REACTIONS OF PHOSPHINES WITH ACETYLENES. PART 19.¹ CONFIGURATIONAL AND CONFORMATIONAL ANALYSIS OF 1,2-DIMETHOXYCARBONYL-2-TRIS(CYANOETHYL)PHOSPHONIUM-ETHANE SULPHONATES

Abstract

1,2-Dimethoxycarbonyl-2-tris(cyanoethyl)phosphonium-ethane sulphonates are present in both threo and erythro forms in TFA (trifluoroacetic acid) and DMSO (dimethylsulphoxide). The relative proportions change from a 5 : 1 ratio for a solution in DMSO to a 1 : 1 ratio for a solution in TFA. The predominant conformation in the threo betaine also depends on the nature of the medium-the conformer with the vicinal protons trans predominates in DMSO while that with the ester groups trans predominates in TFA. In contrast the erythro form adopts essentially the same conformation in both solvents.