Indium(I) bromide-promoted stereoselective preparation of cyclopropanes via sequential aldol-type coupling/elimination/Michael-induced ring closure reaction from α,α-dichloroacetophenone and aldehydes

The indium enolate generated from indium(I) bromide and α,α-dichloroacetophenone reacts with aldehydes to produce (syn + anti)-2-chloro-3-hydroxy-propan-1-ones which can be converted to their trans-prop-2-en-1-ones derivatives upon reaction with an extra equivalent of InBr. The enones undergo Michael-induced ring closure reactions with an extra equivalent of the initial enolate to afford the corresponding cyclopropane derivatives, according to a sequenced reaction mechanism.