Sulfur-Phosphorus and Selenium-Phosphorus Heterocycles -Synthesis and Structure Elucidation by Modern NMR -Techniques

Abstract

The cis-trans isomerization of the four-membered heterocycle (MeP(S)S)₂ (1), well known as methylperthiophosphonic acid anhydride, has been found to proceed via its eight-membered dimer. This can be concluded from the order of the reaction, the activation parameters, and three intermediates, which were found by DNMR methods to take part in the isomerization process. A new synthetic route to selenium phosphorus heterocycles is offered by the oxidative ring closing reaction of the trimethylsilyl esters of triselenophosphonic acids (6) with bromine or dimethylsulfoxide. The silyl esters have been obtained from the reaction of bis(trimethylsilyl)- organophosphanes with elemental selenium. The structures of the tetraselenadiphosphorinane (MeP(Se)Se₂)₂ (7) and the triselenadiphospholane MeP(Se) Se₂MeP(Se)Se (8) have been elucidated by homonuclear ³¹P double quantum spectra.