Stereochemistry of organophosphorus cyclic compounds. Part IV. Synthesis and geometrical isomerism in cyclic five-membered phosphorus thioacids. Crystal and molecular structure of the imidazolium salt of r-2-hydroxy-c-4-methyl-1,3,2-dioxaphospholan-2-thione

Abstract

Several five-membered cyclic phosphorus monothioacid salts have been prepared by treatment of the corresponding cyclic thiophosphoryl chlorides with imidazole and water. The imidazolium salt of 2-hydroxy-4-methyl-1,3,2-dioxaphospholan-2-thione has been found to exist as a mixture of cis and trans isomers separable by crystallisation. The configurations of these diastereoisomers have been assigned on the basis of chemical correlations and X-ray analysis. The cis-isomer (with reference to the ring methyl group and the exocyclic oxygen atom) crystallises in space group P with a= 7.818(5), b= 9.736(5), c= 6.958(5)Å, α= 76.42(20), β= 98.18(20), γ= 97.23(20)°. The structural features of the 1,3,2-dioxaphospholan ring are discussed.