[2 + 1] Cycloaddition of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene. Novel cyclopropane ring formation by a 1,2-shift of a trimethylsilyl group
摘要:
Reaction of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene (1) with vinyl ketones 2a-d in the presence of SnCl4 gave cyclopropane products by a formal [2 + 1] cycloaddition accompanied by 1,2-silicon migration rather than [2 + 2] cycloaddition.
[2 + 1] Cycloaddition of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene. Novel cyclopropane ring formation by a 1,2-shift of a trimethylsilyl group
摘要:
Reaction of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene (1) with vinyl ketones 2a-d in the presence of SnCl4 gave cyclopropane products by a formal [2 + 1] cycloaddition accompanied by 1,2-silicon migration rather than [2 + 2] cycloaddition.
Asymmetric [2 + 1] Cycloaddition Reactions of 1-Seleno-2-silylethene
作者:Shoko Yamazaki、Mayumi Tanaka、Shinichi Yamabe
DOI:10.1021/jo960194u
日期:1996.1.1
The reaction of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene (1) and vinyl ketones 2a-d in the presence of a chiral Lewis acid prepared from TiCl4, Ti((OPr)-Pr-i)(4), (R)- or (S)-1,1'-binaphthol (BINOL), and MS4A gave enantiomerically enriched cis cyclopropane products 3a-d. The enantiomeric excess and chemical yield varied depending on the ratio of TiCl4 and Ti((OPr)-Pr-i)(4) to 1. Reproducible results (43-47% ee/33-41% yields) for cis-1-acetyl-2-[(phenylseleno)(trimethylsilyl)methyl]cyclopropane (3a) were obtained using 1.1 equiv of TiCl4, 0.54-0.65 equiv of Ti((OPr)-Pr-i)(4), and 1.65 equiv of BINOL. The observed enantioselectivity was explained by consideration of the structure of the postulated intermediates, alkoxy titanium-carbonyl complexes, via ab initio MO calculations.
Yamazaki Shoko, Tanaka Mayumi, Yamaguchi Akio, Yamabe Shinichi, J. Amer. Chem. Soc, 116 (1994) N 6, S 2356-2365
A novel one-step [2 + 1] cycloaddition synthesis of cyclopropanes has been developed. Reaction of (E)-1-(phenylseleno)-2-silylethenes 1a,b with vinyl ketones 2a-d and acrolein (2e) in the presence of SnCl4 gave cyclopropane products by a formal [2 + 1] cycloaddition accompanied by 1,2-silicon migration rather than by [2 + 2] cycloaddition. This facile 1,2-silicon shift is rationalized by a remarkable selenium effect. A generated beta-silicon-stabilized zwitterion A is transformed by a 1,2-silicon shift to the more stable selenium-bridged intermediate C. Ab initio MO calculations for model compounds clearly demonstrate that the intermediate C is more stable than A. The selenium-bridged geometry of C shows that preference is for formation of a cyclopropane ring instead of a cyclobutane ring.
[2 + 1] Cycloaddition of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene. Novel cyclopropane ring formation by a 1,2-shift of a trimethylsilyl group
作者:Shoko Yamazaki、Shigeki Katoh、Shinichi Yamabe
DOI:10.1021/jo00027a003
日期:1992.1
Reaction of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene (1) with vinyl ketones 2a-d in the presence of SnCl4 gave cyclopropane products by a formal [2 + 1] cycloaddition accompanied by 1,2-silicon migration rather than [2 + 2] cycloaddition.