THE REACTION OF THIOIMIDES WITH PHOSPHORUS YLIDES

The reaction of a series of thioimides with phosphorus ylides, in a manner analogous to the Wittig reaction, has been examined. The resulting reaction products represent potentially valuable intermediates in tetrapyrrole pigment synthesis. In addition to the desired thio-Wittig-type coupling reaction, the presence of two competing reaction pathways, S-alkylation and oxidation/reduction, has been observed with certain substrates. These empirical observations have been correlated to theoretical data, derived from MNDO and ab initio calculations, which delineate the structure-reactivity relationships governing product distribution from the various reaction pathways. A detailed analysis is presented of the mechanisms of the thio-Wittig coupling reaction and the competitive S-alkylation reaction.