Behaviour of the hetero-ring in substituted 2-phenylimino-4-thiazolidinones towards the action of organomagnesium compounds

Abstract

Treatment of 5-arylidene derivatives of 2-phenylimino-4-thiazolidinones with Grignard reagents does not open the hetero-ring, the double bond of the lateral chain, the CC bond and the CN bond of Ic, enter into reaction, yielding colourless products, believed to have structure III. On the other hand, 5-benzylidene-3-phenyl-2-phenylimino-4-thiazolidinone (Id) on treatment with Ph Mg Br undergoes addition to the CC bond of the lateral chain with the formation of 5-diphenylmethyl-3-phenyl-2-phenylimino-4-thiazolidinone (IIc). Whereas, the Grignard reagents do not attack the carbonyl group of the thiazolidine ring in Ic and Id, the carbonyl group in 5-methyl-2-phenylimino-4-thiazolidinone undergoes 1,2-addition with Ph Mg Br, followed by loss of water upon hydrolysis of the reaction mixture to yield Va. Elucidation of the structure of the latter has been proved by an independent synthesis. Hetero-ring opening by the action of Ph Mg Br in the thiazolidine system, has been found upon treatment of 5-methyl-3-phenyl-2-phenylimino-4-thiazolidinone with the same reagent, yielding N,N′-diphenylbenzamidine. The discrepancy in the melting points of the 5-arylidene derivatives of 2-phenylimino-4-thiazolidinone and of 3-phenyl-2-phenylimino-4-thiazolidinone is discussed. © 1964.