Recent Advances in Copper-Catalyzed Tandem Reactions of Alkynes, Allenes, and Allenynes

Alkynes and allenes are basic building blocks in organic synthesis owing to their commercial availability, relative stability, and uncomplicated preparation. Regioselective transformation of alkynes and allenes is a critical process for the synthesis of value-added compounds. Accurate regulation of these transformations enables the practical and divergent synthesis of complex molecules with new functionalities. This review outlines the recent progress toward the development of copper-catalyzed cyclization reactions of alkynes, allenes, and allenynes. Copper-catalyzed oxidation reactions of alkynes with N-oxides via α-oxo copper carbenes for the efficient construction of various functionalized organic molecules are developed. Importantly, the copper-catalyzed asymmetric alkyne oxidation with N-oxides, which represents the first non-noble metal-catalyzed alkyne oxidation, is reported by the in situ generated α-oxo copper carbenes. Then, an efficient copper-catalyzed desymmetric cyclization reaction of allenes via a presumable copper carbene intermediate and a highly selective 1,2-N shift process is disclosed. In particular, this protocol represents the first example of non-noble-metalcatalyzed allene cyclization via the donor/donor copper carbene intermediates. Based on these compelling findings, the precise transformation of alkynes, allenes, and allenynes by copper catalysts will accelerate novel insights into the exploration of alkyne and allene chemistry.