Asymmetric [4+2] Annulation of C1 Ammonium Enolates with Copper-Allenylidenes

Abstract

An asymmetric catalytic decarboxylative [4+2] annulation of 4-ethynyl dihydrobenzooxazinones and carboxylic acids has been established by cooperative copper and nucleophilic Lewis base catalysis. A C1 ammonium enolate and copper-allenylidene complex, each catalytically generated from different substrates, underwent a cascade asymmetric propargylation and lactamization process to yield optically active 3,4-dihydroquinolin-2-one derivatives with excellent levels of stereoselectivity (up to 99 % ee, 95:5 d.r.).

Keywords: C1 ammonium enolates; [4+2] annulations; cooperative catalysis; copper; heterocycles.