Stereoselective synthesis of 1,3-and 1,4-dicarbonyl-alkenes from cyclopropenes in a catalytic zinc system

Cyclopropenes are well-known vinyl carbene precursors; however, it is still challenging to control the E/Z selectivity of the in situ generation of the C-C double bond. Herein, we designed hydroxyl substituted aromatic enaminones to react with cyclopropenes under zinc promotion to provide & alpha;-allyl-1,3-ketoaldehydes and & alpha;-vinyl-1,4-ketoaldehydes with high regio- and stereo-selectivities. The hydroxyl group is believed to play a key role in controlling the E/Z selectivity of the C-C double bond, which is generated in situ from ring-opening of cyclopropenes. Zinc catalytic platforms are not only compatible with broad substrate scope of enaminones and cyclopropenes, but also beneficial with mild reaction conditions, cheap zinc catalysts and easy-handling procedures. Control experiments and DFT calculations are performed to investigate the possible mechanism, where the hydroxyl group may play a key role in controlling the regio- and stereo-selectivities. This work describes a dual catalytic system for selective synthesis of & alpha;-allyl-1,3-ketoaldehydes and & alpha;-vinyl-1,4-ketoaldehydes through cascade reactions of hydroxyl substituted aromatic enaminones with cyclopropenes under zinc promoted conditions.