The elucidation of the mechanism in operation is further exacerbated by the observation that the reaction proceeds in the absence of both pDTCz-DPmS and HE (entry 7; Table ), although at a low yield of 27%. Based on the UV-Vis absorption spectra (Figure ) of the remaining reactants, only PhCCBr has an absorption band at the excitation wavelength and given that the reaction does not operate in the absence of light (entry 11, Table ), we therefore conclude that photoinduced homolytic cleavage of the C-Br bond must occur to initiate the C(sp)-C(sp 3 ) reaction. Since the reaction also does not proceed in the absence of PC, HE and DIPEA (entry 8; Table ), the addition of DIPEA must be necessary to act as a proton shuttle to form the target product.