STRUCTURE AND REACTIVITY OF CYCLIC ENEDIOL N-PHOSPHORYLAZOLES AND N-PHOSPHORYLTETRAMETHYLGUANIDINE

Abstract

A series of cyclic enediol phosphorylazoles (CEP-azoles) derived from the 4,5-dimethyl-2-oxo-1,3,2-dioxaphosphole ring system and pyrrole, imidazole, pyrazole, 1,2,4-triazole and tetrazole have been prepared. The structures of CEP-triazole and of the related phosphoramidate CEP-tetramethylguanidine (CEP-TMG) have been determined by X-ray crystallographic analysis and compared with the known structure of CEP-imidazole. The reactions of CEP-azoles and CEP-TMG with alcohols have been studied and compared with the reactions of CEP-esters, CEP-OR¹, with alcohols, R²OH, under catalysis by the azoles or tetramethylguanidine. Relative rates of reactions and differences in product composition are discussed in terms of the formation of an oxyphosphorane intermediate in nucleophilic substitutions at 4-coordinate phosphorus. Differences in reactivities among the CEP-derivatives have been determined from the occurrence and direction of the following reactions: