At the outset, difunctionalization of the aliphatic alkyne (1a) was investigated . This alkyne (1a) is one of the most challenging substrates for radical-mediated alkyne difunctionalization and has never been used in such transformations. The existing Obenzylic C-H bonds with relatively low bond dissociation energy (BDE = 79.8 kcal/ mol) could serve as hydrogen donor in a 1,5-HAT and could affect the functionalization of an alkenyl radical, leading to undesired hydrofunctionalization products. In fact, DFT calculations indicated that the alkenyl radical intermediate has a strong tendency (ΔG = -23 kcal/ mol) to abstract an H-atom from the benzylic site. The reaction of 1a with a sulfone (2a) using fac-Ir(ppy)3 as photosensitizer and acetone/H2O as co-solvent under green light (510 nm wavelength) irradiation led to a good yield of the allylic alcohol (3a) with exclusive E-configuration (E/Z > 20:1, entry 1). A brief survey of reaction parameters in terms of photocatalyst, solvent, additive and light source was carried out (for details, see the Supporting Information -SI). Replacement of the photocatalyst by other catalysts did not improve the reaction outcome (entries 2-6). Sodium acetate was used to neutralize the hydrobromic acid that was generated in the reaction, and a decreased yield was obtained in the absence of this base (entry 7). Control experiments showed that photocatalyst and light were crucial to the transformation (entries 8-9), and the hydroxyl group in 3a was derived from water. The amount of water in the cosolvent appears to influence the reaction (entries . Reducing the reaction temperature slowed down the reaction rate and sharply decreased the yield (entry 13). Fig. . Optimized reaction conditions: 1a (0.4 mmol), 2a (0.2 mmol), fac-Ir(ppy)3 (1 mol%) and NaOAc (0.1 mmol) in acetone/H2O (2 mL/0.6 mL), irradiated with 30 W 510 nm green LED (5 cm away from the light) at rt under N2 for 72 h. [a] Yields of isolated products are given. [b] 0℃.