Abstract
Efficient and highly diastereo- and enantioselective conjugate additions of phenyldimethylsilyl units to acyclic and cyclic dienones and dienoates are disclosed. The C-Si bond forming reactions are catalyzed by 2.0-2.5 mol % of a copper complex of a chiral monodentate N-heterocyclic carbene; the requisite reagent, PhMe(2)Si-B(pin), is commercially available or can be easily prepared. Transformations generate allylsilanes in up to 98% yield and >99:1 enantiomeric ratio, and proceed with complete 1,4-selectivity, unless the dienone or dienoate carries a trisubstituted alkene conjugated to the carbonyl group; in the latter cases, 1,6-addition products are obtained exclusively and in up to >98% Z selectivity.