Nickel-catalysed SET-reduction-based access to functionalized allenes via 1,4-carbohydrogenation of 1,3-enynes with alkyl bromides

The single-electron-transfer reduction-based radical–polar crossover process has emerged as a useful and powerful strategy for the development of new synthetic transformations. Herein, using SET reduction as the key process, a new nickel-catalysed protocol for the preparation of trisubstituted allenes has been successfully developed via the reactions of enynes with radicals generated from alkyl bromides. According to the results of the deuteration experiment, a mechanism based on the nickel-catalysed reductive radical–polar crossover process has been proposed. The synthetic application of allene has also been demonstrated.