Organocatalytic formal [2+2] cycloaddition initiated by vinylogous Friedel-Crafts alkylation: enantioselective synthesis of substituted cyclobutane derivatives.

An organocatalytic vinylogous Friedel-Crafts alkylation-initiated formal [2+2] cycloaddition was successfully developed based on tandem iminium-enamine activation of enals. Transformable pyrrole-functionalized cyclobutanes with three contiguous stereocenters were readily obtained with excellent levels of regio-, diastereo- and enantiocontrol.