ChemInform Abstract: Thiadiazolium Ylides: Substituted 2H-1,3,5-Thiadiazines and 1,4,5-Trisubstituted-imidazoles from 1,2,4- and 1,2,5-Thiadiazolium-2-unsubstituted Methanide (Ylide) Systems: Ring Expansions and Ring Interconversions via Sulfur-Nitrogen Heterotriene Intermediates. Mechanistic ab initio Calculations. Azolium 1,3-Dipoles.
✍ Scribed by Richard N. Butler; Martin O. Cloonan; John M. McMahon; Luke A. Burke
- Publisher
- John Wiley and Sons
- Year
- 2010
- Weight
- 33 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0931-7597
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✦ Synopsis
Substituted 2H-1,3,5-Thiadiazines and 1,4,5-Trisubstituted-imidazoles from 1,2,4-and 1,2,5-Thiadiazolium-2-unsubstituted Methanide (Ylide) Systems: Ring Expansions and Ring Interconversions via Sulfur-Nitrogen Heterotriene Intermediates. Mechanistic ab initio Calculations. Azolium 1,3-Dipoles.
-Reaction of thiadiazoles (I) and (VI) with silylmethyl triflate (II) affords the corresponding 2-azolium salts, which under desilylation conditions, undergo ring expansion to thiadiazines (IV) and (VII), respectively. In the presence of sodium ethoxide, sulfur is extruded to provide 4-unsubstituted imidazole derivatives (V). In contrast, the azolium salt derived from thiadiazole (VIII) and silylmethyl triflate (II) undergoes spontaneous sulfur extrusion to provide 2-unsubstituted imidazole derivatives (IX) under desilylation conditions. The reaction mechanism is studied in detail.