Carbozirconation and related carbometallation reactions

It has recently been established that carbozirconation with organylzirconocene derivatives evidently requires dipolar (and mostly bimetallic) activation and/or small-ring zirconacycles, especially three-membered ones, that can undergo cyclic carbozirconation (Generalization 6 ) [149]. One of the recent examples has been shown to involve both bimetallic and cyclic organo-zirconium species [150], These reactions can be either stoichiometric or catalytic in Zr. 

Many dozen complex natural products have been synthesized in a highly selective manner by the use of Zr-catalyzed carboalumination of alkynes. Although most of them are not mentioned here due to space limitation, those that have been reported by the author s group over the past few years alone include freelingyne [160], coenzyme Q10 [159], and (3- and y-carotenes [163], which were synthesized with unprecedented efficiency and selectivity. 

It has recently been shown that some of the sluggish reactions, such as those with styrene and w-alkenol derivatives, can be significantly accelerated by the addition of H20, MAO (methylaluminoxane) [167], and IBAO (isobutylaluminoxane) [168], and that the ee values can be improved by several % (Generalization 17). Some of the earlier results discussed above have also been reviewed recently [169,170]. 

4 Stoichiometric bicydization of enynes, diynes, and dienes by cyclic carbozirconation 

5 Stoichiometric intermolecular cyclic carbozirconation of three-membered zirconacycles 

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