Three-Component GaHal3-Promoted Reactions of Substituted Methylidenemalonates and Donor-Acceptor Cyclopropanes with Propargyl Halides: Cascade Diastereoselective Construction of Five-Membered Lactones.

A new cascade three-component process for high trans,trans-diastereoselective assembly of five-membered (1-halovinyl)lactones has been developed. The process is based on reactions of substituted methylidenemalonates and cyclopropanedicarboxylates with 3-haloprop-1-ynes in the presence of GaHal3 and involves the intermediate in situ generation of 1,2-zwitterionic gallium complexes with [Ga(L)3]3+[GaX4-]3 composition. Chloro, bromo, and iodo derivatives can be obtained successfully. Mechanistic and stereochemical aspects of the process we developed have been studied and considered in detail.