Highly efficient and stereoselective route to threo- and erythro-α-allylated α-fluoro-β-hydroxy esters via radical allylation reaction

Treatment of α-bromo-α-fluoro-β-hydroxy esters with trimethylaluminum in dichloromethane, followed by reaction with allylic stannanes and a catalytic amount of triethylborane at −15°C, gave the corresponding threo-α-allylated α-fluoro-β-hydroxy esters in a highly stereoselective manner. On the other hand, the reaction of the β-hydroxy esters with allylic stannanes under the influence of a catalytic amount of triethylborane in tetrahydrofuran or isopropyl alcohol at −78°C proceeded erythro-selectively, leading preferentially to the erythro-isomers of the corresponding α-allylated esters.