Lalezari cyclization

The Hurd-Mori cyclization and Lalezari cyclization of a-methylene ketones are by far the most widely used routes to 1,2,3-thiadiazole and 1,2,3-selenodiazole, respectively.This approach has been applied in the synthesis of a variety of 1,2,3-thiadiazoles 129 (13JHC630) andl31 (13OT4038) from the corresponding hydrazones. Thiadiazoles 132, derived from 131, can be effectively converted to benzothiophene derivatives (see Section 5.5.4.2). 

Applications of Lalezari and Hurd-Mori reactions are also highlighted in the synthesis of a new class of 1,2,3-selenadiazoles 243 and 1,2,3-thiadiazoles 244 <07JHC1165>. Reaction of sulfonylacetate 241 with semicarbazide 237 gives semicarbazone 242, and oxidative cyclization of 242 with selenium dioxide in acetic acid at 60-70 °C furnishes selenadiazole 243. Compound 242 also undergoes Hurd-Mori reaction with excess thionyl chloride to give thiadiazole 244. 

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