Cyclic organophosphorus compounds. Part 21. Crystallographic and spectroscopic assignments of configuration at phosphorus in 2-chloro-4-isopropyl-5,5-dimethyl-1,3,2λ5-dioxaphosphorinan-2-ones and in 2-methoxy-4-isopropyl-5,5-dimethyl-1,3,2-dioxaphosphorinanes

Abstract

The crystal and molecular structures of cis- and trans-2-chloro-4-isopropyl-5,5-dimethyl-1,3,2λ⁵-dioxaphosphorinan-2-ones have been determined by single-crystal X-ray analyses. In the solid state, these structures possess equatorial and axial phosphorus–chlorine bonds, respectively, with (S)_P and (R)_P configurations. The temperature-independent formation of the cis-phosphorochloridate by chlorination of the thermodynamically more stable 2-methoxy-4-isopropyl-5,5-dimethyl-1,3,2-dioxaphosphorinane suggests that the latter has the trans geometry with the (R)_P configuration. The geometries thus assigned to the diastereoisomeric methyl phosphites are consistent with the ³¹P n.m.r. data for the corresponding 2-selenides.