Reactions of Meso-ionic Thiazoles

Reactions of Meso-ionic Thiazoles. The meso-ionic thiazole (43 = Ph, R = 

Reactions of Meso-ionic Thiazoles.—This has been one of the major areas of development in thiazole chemistry during the period under review. A full account has appeared (see Vol. 3, p. 449) of the synthesis of 3,4-dibenzoyl-2,5-diphenylthiophenfrom dibenzoylacetylene and flwA //ro-4-hydroxy-2,3,5-triphenyl-thiazolium hydroxide (12 R = = R = Ph). This meso-ionic compound 

4-triphenyl-3(2/f)-isoquinolone by extrusion of sulphur. Approximately equal amounts of two isolable adducts (49) and (50) are formed with dimethyl 7-oxabicyclo[2,2,l]hepta-2,5-diene-2,3-dicarboxylate. Adduct (50) may be used to prepare thiophens or pyridones. Meso-ionic thiazole (14 Ri = R3 =z Ph, R3 = Me) similarly reacts with this bicyclic diene to give non-isolable adducts, which decompose with elimination of a furan and carbonyl sulphide to give pyrroles. With various 2,3-diphenylcyclopropenylidenes it gives adducts [51 X = O, S, NTs, C(CN)2, or C(CN)C02Et], which also extrude carbonyl sulphide with concomitant ring-expansion and formation of a pyridine.  

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