Observation on the synthesis of allenes by homologation of alk-1-ynes

Abstract

An investigation is reported on the homologation of alk-1-ynes to allenes by the cuprous bromide-catalyzed reaction with formaldehyde and di-isopropylamine, including extension to an aromatic acetylene and a diacetylene. Optimization of yields was studied. A mechanism is proposed involving an intermediate hydrido-cuprate species derived from a 1:1 Mannich base–cuprous bromide π-complex. The mechanism is supported by labelling experiments and observed substituent effects.