Photochemical Metal-Hydride Hydrogen Atom Transfer Mediated Radical Hydrofunctionalization of Dienes and Allenes

The metal-hydride hydrogen atom transfer (MHAT) method is widely recognized as a powerful technique for functionalizing alkenes. However, its application in the functionalization of industrial feedstock dienes and allenes is relatively rare due to challenges related to chemo-selectivity. In recent studies, Co-porphines have been identified as highly efficient catalysts under photoirradiation for MHAT, demonstrating an exceptional level of chemoselectivity for the functionalization of dienes and allenes, while disregarding other simple olefins present. This novel method enables the selective reductive coupling of pyridines with dienes and the allylation of aldehydes by the combination with Ti catalysis. Mechanistic studies and density functional theory (DFT) calculations support the idea that the non-reversible transfer of hydrogen atoms from cobalt hydride to dienes and allenes, leading to the generation of allyl radicals, is the key step in the catalytic cycle.