Gold(I)‐Catalyzed Diastereoselective Hydroacylation of Terminal Alkynes with Glyoxals

The reaction of an α‐ketoaldehyde and a terminal alkyne in the presence of piperidine and a catalytic amount of AuCl delivers 1,2‐dicarbonyl‐3‐enes, products of the formal hydroacylation of the triple bond. The scope of the method is broad; different aryl substituents on the dicarbonyl unit and on the alkyne are well tolerated. The products can be transformed selectively into vinylquinoxalines. Mechanistic studies, including isotope‐labeling experiments, indicate that after an initial A³‐type conversion to propargylic amines, a subsequent base‐mediated alkyne‐to‐allene isomerization and a hydrolysis of the enamine substructure during the workup deliver the formal hydroacylation products.