trans-Hydroboration of Propiolamides: Access to Primary and Secondary (E)-β-Borylacrylamides.

A base-mediated trans-hydroboration of propiolamides that provides access to previously elusive primary and secondary (E)-β-borylacrylamide products has been developed. In the presence of n-butyllithium and pinacolborane, complete regioselectivity and stereoselectivity is observed, affording the corresponding vinylboronate products in up to 91% yield. A wide variety of primary and secondary amides served as efficient substrates for this transformation. A plausible reaction mechanism that involves substrate-assisted activation and a key intramolecular cyclization is discussed.