6-Membered P-Heterocycles: Ring-Condensed 1,3,2-Diheterophosphorinane 2-Chalcogenides

Literature publications (up to the end of 2006) relating to the synthesis, biological significance and conformational behaviour of carbocycle- and heterocycle-condensed six-membered tetracoordinate P(V) 1,3,2-diheterophosphorinanes are reviewed. The replacement of carbon atoms of cyclohexane by P and O and/or N to form 1,3,2-dioxa-, 1,3,2- oxaza- or 1,3,2-diazaphosphorinanes introduces lone pair electrons instead of hydrogens and changes the bond angles and bond lengths, and can thereby lead to significantly different stereostructural preferences of the hetero ring as compared with those of cyclohexane. Although monocyclic 1,3,2-diheterophosphorinanes often exist in a chair conformation in both the solid and solution states, the existence of conformations other than a chair can predominate in some cases for steric and stereoelectronic reasons associated with the presence of bulky groups on the P-containing ring or in polycyclic rigid systems. After a brief account on the most important pharmacological and stereochemical features, involving the configuration assignment and conformation determination of P-diheterophosphorinanes, the present review mainly focuses on the synthesis and stereostructural studies of carbo- and heterocycle-condensed derivatives, where the fused ring may exert considerable effects on the conformational behaviour of the P-hetero ring.