NMR and stereochemical studies of non aromatic heterocyclic compounds—II : 13C and 31P NMR of 2-methoxy-1,3,2-dioxaphosphorinanes

¹³C and ³¹P chemical shift data for eight 2-methoxy-1,3,2-dioxaphosphorinanes are reported. Examination of pairs of geometrical isomers, which differ only in the orientation of the OMe substituent on P^III, have shown that both the ³¹P and the ¹³C signals of C_4,6 atoms appear 3–4 ppm at higher field when the OMe is axial compared with the equatorial isomer. This observation can be associated with the 1–3 syn diaxial interaction between the phosphorus axial substituent and the axial hydrogens on C_4,6 and should thus constitute, in the future, a supplementary tool for the structural analysis of this kind of compound. Important long range δ effects were observed both on ¹³C and especially on ³¹P chemical shifts. It is suggested that the high field δ_e effects could reflect a direct stereoelectronic interaction between the P atom and the cyclic C-5 atom. This interpretation is supported by a study of the ³¹P…¹³C coupling constants and their stereochemical dependence.