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Development, Synthetic Scope, and Mechanistic Studies of the Palladium-Catalyzed Cycloisomerization of Functionalized 1,6-Dienes in the Presence of Silane

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journal contribution
posted on 27.09.2000, 00:00 by Philip Kisanga, Ross A. Widenhoefer
A 1:1 mixture of the π-allyl palladium complex (η3-C3H5)Pd(Cl)PCy3 (1a) and NaB[3,5-C6H3(CF3)2]4 in the presence of HSiEt3 catalyzed the cycloisomerization of diethyl diallylmalonate (2b) to form 4,4-dicarbomethoxy-1,2-dimethylcyclopentane (3b) in 98% yield with 98% isomeric purity. The procedure tolerated a range of functionality including esters, ketones, sulfones, protected alcohols, and substitution at the allylic and terminal olefinic carbon atoms. Cycloisomerization of 2b obeyed zero-order kinetics to >3 half-lives with initial formation of 1,1-dicarboethoxy-4-methyl-3-methylenecyclopentane (4b), followed by secondary isomerization to 3b. Deuterium labeling studies revealed that the conversion of 2b to 4b was accompanied by significant H/D exchange, consistent with an addition/elimination pathway coupled with facile H/D exchange of the Pd−H(D) intermediates with free silane.