An attempt to effect allenic elimination by a thiolate ion in NN-dimethylformamide

Abstract

2-Halogeno-1,1-diphenylpropenes (halogen = Cl or Br), when treated with sodium toluene-p-thiolate in dimethyl-formamide, gave exclusively 1,1-diphenyl-2-(p-tolylthio)propene. The reaction was investigated to determine whether it proceeded via a direct nucleophilic substitution or an elimination to 1,1-diphenylallene followed by nucleophilic addition of thiol to the allenic intermediate. By examining the kinetics and products of the reaction, by searching for deuterium incorporation when the reaction is carried in the presence of p-MeC₆H₄·SD, and by independently studying the addition of thiol to diphenylallene, the allenic elimination–addition mechanism was ruled out. The behaviour of this system in ethanol is briefly compared with that in dimethylformamide.