Enantioselective diene cyclization/hydrosilylation catalyzed by optically active palladium bisoxazoline and pyridine-oxazoline complexes

A 1:1 mixture of (N-N)Pd(Me)Cl [N-N=(S,S)-4,4'-dibenzyl-4,5,4',5'-tetrahydro-2,2'-bisoxazoline] (S,S-4a) and NaBAr4 [Ar=3,5-C6H3/CF3)(2)] (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of dimethyl diallylmalonate (2) and triethylsilane at -30 degrees C for 48 h to form an 8.1:1 mixture of the silylated carbocycle (S,S)-trans-1,1-dicarbomethoxy-4-methyl-3-[(triethylsilyl)methyl]cyclopentane (S,S-3) (95% de, 72% eel and dimethyl 3,4-dimethylcyclopentane-1,1-dicarboxylate (S,S-6) in 64% combined yield. In comparison, a 1:1 mixture of the palladium pyridine-oxazoline complex (N-N)Pd(Me)Cl [N-N=(R)-(+)-4-isopropyl-2-(2-pyridinyl)-2-oxazoline] (R-5b) and NaBAr4 (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of 2 and triethylsilane at -32 degrees C for 24 h to form carbocycle S,S-3 in 82% yield (> 95% de, 87% eel as the exclusive product. Asymmetric diene cyclization catalyzed by complex R-5b was compatible with a range of functional groups and produced carbocycles with up to 91% ee. The procedure also tolerated substitution at a terminal olefinic position and at the allylic position of the diene.