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

A 1:1 mixture of the π-allyl palladium complex (η 3 -C 3 H 5 )Pd(Cl)PCy 3 ( 1a ) and NaB[3,5-C 6 H 3 (CF 3 ) 2 ] 4 in the presence of HSiEt 3 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.