Asymmetric synthesis of isochromanone derivatives <i>via</i> trapping carboxylic oxonium ylides and aldol cascade

Abstract

An efficient asymmetric synthesis of isochromanone derivatives was realized through <i>Z</i>-selective-1,3-OH insertion/aldol cyclization reaction involving acyclic carboxylic oxonium ylides. The combination of achiral dirhodium salts and chiral <i>N</i>,<i>N</i>'-dioxide-metal complexes, along with the use of α-diazoketones instead of α-diazoesters, enables the cascade reaction efficiently. A variety of benzo-fused δ-lactones bearing vicinal quaternary stereocenters were obtained with good to excellent enantioselectivity, bypassing the competitive 1,1-OH insertion and racemic background aldol reaction.