Photocatalytic Umpolung Synthesis of Nucleophilic π‑Allylcobalt Complexes for Allylation of Aldehydes

The concept of “umpolung” reactivity of π-allylmetal complexes has been developed as a powerful method for the allylation of aldehydes. This paper describes the photocatalytic umpolung strategy for the synthesis of nucleophilic allylcobalt complexes through a single-electron-transfer (SET) process. This strategy enables the metallaphotoredox allylation of carbonyls with allyl acetate using organic N,N-diisopropylethylamine as the terminal reductant bypassing the use of a stoichiometric amount of metals. Ultraviolet–visible spectroscopy was used to monitor the redox changes of cobalt in the reaction.