Benzopyranoisoxazolidines as Chiral Auxiliaries for Asymmetric Synthesis

摘要

Highly stereoselective α-alkylation of carboxylic acid derivatives (RCH_2COX) can he performed with many known chiral auxiliaries such as oxazolidinone. sultam heterocycles. and others. Here we report new chiral isoxazolidine auxiliaries (la and b).which not only effect equally high asymmetric induction but also offer the following distinct advantages: 1) acyla-tion of the auxiliaries is achieved with an acid chloride and triethylamine. 2) alkylation with β-branched electrophiles can be performedby using their inflates, and 3) alkylated products can be converted directly into the corresponding alcohols, aldehydes, and ketones in one step with recovery of the auxiliary (see Scheme 1).