Cyclization/Hydrosilylation of Functionalized Dienes Catalyzed by a Cationic Palladium Phenanthroline Complex
journal contributionposted on 15.10.1999, 00:00 by Ross A. Widenhoefer, Carmine N. Stengone
Mixtures of (phen)PdMe2 (2a) and HBAr‘4 (3a) or (phen)PdMe(Cl) (2b) and NaBAr‘4 (3b) [phen = 1,10-phenanthroline; Ar‘ = 3,5-C6H3(CF3)2] catalyzed the cyclization/hydrosilylation of functionalized 1,6-dienes to form silylated cyclopentanes in good yield and with excellent trans selectivity about the newly formed C−C bond (typically >50:1). A range of tertiary hydrosilanes were employed in the procedure although unhindered trialkylsilanes provided the most consistent results. The protocol tolerated a range of polar functionality including esters, ethers, amides, sulfones, and cyano groups. 4,4-Disubstitution on the diene backbone promoted cyclization, and a homoallylic ester, ketone, or ether directing group was required for efficient cyclization. The procedure tolerated dienes which possessed a single trans-substituted olefin and also tolerated allylic substitution. These substituted dienes underwent cyclization/hydrosilylation to form carbocycles resulting from transfer of the silyl group to the less hindered olefin. Mixtures of 2a and 3a also catalyzed the cyclization/hydrosilylation of functionalized 1,7-dienes to form silylated cyclohexane derivatives. Cyclization/hydrosilylation of 1,7-dienes was typically slower, less stereoselective, and more sensitive to substitution than was cyclization of 1,6-dienes.