5-Aryloxy-1,2,3-thiadiazoles

ESR spectra of the radical anions of 3-phenoxy-, 3,4-diphenoxy-, and 3,4-dichloro-l,2,5-thiadiazole and of the radical cations of various 3-aryloxy-4-morpholino-l,2,5-thiadiazoles have been obtained by the electrochemical generation of the ions in 3 x 10-3M solutions of the thiadiazoles in the system MeCN/Et4NC104 (ca. 0.1 M) on a platinum helix electrode directly in an ESR resonator at first wave potentials <2003RJC806>. 

Graubaum et al. studied the reaction of 5-aminothiatriazole (10) with chloroformates in the presence of base and isolated 1,2,4-thiadiazoles (104 R = OR) <89M997, 90JPR208). In the reaction between 5-aminothiatriazole and chlorothioformates in the presence of base the main products were trithiapentalenes (116) (Scheme 21). However, in the absence of base the intermediary 5-alkoxy-and 5-aryloxy-3-imino-A -1,2,4-dithiazoline (115) hydrochlorides are isolated. These reactions are analogous to those of (10) and acid chlorides (Section 4.19.6.1.2). 

A number of phenolic ethers of this series show the expected properties. 5-Amino-3-ethoxy-l,2,4-thiadiazole is considerably more soluble in water than its 3-methoxy homolog (3.24 and 0.76 g/100 ml, respectively).88 Their ultraviolet spectra resemble those of the 3-alkyl (or aryl)-5-amino-l,2,4-thiadiazoles.88 3-Alkoxy(or aryloxy)-l,2,4-thiadiazoles are more sensitive towards acids than are the 3-alkyl(or aryl) analogs.88... 

Heating solutions of 5-aryloxy-l,2,3-thiadiazoles 82 (X = O) in DMF at 100 °C in the presence of excess sodium hydride afforded 1,4-benzoxathiins 84 (X = O). The transformation was proposed to proceed via initial cleavage of the thiadiazole ring with subsequent N2 elimination to give the intermediate 83. Subsequent intramolecular rearrangement of intermediates gave the 1,4-benzoxathiins 84 (X = O) <02H483>. 

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