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DOI: 10.1055/s-0029-1219183
Thieme Chemistry Journal Awardees - Where Are They Now?Diastereoselective Tandem Iodocarbonate Cyclization of 1,5-Enynes
Publikationsverlauf
Publikationsdatum:
11. Januar 2010 (online)
![](https://www.thieme-connect.de/media/synlett/201003/lookinside/thumbnails/10.1055-s-0029-1219183-1.jpg)
Abstract
A diastereoselective, metal-free tandem iodocarbonatecyclization of 1,5-enyne, emulating the reactivity of gold catalysis is described. The normal selectivity of iodonium reagents for alkene is reversed favoring alkyne activation in the presence of aryl alkynes.
Keywords
enynes - iodocyclization - IBr - tandem reactions - diastereoselectivity
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References and Notes
Key spectral feature of monoalkene carbonation products 3 is as follows: Chemical shift (δ) of CH2I peak is ca. 3.5 ppm (¹H NMR), and 5-15 ppm (¹³C NMR) depending on the diastereomer. Proton and carbon correlation of these resonances is apparent in HSQC spectra of compounds 3.
11The structural and stereochemical identity of the iodocarbonate products 4 were confirmed by the conversion of 4f/4g into 7f/7g (Scheme [²] ), respectively, by the radical deiodination as below. Spectra of 7f/7g matched those of the respective products obtained in Au(I) catalysis.6c For 4o and 4q, relative stereochemistry was based on 1D-NOE spectra.
![](https://www.thieme-connect.de/media/synlett/201003/s110_s2.gif)
Scheme 2
The assignment of iodobromination products 5 was based on the following experiments: i) LRMS (CI) fragmentation data containing 79Br/8¹Br isotope, ii) 1D-NOE spectra of 5g, iii) conversion of 5o into 4o′ (diastereomer of 4o) by Ag(I)-promoted carbonation, iv) conversion of 5o into 6o by E2 elimination (NaOMe), and v) the reaction of 2n with ICl into a mixture of 4n and iodochlorinated product 7n (Scheme [³] ), corresponding to 5n.
![](https://www.thieme-connect.de/media/synlett/201003/s110_s3.gif)
Scheme 3
For a hydride addition on an alkyne: Strozier R. W., Caramella, P.; Houk, K. N. J. Am. Chem. Soc. 1979, 79, 1340; for addition of a weaker nucleophile (olefin in this case) having a later TS, preferential attack of alkyne should be even more pronounced.
16However, in the formation of 4h, 4k, and 4n/5n, diastereomeric products having trans-1,2-vicinal relationship between the two methyl bearing centers were not observed. This observation indicates some degree of concertedness of C-C and C-O bond formations (or less likely, stereoelectronically driven nucleophilic trapping of the cationic center).
17
Typical Procedure
for the IBr-Promoted Tandem Cyclization
To a solution
of 2f (57.3 mg, 0.200 mmol) in CH2Cl2 (1
mL) at -78 ˚C was added dropwise a solution
of IBr (82.7 mg, 0.400 mmol) in CH2Cl2 (1
mL). The mixture was kept stirred at -78 ˚C for
20 min, then aq sat. Na2S2O3 (4
mL) was added at once. The mixture was allowed to warm to r.t. with stirring.
Layers were separated, and the aqueous layer was extracted with
CH2Cl2 (3 × 4 mL). The combined organic layers
were dried (MgSO4), evaporated, and the residue was purified
by silica gel chromatography (EtOAc-hexane = 1:6)
to yield 57.5 mg (81%) of 4f as
a white solid (mp 154-156 ˚C).
Compound 4f: IR (neat): 2916, 1800, 1436, 1350,
1185, 1057 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.45-7.28
(m, 3 H), 7.28-7.15 (m, 2 H), 4.60 (t, J = 3.0
Hz, 1 H), 3.32 (dd, J = 2.2,
16.9 Hz, 1 H), 2.97 (dd, J = 2.6,
17.0 Hz, 1 H), 2.93 (d, J = 15.8
Hz, 1 H), 2.52 (d, J = 15.8
Hz, 1 H), 1.60 (s, 3 H). ¹³C NMR (100
MHz, CDCl3): d = 154.5, 144.5, 144.0, 129.1,
128.6, 128.2, 88.7, 83.6, 82.0, 44.7, 42.7, 26.7. HRMS: m/z calcd for C14H13INaO3 [M + Na]+:
378.9807; found: 378.9809.
