Coupling of N‐Tosylhydrazones with Terminal Alkynes Catalyzed by Copper(I): Synthesis of Trisubstituted Allenes

The easy way to allenes: An operationally simple reaction under mild conditions has led to the direct formation of trisubstituted allenes (see scheme; Ts=4-toluenesulfonyl). An unprecedented copper–carbene migratory insertion process seems to take place, in contrast to classic copper(I)-catalyzed reactions of diazo compounds.