(13) (a) Kise, H.; Whitfield, G. F.; Swern, D. Tetrahedron Lett. 1971, 1761. (b) Dawson, A. D.; Swern, D. J. Org. Chem. 1977, 42, 592. (c) Gassman, P. G.; Parton, RL Tetrahedron Lett. 1977, 2055. (14) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornel1 University Press: Ithaca, New York, 1960; p 224. ... 3 nitrogen atom in 3 is also sp2 hybridized, but the SN bond distance of 1.644 A is considerably shorter than the pre- dicted single-bond ...