| Research Abstract |
Organozirconocene chloride complex, which is known to be a poor nucleophile, showed the enhanced nucleophilicity under transition-metal catalyzed conditions. Thus, alkenylzirconocene chloride complex reacted with α,β-unsaturated carbonyl compounds to give 1,4-addition products in the presence of Rh(I) catalyst. The reaction was extended to α,β-unsaturated compounds, which have a chiral amides auxiliary, and we found that the product was obtained in high diastereoselectivity, thus in optically pure state. Acylzirconocene chloride complex, which has been established as an acyl anion donor by us, showed further usefulness for the formation of carbocyclic compounds. Thus, the Pd-catalyzed reactions of acylzirconocene chlorides with co-alkenyl or-alkynyl α,β-enones afforded bicyclo[3.3.0]compounds, stereoselectively. Interestingly, the reaction of α,w-unsaturated compounds, which possess no α,β-enone functionality, was catalyzed by Ni catalyst to give bicylo[3.1.0] compounds.
The continuing study on the chemistry of low valent zirconocene complex, which can be generated by treating zirconocene dichloride with n-BuLi, indicated that an efficient formation of benzylic zirconocene complex by treating o-alkoxymethl styrene with low valent zirconocene. Formation of carbon-carbon bond from thus generated zirconocene complex was carried out in the presence of Cu catalyst, and thus the important intermediate for the preparation of estrone was efficiently generated by our zirconocene/metal catalyst chemistry.
Elucidations on the nucleophilic reactivity and the synthetic application of organozirconocene complex are our current very active research project, thus we continue the organozirconocene chemistry to find a new and noble carbon-carbon forming reaction.
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