Cross Carbonyl‐Olefin Metathesis of Unactivated Olefins

A method for the olefination of aryl aldehydes with unactivated alkenes via cross carbonyl‐olefin metathesis is described. Reaction of an aldehyde substrate with a cis −1,2‐disubstituted or monosubstituted olefin using the HBF ₄ salt of 2,3‐diazabicyclo[2.2.2]octane results in high‐yielding olefination with exclusive trans stereoselectivity. The reaction is shown to accommodate diverse substitution on the aldehyde, including protic functionality that would complicate traditional olefination methods. We show that product inhibition arising from the aliphatic aldehyde side product limits catalytic turnover, but that distillative removal of this component renders catalysis feasible.