Synthesis of β,β-Disubstituted Vinyl Boronates via the Ruthenium-Catalyzed Alder Ene Reaction of Borylated Alkynes and Alkenes

Ruthenium-catalyzed Alder ene reactions between borylated alkynes and terminal alkenes give the corresponding β,β-disubstituted vinyl boronates with high selectivity for the branched isomer. The stereochemistry of the vinyl boronate moiety was the result of a formal trans addition of the ene subunit across the alkyne, which is the opposite stereochemical outcome observed for other internal alkynes.