P/N Heteroleptic Cu(I)-Photosensitizer-Catalyzed Deoxygenative Radical Alkylation of Aromatic Alkynes with Alkyl Aldehydes Using Dipropylamine as a Traceless Linker Agent

A deoxygenative radical alkylation of aromatic alkynes with alkyl aldehydes for the preparation of allylarenes has been successfully achieved. This transformation is accomplished through the reaction of alkyl aldehydes with alkynes in the presence of dipropylamine and Hantzsch ester catalyzed by a P/N heteroleptic Cu(I)-based photosensitizer under photoredox catalysis conditions. Preliminary mechanistic studies reveal that this aldehyde-alkyne coupling process comprises a regioselective radical addition of in situ-generated alkyl-substituted alpha-amino radicals to alkynes with subsequent 1,5-proton transfer, C-N bond cleavage, and concomitant isomerization of the resulting allyl radical species. Thus, in net result, dipropylamine serves as a traceless linker agent for the deoxygenative radical cross-coupling of alkyl aldehydes with alkynes under photoredox catalysis reaction conditions.