Asymmetric [2 + 1] Cycloaddition Reactions of 1-Seleno-2-silylethene
journal contributionposted on 14.06.1996, 00:00 by Shoko Yamazaki, Mayumi Tanaka, Shinichi Yamabe
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(OiPr)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(OiPr)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(OiPr)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.