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Synthesis of N-containing annelated 1,2,3-thiadiazoles: heterocyclization of thioamide derivatives

Vasily Bakulev, Vera Berseneva, Yury Morzherin, Natalia Belskaya and Marina Muhacheva

Department of Organic Synthesis Technology, Ural State Technical University, 620002 Ekaterinburg, Russia

We have studied the direction of the cyclization of N,N'-disubstituted malondithioamides 1 into isomeric 5-amino-1,2,3-thiadiazoles 2 and 3. It has been shown that the ratio of isomeric heterocycles 2 and 3 depends on their relative stability. The ratio of thiadiazoles 2 and 3 in the mixture is also influenced by the solvent.

In order to prepare new heterocyclic sulfur compounds a systematic study of the reactions of thioamides 4-6 with acetylenedicarboxylates and propiolates has been carried out. These reactions were found to take place in three directions to form thiazine derivatives of types 7 and 9, thiazoles 8 and allylmercapto imidazoles 10.

We have shown that the direction of these reactions depends on the nature of thioamide and on the type of acetylene derivative used.

A number of hydrazonoyl thioamides 11 have been prepared to study their oxidative cyclization. It has been shown that their reaction leads to the formation of 2-aryl-1,2,3-thiadiazolidene-5-imines 12, 13.