Stereoselective formation of a 3,5-trans-disubstituted 1,4-tetramethylene-(tetrahydro-2,2-furylidene)ammonium salt in bromination of 2-phenylthiopent-4-enoic acid dialkylamide

The reaction of N-(2-phenylthiopent-4-enoyl)pyrrolidine with bromine results in the stereoselective formation of 1,4-tetramethylene(5S^*-bromomethyl-3R^*-phenylthiotetrahydro-2,2-furylidene)ammonium bromide.