Cyclization/Hydrosilylation of Functionalized Dienes Catalyzed by a Cationic Palladium Phenanthroline Complex

Abstract

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.

Cyclization/Hydrogermylation of Functionalized 1,6-Dienes Catalyzed by Cationic Palladium Complexes

“…Our initial attempt to effect cyclization/hydrogermylation of dimethyl diallylmalonate ( 1 ) employed a procedure analogous to our optimized procedure for palladium-catalyzed cyclization/hydrosilylation . For example, reaction of 1 and HGeEt 3 (1.2 equiv) in the presence of a 1:1 mixture of (phen)Pd(Me)Cl and NaBAr 4 (5 mol %) (phen = 1,10-phenanthroline; Ar = 3,5-C 6 H 3 (CF 3 ) 2 ) in 1,2-dichloroethane (DCE) at room temperature for 1 h formed a 9:1 mixture of trans -1,1-dicarbomethoxy-3-[(triethylgermyl)methyl]-4-methylcyclopentane ( 2 ) and 1,1-dicarbomethoxy-3,4-dimethylcyclopentane ( 3 ) along with traces of isomers of 1 (∼5%), as determined by GC/MS analysis of the crude reaction mixture (Table , entry 1) .…”

“…We recently reported several related protocols for the cyclization/hydrosilylation of 1,6- , and 1,7-dienes , and for the asymmetric cyclization/hydrosilylation of 1,6-dienes catalyzed by cationic palladium complexes (Scheme ). These procedures were characterized by high activity, good stereoselectivity and functional group compatibility, and low air and moisture sensitivity.…”

Silylated Cyclohexadienes in Radical Chain Hydrosilylations

“…The cyclization product 38, e.g., was oxidized to the alcohol 43 in 73% yield [25]. Formally, the above hydrosilylation process can, thus, be regarded as a radical anti-Markovnikov hydration.…”

Hydroelementation of diynes

“…The catalyst was found to be inactive in the cyclisation/hydrosilylation of separated dienes (for which palladium analogs were active), making this process highly selective. [222][223][224][225] The reactions were carried out for 10 min-3 h at 110 1C in toluene for different silanes 207a, 395-398 (Scheme 80). 158 The same group developed a diimine cationic Pt complex, [PhNQC(Me)C(Me)QNPh]PtMe 2 400, which was much more active and selective than the complex with phenanthroline 399.…”