Azepine Synthesis from Alkyl Azide and Propargylic Ester via Gold Catalysis

An efficient new method was developed to synthesize multisubstituted 4,5-dihydro-1H-azepine derivatives through the gold-catalyzed reaction of two molecules of propargylic esters with one molecule of alkyl azide. It was proposed that vinyl gold carbenoid, in situ generated from propargylic ester through gold-catalyzed 1,2-rearrangement, was trapped by alkyl azide to give vinyl imine intermediate. These, in turn, could undergo a formal [4 + 3] cycloaddition with another molecule of vinyl gold carbenoid to afford the desired azepine product.