Enantioselective Cyclopropanation Reactions with Planar‐Chiral Pyridinium Ylides: A Substituent Effect and a Remote Steric Effect

Abstract

AbstractNovel planar‐chiral pyridinium ylides were designed, and generated in situ from the corresponding pyridinium salts with triethylamine. Ylides with a common parapyridinophane skeleton reacted efficiently with electron‐deficient dicyanoalkenes, or malononitriles, to produce optically active cyclopropane derivatives with high enantioselectivity (up to 99% ee). Remote steric effects were observed on the enantioselectivities, where the R2 groups of the pyridinophane core resulted in higher ee values of the products. Density function theory (DFT) calculations are in good agreement with our experimental results: the energetically favored transition state leads to the major stereoisomer, namely the trans‐cyclopropane products.