Nucleophilic displacement reactions on the new acyl system, 1-bromo-1-(alkyl- or arylthio)-4-aryl-2,3-diazabuta-1,3-diene

Abstract

Reaction of 1,1-dibromo-4-aryl-2,3-diazabuta-1,3-dienes (1,1-dibromoazines) with aliphatic or aromatic thiols yielded products resulting from thiolysis of one or two bromine atoms. The monobromoazine (1-bromo-1-alkylthio-4-aryl-2,3-diazabuta-1,3-diene) is very reactive undergoing replacement of bromine by primary and secondary amines, phenylhydrazine, water, azide ion, alcohols, and phenols to give a variety of novel thiodiaza-systems. The kinetics of displacement by water has been studied in detail in 40% dioxan at 25°. The effect of substituents on the S–Ar ring (ρ=–1·0) is consistent with thioazacarbonium-ion formation as is the observation of a large solvent effect and rate enhancement by the presence of salts other than those containing bromide ion (which causes a rate depression). Direct S_N2 displacement of bromide ion is also rendered unlikely by the fact that hydrolysis is slightly slower at high hydroxide ion concentration.