Compound 4g:
white solid; mp 114-115 ˚C. IR (neat): 2921, 1790,
1506, 1246, 1052 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.18 (d, J = 8.8 Hz,
2 H), 6.89 (d, J = 8.5
Hz, 2 H), 4.58 (t, J = 2.9
Hz, 1 H), 3.82 (s, 3 H), 3.31 (dd, J = 2.2,
16.9 Hz, 1 H), 2.96 (dd, J = 2.5,
16.9 Hz, 1 H), 2.92 (d, J = 15.8
Hz, 1 H), 2.51 (d, J = 15.8
Hz, 1 H), 1.60 (s, 3 H). ¹³C NMR (100 MHz,
CDCl3): δ = 159.8, 154.5, 144.0, 136.3,
129.6, 114.3, 88.1, 83.7, 82.0, 55.9, 44.8, 42.9, 26.7. Anal Calcd
for C15H15IO4: C, 46.65; H, 3.92.
Found: C, 45.60; H, 4.10. LRMS (CI+): m/z calcd for C15H16IO4 [M+ + H]:
387; found: 387 (100) [M+ + H],
343 (6) [M+ + H - CO2],
325 (67) [M+ + H - CO2 - H2O].
Compound 5g: colorless liquid. IR (neat): 2968,
2926, 1738, 1506, 1279, 1246, 1156, 1085 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.10 (d, J = 8.4 Hz,
2 H), 6.89 (d, J = 8.8
Hz, 2 H), 5.00 (t, J = 4.7
Hz, 1 H), 3.82 (s, 3 H), 3.44 (d br, J = 18.7
Hz, 1 H), 3.07 (d of ABq, J = 7.9
Hz, 1 H), 3.00 (d of ABq, J = 7.9
Hz, 1 H), 2.94 (d br, J = 18.7
Hz, 1 H), 1.81 (s, 3 H), 1.52 (s, 9 H). ¹³C
NMR (100 MHz, CDCl3): δ = 159.6, 153.3,
141.2, 137.9, 129.7, 114.3, 93.1, 83.6, 61.4, 55.9, 47.7, 45.7,
28.8, 28.4. LRMS (CI+): m/z calcd
for C19H25
79BrIO4 [M+ + H]:
523; found: 523 (24) [M+ + H, 79Br],
525 (24) [M+ + H, 8¹Br],
467 (10) [M+ + H - C4H8, 79Br],
469 (8) [M+ + H - C4H8, 8¹Br],
443 (6) [M+ - 79Br],
405 (37) [M+ + H - C4H8 - CO2 - H2O, 79Br],
407 (36) [M+ + H - C4H8 - CO2 - H2O, 8¹Br].
Compound 4n: white solid; mp 105-107 ˚C.
IR (NaCl): 2916, 2850, 1790, 1601, 1511, 1350, 1246, 1057 cm-¹. ¹H NMR
(400 MHz, CDCl3): δ = 7.12 (d, J = 8.8 Hz,
2 H), 6.90 (d, J = 8.4
Hz, 2 H), 4.55 (t, J = 3.7
Hz, 1 H), 3.82 (s, 3 H), 3.24-3.16 (m, 2 H), 2.95 (q, J = 7.3 Hz,
1 H), 1.58 (s, 3 H), 1.07 (d, J = 7.3
Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 159.8,
154.6, 149.6, 136.7, 130.0, 129.8, 114.4, 89.0, 86.0, 81.9, 55.9,
46.3, 43.8, 25.0, 13.4. ES-HRMS: m/z calcd
for C16H17IO4Na [M + Na]+:
423.0069; found: 423.0068.
Compound 5n:
pale yellow liquid. IR (NaCl): 2916, 2930, 1743, 1601, 1506, 1365,
1279, 1242, 1156 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.16 (d, J = 8.4 Hz,
2 H), 6.91 (d, J = 8.8
Hz, 2 H), 5.49 (dd, J = 3.3,
7.7 Hz, 1 H), 4.03 (q, J = 6.9
Hz, 1 H), 3.82 (s, 3 H), 3.37 (dd, J = 7.7,
17.3 Hz, 1 H), 2.77 (dd, J = 3.3,
17.2 Hz, 1 H), 1.70 (d, J = 7.0
Hz, 3 H), 1.51 (s, 9 H), 1.14 (s, 3 H). ¹³C
NMR (100 MHz, CDCl3):
δ = 159.9,
153.6, 152.8, 131.2, 129.5, 114.3, 95.2, 83.1, 78.3, 60.4, 57.4,
55.8, 50.7, 28.4, 21.8, 18.7. LRMS (CI+): m/z calcd for C20H26
79BrIO4 [M+ + H]:
537; found: 537 (22) [M+ + H, 79Br],
539 (22) [M+ + H, 8¹Br],
481 (26) [M+ + H - C4H8, 79Br],
483 (24) [M+ + H - C4H8, 8¹Br],
419 (52) [M+ - BocO, 79Br],
421 (51) [M+ - BocO, 8¹Br],
401 (100) [M+ - Br - C4H8, 79Br].