STEREOCHEMISTRY OF CYCLIC ORGANOPHOSPHORUS COMPOUNDS‐XVI.¹ SYNTHESIS AND THE CRYSTAL AND MOLECULAR STRUCTURE OF meso-BIS-(4,6-DIMETHYL-2-THIO-1,3,2-DIOXAPHOSPHORINANE-2-YL)-OXIDE DERIVED FROM RACEMIC PENTANE-2,4-DIOL

Abstract

4,6-Dimethyl-2-chloro-1.3,2-dioxaphosphorinane-2-thione 5 and the tetramethylammonium salt of 4.6-dimethyl-2-oxo-1.3.2-dioxaphosphorinane-2-thione 4 were prepared from racemic pentane-2,4-diol. Their condensation was found to give a mixture of two diastereoisomeric bis-(4,6-dimethyl-2-thio-1.3.2-dioxaphosphorinane-2-yl)-oxides 3C: racemic and meso-form. The crystal structure of the latter has been determined by the direct method and refined by least-squares to R=0.072, monoclinic space group P2₁/n, a=13.542(3), b=11.175(1), c=10.731(2)Å, β=94.81(1)°. Both dioxaphosphorinane rings adopt chair conformations flattened at phosphorus and the carbon atom C(5). The thiophosphoryl sulphur atoms are in equatorial positions whereas the bridging oxygen atom is axial. Two methyl groups on C(4) and C(6) in each dioxaphosphorinane ring occupy an axial and equatorial position, respectively.