Biaryl and atropisomeric biaryl aldehyde synthesis by one-step, metal-free benzannulation of aryl enals and propiolates

A new method involving the benzannulation of aromatic enals and two alkyl propiolate molecules has been developed as powerful route to biaryl aldehydes simply via the promotion of dimethyl amine. The benzannulation process in the absence of oxidant addtive tolerates successfully the formyl group in the enal component, leading to the straightforeward one-step synthesis of biaryl and atropisomeric aldehydes. A enamine activation based on the aza-Michael addition of dimethyl amine to the propiolate as well as the amine elimination-based generation of cyclodiene intermediate constitute the major factors enabling the titled reactions.