Thiazole 4.5- dimethyl-2-nitro

Reduction of 2.4-dimethyl-5-nitrothiazole with activated iron gives a product that after acetylation yields 25% 2.4-dimethyl-5-acetamido-thiazole (58). The reduction of 2-methyl 5-nitrothiazole is also reported (351 to give a mixture of products. The nitro group of 2-acetylhydrazino-5-nitrothiazole is reduced by TiCl in hydrochloric acid or by Zn in acetic acid (591. 

Azine approach. The parent cation and substituted derivatives are available by acid-catalyzed cyclization of 2-/3-oxoalkylthiopyridines (401) using an acid such as sulfuric, phosphoric or PPA. Chloro or nitro substituents in the pyridine ring do not seriously interfere (66JHC27). The cyclization of 3-hydroxypyridine analogues (402) is also at the nitrogen to yield the thiazole derivatives. The cyclization, however, is sensitive to the peri interaction between 3- and 5-substituents. In 3,5-dimethyl derivatives (403 R2 = R3 = Me) the steric repulsion is apparent by the unusually low field signals for the methyl protons <81H(15)1349>. 

Thiazol-3-oxid 4,5-Dimethyl-2-[2-(5-nitro-2-furyl)-ethenyl]- E8b, 207 (N - NO)... 

Bis-[l,3-Benzothiazol-2-ylthio]-organo- 997 Bis-[4-tert.-butyl-1,3-thiazol-2-yl]- 71 Bis-[l,3-dimethyl-lH-pyrazol-5-yl]- 557 Bis-[4,5-diphenyl-l,3-thiazol-2-yl]- 71 Bis-[4-methyl-l,3-thiazol-2-yl]- 71 Bis-[5-nitro-l,3-thiazol-2-yl]- 244 Bis-[l,3-thiazol-2-yl]- 70, 71 Ethyl- 337... 

Ami no-2,4-dioxo-6-methyl-hexahydro- 557 4,6-Dimethyl-2-(4-ethyl-5-nitro-l,3-thiazol-2-ylthio)- 294... 

As in the case of oxazoles, the pyridine-like N-atom makes electrophilic substitution reactions more difficult. Thus thiazole does not react with halogens. Donor substituents enhance the reactivity, e.g. 2-methylthiazole reacts with bromine to give 5-bromo-2-methylthiazole. Thiazole cannot be nitrated. 4-Methylthiazole reacts slowly to yield the 5-nitro compound, 5-methylthiazole even more slowly to give the 4-nitro compound, but 2,4-dimethylthiazole reacts fastest producing 2,4-dimethyl-5-nitrothiazole. Sulfonation of thiazole demands the action of oleum at 250°C in the presence of mercury(II) acetate, and occurs at the 5-position. Acetoxymercuration of thiazole with mercury(II) acetate in acetic acid/water proceeds stepwise by way of the 5-acetoxymercury compound and the 4,5-disubstituted product to 2,4,5-tris(acetoxymercury)thiazole. 

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