Palladium-catalyzed asymmetric synthesis of axially chiral (Allenylmethyl)silanes and chirality transfer to stereogenic carbon centers in SE′ reactions

[GRAPHICS] Novel stereoselective reactions of 4-substituted-1-trimethylsilyl-2,3-butadienes ((allenylmethyl)sildnes)(-) were developed. The axially chiral (allenylmethyl)silanes were prepared from (3-bromopenta-2,4-dienyl)trimethylsilane by a Pd-catalyzed asymmetric reaction with soft nucleophiles with up to 88% enantloselectivity. The (allenylmethyl)silanes reacted with acetals in the presence of a TiCl4 promoter to give 1,3-diene derivatives via an S-E' pathway. The 1,3-dienyl products have (E)-geometry exclusively and up to 88% chirality transfer from the axially chiral allenes to the centrally chiral 1,3-dienes was observed in the SE' reaction.