Highly Regioselective Cascade Formal Nucleophilic Substitution and Aldol Condensation of 2-Aroyl-1-chlorocyclopropanecarboxylic Esters

A highly regioselective cascade formal nucleophilic substitution and aldol reaction of 2-aroyl-1-chlorocyclopropanecarboxylic esters with salicylic aldehydes is described. Under basic conditions, 2-aroyl-1-chlorocyclopropanecarboxylic esters are easily converted into cyclopropene intermediates by simple 1,2-elimination of hydrogen chloride. This highly reactive cyclopropene quickly combines with salicylic aldehyde through a regioselective oxa-addition to the strained C=C bond and a subsequent intramolecular aldol reaction to construct C-O and C-C bonds concomitantly and afford tetrahydrocyclopropa[b]chromene derivatives.