Synthesis of Polyfunctional Allenes by Successive Copper‐Mediated Substitutions

Readily available 1,1‐dichloro‐2‐alkynes are versatile starting materials for the synthesis of polyfunctionalized allenes. They can be prepared from commercially available terminal alkynes in a two‐step procedure. The Cu‐mediated reaction of several 1,1‐propargylic derivatives with functionalized alkyl, benzylic, or allylic zinc reagents proceeds exclusively with S N 2′ selectivity and allows a rapid and efficient synthesis of functionalized chloroallenes. These chloroallenes undergo a novel Cu I ‐catalyzed substitution reaction with functionalized arylmagnesium reagents with excellent S N 2 selectivity to give trisubstituted polyfunctionalized allenes. The functional group tolerance is excellent and functionalities, such as cyano, keto, ester, phosphate, trifluoromethyl, and halogens, are well tolerated.