HETEROCYCLES

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■ Syntheses of Chiral Heterocyclic Compounds via Zirconium-Catalyzed Asymmetric Carboalumination of Alkynes (ZACA Reaction)

Shiqing Xu and Ei-ichi Negishi*

*Herbert C. Brown Laboratories of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, U.S.A.

Abstract

Shortly after the Zr-catalyzed carboalumination of alkynes was discovered in 1978, we sought expansion of the scope of this reaction so as to develop its alkene version for catalytic asymmetric C–C bond formation, namely the ZACA (Zr-catalyzed asymmetric carboalumination of alkenes). However, the discovery of such an asymmetric reaction proved to be quite challenging. The ZACA reaction was finally discovered in 1995 by suppressing three unwanted side reactions, i.e., (i) cyclic carbometalation, (ii) β-H transfer hydrometalation, and (iii) alkene polymerization, represented by the Ziegler-Natta polymerization. Three mutually complementary procedures for the enantioselective synthesis of methyl-substituted 1-alkanols have been developed, which allow highly flexible designs for the syntheses of chiral organic compounds. This review summarizes the syntheses of chiral heterocyclic compounds of biological and medicinal interest via ZACA reaction, which provides a widely applicable, efficient and selective method for catalytic asymmetric C–C bond formation.