Thiadiazolo-- and --pyrimidines

Synthesis.—A variety of 1,3,4-thiadiazoles continue to be produced by well-established methods, generally in connection with biological or medical screening programmes. The methods of preparation include well-tried cyclizations, replacement reactions in the pre-formed heteronucleus, as well as the production of simple functional derivatives. With very few exceptions, the compounds concerned are derived from 2-amino-l,3,4-thiadiazole. 

The standard synthesis of 5-substituted 2-amino-l,3,4-thiadiazoles from thiosemicarbazides and carboxylic acids has been improved by the use of a mixture (3 1) of polyphosphoric acid and concentrated sulphuric acid as the condensing agent the use of either acid alone produces lower yields.  

Yoshina and K. Yamamoto, Yakugaku Zasshi, 1974,94,1312 Chem. Abs., 1975,82,43 108) [2-subst. 5-(3,4-diaryl-2-furyl)-l,3,4-Uiiadiazoles] S. N. Sawhney, J. Singh, and O. P. Bansal, J. Indian Chem. Soc., 1974, 51, 886 [2-, 6-(l,3,4-thiadiazol-2-yl)benzothiazoles] G. S. Goldin, M. V. Maksakova, V. G. Poddubnyi, and A. N. Koltsova, Zhur. obshchei Khim., 1975,45,2661 [2-amino-5-(c )-trimethylsilyl)ethyl-l,3,4-thiadiazole] H. Rochling and G. Horlein, Annalen, 

504 [2-amino-5-(2,2-dichloro-l,l-difluoroethyl)-l,3,4-thiadiazole] I. Saramet, Farmacia Bucharest), 1975, 23, 35 Chem. Abs., 1976, 84, 70208) [4-(2-amino-l,3,4-thiadia20l-5-yl) diphenyl sulphones] I. Simiti and H. Demian, Farmacia Bucharest), 1973, 21, 713 Chem. Abs., 1974, 81, 63 506) [2-amino-5-(2-aiylthiazol-4-yl)-l,3,4-thiadiazoles] F. Russo and M. Santagati, Farmaco, jErf. ScL, 1976, 31, 41 [2-amino-5-(benzothiazol-2-ylVl,3,4-thiadia20Ies]  

Bognar, C. Jaszberenyi, and A. Tokes, Magyar Kim. Folydirat, 1974, 80, 114 (2-aryl 5-(flavan-4-yl) amino-1,3,4-thiadiazoles] E. V. P. Tao, Synth. Comm., 1974, 4, 249 [l-(5-r-butyl-l,3,4-thiadiazol-2-yl)-l,3-dimethylurea] G. Werber, F. Buccheri, and M. L. Marino, J. Heterocyclic Chem., 1975, 12, 581 [2-amino-5-benzoyl-l,3,4-thiadiazoles and A -l,3,4-thiadiazolines]. 

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