Tandem Reactions Enable Trans- and Cis-Hydro-Tertiary-Alkylations Catalyzed by a Copper Salt

A methodology to synthesize <i>trans</i>- and <i>cis</i>-alkenes via well-controlled hydroalkylation of alkyl radicals to alkynes is reported. α-Bromocarbonyl compounds are useful alkyl radical precursors in the presence of Cu­(I) catalysts. Under copper catalyst conditions and in the presence of silane or alcohol/B₂pin₂, trans- and cis-hydroalkylation occurred with excellent stereoselectivities. The judicious choice of additives allowed for this stereodivergence, giving selective access to the trans-alkylated alkenes with HSiTMS₃ and cis-alkylated alkenes with <i>t</i>-BuOH/B₂pin₂ in good yields with selectivities