Reactions of Other Derivatives

Reactions of Other Derivatives.—Condensation of 2-methyl-benzothiazoles with aromatic aldehydes may be carried out in 50% aqueous sodium hydroxide at room temperature in the presence of triethylbenzylammonium chloride. In some cases the intermediate carbinols are isolable under these conditions. 2-Methylbenzothiazoles undergo the Vilsmeier-Haack reaction to give products [1 R = C( CHOH)CHO] that can be converted into other heterocycles e.g., alkyl- or aryl-hydrazines furnish pyrazoles.  

Photodehydrodimerization of benzothiazole to give 2,2 -bibenzothiazolyl (30% yield) has been carried out in acetonitrile with air, but was unsuccessful in other 

Kister, A. Blanc, E. Davin, and J. Metzger, Bull. Soc. chint. France, 1975, 2297 A. Samat, J. Kister, F. Gamier, J. Metzger, and R. Guglielmetti, ibid., p. 2627 H. Pommier, A. Samat, J. Metzger, and R. Guglielmetti, J. Chim. phys., 1975, 72, 589. 

Studies of the highly reactive 2-aIkoxycarbonyl-benzothiazole iV-oxides (34 R = COaEt) (see Vol. 3, pp. 622, 629) have continued. On treatment with ArNCO or ArNSO, the interesting ethyl l-(arylimino)(S )benzothiazole-2-carboxylates (35) are produced, with evolution of COa or SO2, respectively. In 

The hydrazide of benzothiazole-2-carboxylic acid may be converted into compounds [1 R = C(0)NHNHC(O)Alk, C(0)NHNHC(0)Ar, C(0)NHNH-C(0)NHAlk, C(0)NHNHC(S)NHAlk, or C(0)NHNHC(S)NHAr] by standard procedures. Cyclization of the oxygen compounds with polyphosphoric acid or phosphorus oxychloride, or of the sulphur compounds with red lead or iodine in sodium hydroxide, yields the corresponding 1,3,4-oxadiazole (37 X = O). The 1,3,4-thiadiazoles (37 X = S) may be prepared by treatment of the oxygen compounds with phosphorus pentasulphide or by cyclization of the sulphur compounds with acid. Compounds (38 X = O or S Y = N) may be prepared similarly from benzothiazole-6-carboxylic acid. When compounds [1 R = C(0)NHNHC(S)NHAlk or C(0)NHNHC(S)NHAr] are cyclized with 5% aqueous sodium hydroxide or polyphosphoric acid they yield compounds (37  

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