A New Halogen-Exchange Reaction between Sn–F and Li–X: Selective 1,2- and 1,4-Reductions of α,β-Unsaturated Ketones and Effects of Halogen Substituents on the Regioselectivity of Organotin Hydrides

We have found that halogen-exchange occurs effectively between Sn–F and Li–X (X = I, Br, Cl) in tin hydride reagents. This fact induced a complete change in the regiochemistry in the reductions of α,β-unsaturated ketones 1 with Bu2SnH2–Bu2SnF2 (Reagent A): the use of Reagent A in combination with HMPA performed 1,2-reductions, while the addition of LiI to Reagent A achieved 1,4-reductions. It was demonstrated that the regioselectivity of organotin hydrides greatly depends on the properties of the halogen substituents attached to tin atoms.