Synthesis and Properties of 4- Selenadiazoles

Lalezari s synthesis of 1,2,3-selenadiazoles (these Reports, Vol. 2, p. 720) has been extended to the production of cycloalka-1,2,3-selenadiazoles (30 n = 3—6 or 10) from cyclic ketone semicarbazones (29). Their pyrolysis yields the acetylenes (31) (e.g. cyclo-octyne) and dimeric selenohydrocar-bons of type (32). Almost identical results were reported independently by another group. The method is also applicable to the synthesis of 

The thermolysis and photolysis of 4-ethoxycarbonyl-l,2,3-selenadiazole (34) and its 5-methyl derivatives have been briefly reported and their 

Alkalis convert 4-substituted 1,2,3-selenadiazoles, with evolution of nitrogen, into equilibrium mixtures of cis- (35) and trans- (36) 2, o -disubsti-tuted 1,4-diselenafulvenes, presumably by the mechanism shown. The 

7-Amino-l,2,3-benzothiadiazoles can themselves undergo this rearrangement. Thus, diazotization followed by reduction with hypophosphorous acid converts 7-amino-6-chloro-4-methyl-l,2,3-benzothiadiazole (40) into the rearranged 4-chloro-6-methyl compound (41) a small but significant quantity of non-rearranged product (42) is also obtained. When C-4 is 

Diazonium salts derived from 7-aminobenzisothiazole (43) similarly yield l,2,3-benzothiadiazole-7-carbaldehyde and analogues (44) on decomposition under Sandmeyer conditions. Reduction of the diazonium group by hypophosphorous acid produces, without rearrangement, the benziso-thiazole (45).  

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