CYCLIC OXYPHOSPHORANES

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Abstract
A review on pertinent information on cyclic oxyphosphoranes is presented. Recent X-ray structures and variable temperature 1H NMR investigations of cyclic pentaoxyphosphoranes reveals a preference for a boat conformation for saturated six-membered rings in apical-equatorial orientations of trigonal bipyramids. These studies include five-, six-, and seven-membered rings and show that the solid state structures are retained in solution. 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. The importance of the apical-equatorial ring orientation for phosphorinanes appearing as trigonal bipyramidal intermediates in enzymatic reactions of cyclic AMP analogs is emphasized.