Diastereoselective, Enantioselective, and Regioselective Carboalumination Reactions Catalyzed by Zirconocene Derivatives

Abstract

Coordinatively unsaturated alkylzirconocene derivatives can undergo stereo-, and regioselective carbometallation reactions of synthetic utility via either bimetallic activation or formation of active three-membered zirconacycles. The Zr-catalyzed carboalumination of alkynes is an example of the former. The Zr-catalyzed methylalumination, in particular, has been developed into a generally applicable reaction of high synthetic utility, and it has been applied to the synthesis of about 100 complex natural products. Highly promising is the Zr-catalyzed asymmetric carboalumination of alkenes featuring novelty and high efficiency. With further improvements, it promises to become another synthetically useful reaction of widespread use. Use of isoalkylalanes in the above-mentioned reactions leads to potentially attractive and useful hydrogen-transfer hydrometallation reactions. Unlike Al, other metals including Li, Mg, and Zn have tended to participate in the reactions proceeding via zirconacycles. Some of these reactions also provide highly efficient routes to compounds that are otherwise difficult to access. Structural and mechanistic aspects of these carbometallation reactions are discussed in some detail.