Isothiazoles oxathiazole synthesis

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). 

Synthesis of Isothiazoles from l,3,2-Oxathiazol-5-ones (Type B S-N—C + C-C). The thermal reaction of meso-ionic l,3,2-oxathiazol-5-one [4 R =2,3,4-(MeO)3CeH2] with dimethyl acetylenedicarboxylate (DMAD) at 80 C with CO2 evolution gives 80% of isothiazole (5 R the same) (Scheme 1). ... 

The single example of this class that is known so far (555) has been synthesized as a stable precursor for the thermolytic in situ production of the allonoylnitrile A -sulfide 556 the latter is the reactive species in the synthesis of isothiazole (Section XI Scheme 149) and 1,2,4-thiadiazole C-nucleosides (Section XIX Scheme 203). The 5-(tri-0-benzoyl-/3-D-ribofuranosyl)-l,3,4-oxathiazol-2-one (780) was obtained from the 2,5-anhydro-D-allonic acid amide 779 by heating with chlorocarbonylsulfenyl chloride (84JOC2165 91MI21) (Scheme 213). 

Isothiazoles, Isoselenazoles, and Isotellurazoles Synthesis.—Several new methods for the synthesis of isothiazoles and benziso-thiazoles have been reported. Nitrile sulphides are probable intermediates in one such synthesis they are produced by the thermolysis of l,3,4-oxathiazol-2-ones... 

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