1,2,5-Thiadiazole 1,1-dioxides thermolysis

The thermolysis of o-azidosulfonyl-f-anilines resulted in nitrene formation and trapping of the nitrene by the adjacent amino nitrogen to give a zwitterionic thiadiazole dioxide 108 from the dimethyl- or 6-membered heterocyclic ring precursor. The ring-opened/dealkylated derivative 109 was formed from other dialkyl or ring systems (Scheme 36) [74 JCS(P1)2451]. The pyrrolidino azide was unique in giving no thiadiazole, but rather products derived from a sulfonylnitrene precursor, perhaps in... 

Phenyl-l,3,4-oxathiazol-2-one (370), prepared from primary amides and tri-chloromethanesulfenyl chloride, undergoes a ready thermal elimination of carbon dioxide with the formation of the nitrile sulfide ylide (371). This can be trapped by a wide variety of unsaturated dipolarophiles, and with an alkyne provides a ready route to isothiazoles (372) (see Chapter 4.17). Applications to 1,2,4-thiadiazole synthesis are described in Chapter 4.25. Thermolysis of l,3,4-oxadiazolin-5-ones (500 C/10 mmHg) results in the loss of CO2 and generation of the corresponding nitrilimine (78JOC2037). 

The ready availability of 1,2,5-thiadiazole 1,1-dioxides (177) (see above) has provided data for their comparison with the parent aromatic ring system, The NO-, NN-, and OO-dimethylated derivatives are obtained by suitable alkylation procedures. The action of an excess of phosphorus pentachloride gives the 3,4-dichloro-compound (181 X = Cl), which is rapidly hydrolysed back to the dione (177), and which undergoes ammonolysis or aminolysis to give a variety of 3,4-di(substituted amino)- ,2,5-thiadiazole 1,1-dioxides [e.g. (181 X = NR R )]. The amide-like character of the 3,4-diamino-derivative (181 X = NHa) has been noted, as has a pronounced tendency of the 3,4-di-alkoxy-derivatives (181 X = OMe) to transfer their 0-alkyl groups to the ring nitrogen on thermolysis. ... 

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