, 2169, 1315, 1155, 1082, 833, 673 cm^-¹. 11b: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.10-8.12 (m, 2 H), 7.22-7.58 (m, 7 H), 1.00 (s, 9 H), 0.28 (s, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 145.5, 137.0, 133.8, 132.7, 131.4, 129.5, 128.8, 127.0, 126.6, 119.6, 94.0, 85.6, 25.9, 18.1, -2.9, -3.4. IR (CH₂Cl₂): 3064, 2953, 2929, 2851, 2177, 1470, 1327, 1160, 816 cm^-¹. HRMS: m/z calcd for C₂₀H₂₄ClNOSSiNa⁺: 412.0929; found: 412.0929. 11c: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.00-8.02 (m, 2 H), 7.48-7.55 (m, 3 H), 1.94 (s, 3 H), 0.97 (s, 9 H), 0.20 (s, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 145.7, 132.4, 128.7, 126.8, 88.8, 81.6, 25.8, 18.1, 3.9, -3.0, -3.5. IR (CH₂Cl₂): 3064, 2949, 2925, 2855, 2202, 1327, 1160, 824 cm^-¹. HRMS: m/z calcd for C₁₅H₂₃NOSSiNa⁺: 316.1162; found: 316.1155. 11d: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.00-8.04 (m, 2 H), 7.49-7.53 (m, 3 H), 2.42-2.52 (m, 1 H), 1.74-1.82 (m, 4 H), 1.35-1.55 (m, 2 H), 1.20-1.34 (4 H), 0.98 (s, 9 H), 0.22 (d, J = 7.5 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 146.1, 132.2, 128.7, 126.7, 96.0, 82.3, 31.1, 28.9, 25.9, 25.4, 24.6, 18.2, -2.9, -3.4. IR (CH₂Cl₂): 3072, 2933, 2855, 2185, 1446, 1323, 1168, 829 cm^-¹. HRMS: m/z calcd for C₂₀H₃₁NOSSiNa⁺: 384.1788; found: 384.1759. 11e: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.00-8.02 (m, 2 H), 7.48-7.55 (m, 3 H), 2.64 (q, J = 7.0 Hz, 1 H), 1.16 (d, J = 7.0 Hz, 6 H), 0.98 (s, 9 H), 0.22 (d, J = 8.0 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 145.8, 132.3, 128.7, 126.8, 97.0, 81.5, 25.8, 21.4, 21.3, 20.6, 18.1, -3.0,
-3.5. IR (CH₂Cl₂): 3064, 2949, 2925, 2855, 2202, 1327, 1160, 824 cm^-¹. HRMS: m/z calcd for C₁₅H₂₇NOSSiNa⁺: 344.1475; found: 344.1470. 11f: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.00-8.04 (m, 2 H), 7.49-7.55 (m, 3 H), 5.63-5.76 (m, 1 H), 4.94-5.01 (m, 2 H), 2.30 (t, J = 7.2 Hz, 2 H), 2.08 (q, finely split, J = 7.2 Hz, 2 H), 1.60 (p, J = 7.2 Hz, 2 H), 0.98 (s, 9 H), 0.22 (d, J = 5.5 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 146.0, 136.8, 132.4, 128.7, 126.8, 115.8, 92.3, 82.6, 32.6, 26.4, 25.9, 18.1, 18.1, -2.9, -3.4. IR (CH₂Cl₂): δ = 3068, 2949, 2852, 2193, 1442, 1335, 1164
cm^-¹. 11g: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.01-8.03 (m, 2 H), 7.51-7.56 (m, 3 H), 2.31 (q, J = 7.5 Hz, 2 H), 1.15 (t, J = 7.5 Hz, 3 H), 0.98 (s, 9 H), 0.23 (s, 3 H), 0.22 (s, 3 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 145.7, 132.3, 128.6, 126.8, 93.6, 81.6, 25.8, 18.1, 12.5, 12.0, -3.01, -3.53. IR: 2953.9, 2925.3, 2847.6, 2193.8, 1474.6, 1450.1, 1331.6, 1168.2, 829.0, 775.9 cm^-¹. HRMS: m/z calcd for C₁₆H₂₅NOSSiNa⁺: 330.1318; found: 330.1316. 11i: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.01-8.02 (m, 2 H), 7.47-7.53 (m, 3 H), 2.17 (d, J = 6.5 Hz, 2 H), 1.66-1.72 (m, 5 H), 1.45-1.55 (m, 1 H), 1.05-1.20 (m, 3 H), 0.98 (s, 9 H), 0.92-0.94 (m, 2 H), 0.21 (d, J = 6.5 Hz, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 146.1, 132.3, 128.6, 126.7, 92.1, 83.1, 36.5, 32.5, 26.4, 25.8, 25.8, 18.1, -2.9, -3.4. IR (CH₂Cl₂): 3064, 2925, 2847, 2189, 1315, 1168, 824 cm^-¹. HRMS: m/z calcd for C₂₁H₃₃NOSSiNa⁺: 398.1940; found: 398.1944. 11j: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.06 (d, J = 7.5 Hz, 2 H), 7.59 (t, J = 7.5 Hz, 1 H), 7.53 (t, J = 7.5 Hz, 2 H), 7.46 (dd, J = 0.5, 1.5 Hz, 1 H), 6.80 (dd, J = 0.5, 1.5 Hz, 1 H), 6.42 (dd, J = 1.5, 3.5 Hz, 1 H), 1.00 (s, 9 H), 0.27 (s, 3 H), 0.25 (s, 3 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 146.3, 145.4, 134.4, 133.0, 129.2, 127.5, 120.3, 111.7, 94.4, 79.7, 26.1, 18.4,
-2.8, -3.4. IR (CH₂Cl₂): 2949, 2925, 2851, 2161, 1470, 1323, 1168 cm^-¹. HRMS: m/z calcd for C₁₈H₂₃NO₂SSiNa⁺: 368.1111; found: 368.1112. 11k: oil. ^¹H NMR (500 MHz, CDCl₃): δ = 8.06 (d, J = 7.5 Hz, 4 H), 7.58 (t, J = 7.5 Hz, 2 H), 7.54 (t, J = 7.5 Hz, 4 H), 7.41 (s, 4 H), 1.00 (s, 18 H), 0.25 (s, 6 H), 0.24 (s, 6 H). ^¹³C NMR (125.8 MHz, CDCl₃): δ = 145.3, 133.1, 132.4, 129.2, 127.4, 121.6, 92.5, 87.7, 26.1, 18.4, -2.7, -3.2. IR (CH₂Cl₂): 2949, 2925, 2855, 2169, 1331, 1164, 829 cm^-¹. HRMS: m/z calcd for C₃₄H₄₄N₂O₂S₂Si₂Na: 655.2275; found: 655.2279.