Cyclic Oxyphosphoranes with Six- and Seven-Membered Rings

Abstract

X-ray and variable temperature NMR investigations of cyclic pentaaxyphosphoranes reveal a preference of six- and seven-membered rings for apical-equatorlal orientations of trigonal bipyramids. Saturated six-membered rings prefer a boat conformation. Apical-equatorial ring pseudorotations are more facile for five-membered rings, whereas ligand exchange via diequatorial ring placement is more facile for the larger rings. Application to enzymatic reactions of cyclic AMP is emphasized.