Use of carbohydrate derivatives for studies of phosphorus stereochemistry. Part I. Stereochemistry of 1,3,2-dioxaphosphorinan-2-ones and synthesis of optically active phosphine oxides

Abstract

Pairs of 1,3,2-dioxaphosphorinan-2-ones, epimeric at phosphorus, have been prepared by treatment of methyl 2,3-di-O-methyl-α-D-glucopyranoside and -galactopyranoside with phosphonic or phosphoric dihalides. The configuration at phosphorus in these derivatives has been assigned on the basis of n.m.r. and i.r. data and of comparison of the rates of formation and relative stabilities of the epimers. For the formation of the 1,3,2-dioxaphosphorinan-2-ones it is suggested that the kinetic preference for the thermodynamically less stable isomers depends on steric interactions in twist-ring transition intermediates, and that the subsequent equilibration depends on the relative stabilities of the chair conformers. The conversions of methyl 2,3-di-O-methyl-α-D-glucopyranoside (R)- and (S)-4,6-methyl phosphonate into (S)- and (R)-ethylmethylphenylphosphine oxide, respectively, by sequential addition of phenylmagnesium bromide and ethylmagnesium bromide provide examples of the utility of carbohydrate 1,3,2-dioxaphosphorinan-2-ones for the stereospecific synthesis of optically active phosphine oxides.