Stereochemistry of the acyclic phosphono- and phosphino-thiocyanide isomerisation into corresponding isothiocyanidates

Optically active t-butylphenylphosphinothiocyanidate ButPhP(O)SCN 3 and t-butyl-O-methyl-phosphonothiocyanidate But(MeO)P(O)SCN 7 have been prepared by condensation of the corresponding sulphenyl chlorides > P(O)SCl with trimethylsilylcyanide and isomerised into optically active t-butyl-O-methyl-phos-phonoisothiocyanidates But(MeO)P(O)NCS 8. Chirality at P in and the optical purity of the chiral phosphino (phosphono) thiocyanidates and isothiocyanidates have been determined by chemical correlations. It has been demonstrated that the thiocyanate ion and amine catalysed thiocyanidate-isothiocyanidate isomerisation > P(O)SCN → > P(O)NCS occurs stereospecifically with inversion of configuration at the P center. This result can be rationalized by postulation of a phosphorane intermediate, formed by nucleophilic attack of the SCN- anion on phosphorus, in which thiocyanate and isothiocyanate groups occupy apical positions. In connection with these studies a number of novel optically active phosphorylated derivatives of carbonic acid, > P(O)NHCSNHR, > P(O)NCCl2, > P(O)NCO and > P(O)NHCOOBut, have also been synthesised.