1,3,2-Oxazaphospholidines from (–)-ephedrine. Intermediates for the stereospecific synthesis of optically active dialkyl alkylphosphonothioates and -selenoates, trialkyl phosphoro-thioates and -selenoates, dialkyl methylphosphonates, and trialkyl phosphates

Abstract

The configurations of the cis- and trans-isomers of 2-substituted 1,3,2-oxazaphospholidin(e)-2-ones, -2-thiones, and 2-selones derived from (–)-ephedrine have been established by spectroscopic and chemical methods. Displacements of the exocyclic 2-substituents occur with retention of configuration at phosphorus. With sodium alkoxides, the 1,3,2-oxazaphospholidine ring is opened by P–N rather than P–O bond cleavage, and inversion of configuration at phosphorus is observed. Under basic conditions the 2-methylamino-1-phenylpropyl phosphates derived from (–)-ephedrine rearrange to afford aziridines and phosphoric acid derivatives; in the cases of the sulphur- and selenium-containing derivatives optically active phosphorus thioacids and phosphorus selenoacids are formed and can be isolated as SMe and SeMe derivatives. These latter derivatives are converted into O-alkyl derivatives on treatment with alcohols in the presence of alkoxides or bromine or silver nitrate, and the stereoselectivities of these reactions have been determined. The optical purities of the title compounds have been measured by an n.m.r. method using chiral shift reagents.