Tandem Reaction of Allenoate Formation and Cyclization: Divergent Synthesis of Four- to Six-Membered Heterocycles.

Tandem reactions of copper-catalyzed cross-coupling of N-substituted prop-2-yn-1-amines with diazoacetates and subsequent cyclization have been developed to prepare several types of four- to six-membered heterocycles. Copper-catalyzed allenoate formation has been proven as the key step for the diverse annulations. Importantly, on the basis of the choice of different N-protecting groups of the alkyne substrates, methods toward 5,6-dihydropiperidin-2-ones, 2-methyleneazetidines, and furan derivatives have been well established.