1,3-Brook Rearrangement of α-Silyl Allylic Alcohols: Copper-Catalyzed Enantiospecific Formation of Allenes and Copper-Mediated ipso-Substitution Reactions Affording Trisubstituted Alkenes.

A novel and convenient set of conditions is reported for the generation of alkenylcopper reagents via 1,3-Brook rearrangement of alkenylsilane derivatives formed by ruthenium catalyzed trans-hydrosilylation of propargyl alcohol derivatives. The reactive intermediates can evolve in a stereospecific manner into allenes; this new approach is catalytic in copper and proceeds with faithful chirality transfer from the stereocenter of the substrate to the axially chiral product. The overall stereochemical course resulting from trans-hydrosilylation followed by an anti-elimination step is complementary to that of most protocols for allene synthesis starting from propargylic alcohols known in the literature. Alternatively, the transient organocopper species can be intercepted with a variety of electrophiles to give a wide range of substituted alkene derivatives. In this latter embodiment, the sequence of hydrosilylation/Brook rearrangement presents an opportunity for regioselective net trans-hydrofunctionalization of alkynes, a field that has so far been dominated by less benign organotin chemistry.