MECHANISTIC STUDIES IN THE CHEMISTRY OF THIOUREA .3. ACID-CATALYZED REACTION WITH 1-PHENYLPROPANE-1,2-DIONE AND RELATED-COMPOUNDS

Reaction of thiourea with 1-phenylpropane-1,2-dione in the presence of acid results in formation of 4,4'-methylenebis(5-phenyl-4-imidazoline-2-thione) 11c. A mechanism of reaction is proposed, based on intermediates isolated from this and related reactions and on the detection of intermediates by C-13 NMR spectroscopy using labelled reactants. With 1,3-dimethylthiourea the reaction ceases on formation of 1-(1,3-dimethyl-5-phenyl-2-thio-4-imidazolinyl)methyl-1,3-dimethylthiourea 4a and the analogue of this derived from thiourea is proposed as an intermediate in the formation of 11c. The two isomeric N-methyl analogues (11a and 11b) of 11c are obtained on reaction of 1-phenylpropane-1,2-dione with 1-methylthiourea. 1-Phenylbutane-1,2-dione and 1,3-diphenylpropane-1,2-dione react similarly, but 3-methyl-1-phenylbutane-1,2-dione does not react at all.