Synthesis of Homopropargylamines from 2-Cyanoazetidines

2-Cyanoazetidines, easily accessible from β-amino alcohols, undergo ring-cleavage upon reaction with trimethylsilylazide and catalytic amounts of Bu2SnO, to give the corresponding homopropargylamines which are isolated as their N-Boc protected derivatives. The scope of this reaction, which constitutes a new way to access these highly relevant building blocks, is examined in detail. The proposed mechanism involves a tin-catalyzed cycloaddition of the nitrile moiety with the azide to give the corresponding tetrazole, which decomposes with the extrusion of two molecules of dinitrogen to produce an intermediate vinylidene carbene that finally evolves to give the alkyne.