Anhydro-4-hydroxy thiazolium hydroxide

Reactions of imidazo[2,l-fe]benzothiazoles and imidazo [2,l-b]thiazoles with dibenzoylacetylene (82BCJ200) proceed similarly. Potts and Kane-masa (79JOC3803) found that DM AD and dibenzoylacetylene react with anhydro-3-hydroxy-7-methyl-2-phenylimidazo[2,l-f>]thiazolium hydroxide to give 86, although in poor yield. Probably adducts of type 85 are intermediates. 

Ph, R = H) and acetic anhydride-triethylamine was initially thought to be anhydro-2,3-diphenyl-4-hydroxy-l,3-thiazolium hydroxide, CijHiiNOS (114, R = R = Ph, R = H), but later studies established that the product had the molecular formula C30H24N2O2 and the constitution 116. The synthesis of the meso-ionic l,3-thiazol-4-one (114, R = R = Ph, R = H), orange-yellow needles, m.p. 113°-115°, was successfully achieved by dehydration of the acid (115, R = R = Ph, R = H) using acetic anhydride-triethylamine for a few minutes at room temperature. The acids (115, R = NR2, R = Ph, R = H) and acid anhydrides similarly yield the corresponding meso-ionic l,3-thiazol-4-ones (114, R = NRj, R = Ph, R = H). Analogous polycylic meso-ionic l,3-thiazol-4-ones have also been prepared. ... 

Photolysis (4045-4078 A) of anhydro-5-hydroxy-l,3,2-oxa-thiazolium hydroxide (169, R = Ph) gives benzonitrile (77%), sulfur (> 90%), and carbon dioxide. This reaction has been interpreted as involving the bicyclic intermediate 172, which then transforms via the thiazirin 173 into the thiobenzonitrile oxide 174. The postulated intermediates 172 and 173 are analogous to those proposed (139 and 140) for another photoreaction. The possible involvement of the thionitrile oxide 174 is indicated by its trapping with dimethyl acetylene dicarboxy-late this yields 4,5-dimethoxycarbonyl-3-phenylisothiazole (175). ... 

Thiazol-5-ones (Anhydro-5-hydroxy-lJ-thiazolium Hydroxides) (105)... 

U-Thiazol-4-ones (Anhydro-4-hydroxy-1,3-thiazolium Hydroxides)... 

In 1973 Cava et al. reported the synthesis of 4,6-dimethyl-IH,3H-thieno[3,4-c]thiophene (142)102 and l,3,4,6-tetraphenylthieno[3,4-c]-thiophene (149)103 as well as data on some chemical conversions of the latter and the dehydration of 4,6-dimethoxycarbonyl-l//,3//-thieno-[3,4-c]thiophene sulfoxide. Thienothiophene (149) was also obtained (42%) by Potts and McKeough104 by condensation of anhydro-4-hydroxy-2,3,5-tripheny thiazolium hydroxide with dibenzoylacetylene followed by reaction of the product with P2S5. 

Under basic conditions, mesoionic 1,2,3,4-oxatriazoles 5 and 6 rearrange in alcohol solutions to the respective anhydro-5-hydroxy-thiatriazolium hydroxides and anhydro-5-hydroxy-tetrazolium hydroxides (Equation 2) <1979J(P1)732, 1996CHEC-II(4)679>. That rearrangement of 1,2,3,4-oxatriazole 5 (Ar = Ph) to 3-phenyl-5-anhydro-l,2,3,4-thiazolium hydroxide can be induced electrochemically, has been reported for the first time (Section 6.08.5.5) <1997MRC124>. 

Cycloaddition chemistry of anhydro-4-hydroxy-l,3-thiazolium hydroxides (thioisomunchnones) for the synthesis of heterocycles , Padwa, A.,... 

Cycloaddition chemistry of anhydro-4-hydroxy-l,3-thiazolium hydroxides (thioiso-munchnones) for the synthesis of heterocycles , Padwa, A., Harring, S. R., Hertzog, D. L., and Nadler, W. R., Synthesis, 1994, 993. 

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