We report a phosphine-catalyzed hydroboration of primary and secondary propiolamides. In the presence of stoichiometric pinacolborane and catalytic n-tributylphosphine, a variety of propiolamides were successfully converted to their respective cinnamamides in excellent yield with (E)-selectivity. The reaction condition is tolerant of various functional group such as alkene, alkyne, ketone, or ester to achieve the chemoselective reduction of the propiolamide. We performed deuterium labeling studies and trapping of a β-phosphonium intermediate to confirm regiochemistry of the organophosphine catalyst to support the proposed mechanism. Furthermore, DFT calculations revealed a clear energetic driving force for the (<i>E</i>)-cinnamamide over the (<i>Z</i>)-isomer.

Organocatalytic semireduction of primary and secondary propiolamides: Substrate scope and mechanistic studies

ACS Spring Meeting 2021

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