General palladium-catalyzed aerobic dehydrogenation to generate double bonds

Abstract

We describe a general dehydrogenation procedure to form α,β-unsaturated aldehydes, ketones, esters and azobenzenes under very mild conditions, requiring catalytic commercial Pd(OAc)₂, a catalytic weak inorganic base and air as the sole oxidant. In the presence of a diazafluorenone ligand, this process converts aliphatic aldehydes to α,β-unsaturated aldehydes in an open-flask fashion at ambient pressure and temperature. A broad spectrum of substrates, including aldehydes, ketones, esters, alcohols and hydrazines, were conveniently dehydrogenated under a relatively uniformed protocol. A mechanism involving β-elimination-driven enolization equilibrium shift was proposed.