Intramolecular S N 2 ring opening of cyclic sulfate: 6-exo-tet versus 7-exo-tet cyclization

Intramolecular S N 2 ring opening of trans-cyclic sulfate by in situ generated carboxylate ion, 5-carbon away from the reaction centre, results in preferably 6-exo-tet-cyclization whereas cis-cyclic sulfate gives a mixture of six- and seven-membered lactones. In contrast, when the carboxylate ion is situated six carbon atoms away from the reactive cyclic sulfate centre, no intramolecular cyclization is observed.