We report a phosphine-catalyzed trans hydroboration of alkynoate esters and amides. The reaction proceeds under mild conditions with exclusive ( E)-selectivity to afford ( E)-β-boryl acrylates and ( E)-β-boryl acrylamides in good to excellent yields. The reaction is tolerant of a variety of functional groups and allows efficient access to novel oxaboroles as well as a pargyline derivative (MAO inhibitor). Theoretical calculations suggest an internal hydride generates a phosphonium allenoxyborane followed by the formation of a key phosphonocyclobutene intermediate that collapses in a stereoselective, rate-limiting step.

We report a ligand-free copper-catalyzed α-borylation, defluorination of β-substituted, α-trifluoromethyl-α,β-unsaturated esters. The reaction affords geminal-difluoroallyl boronic acid derivatives in moderate to good yield. The reaction was tolerant of various substrates...

A method for the regioselective reduction of the terminal double bond of 1,1-disubstituted allenes has been developed. In the presence of a palladium catalyst, tetrahydroxydiboron and stoichiometric water, allene semireduction proceeds in high yield to afford Z-alkenes selectively.