From Oxathiazolones

From Oxathiazolones (Type B).—3-Phenyl-l,2,4-oxathiazol-5-one (17) is decomposed thermally to benzonitrile and sulphur, but condenses with activated dipolarophiles to yield 1,3-dipolar adducts that may arise from the intermediate benzonitrile sulphide (18). Thus, interaction of the oxathiazolone (17) and dimethyl acetylenedicarboxylate in chlorobenzene at 130 °C produces dimethyl 3-phenylisothiazole-4,5-dicarboxylate (19) in excellent yield. The use of ethyl propiolate (HC=CCOaEt) similarly affords the expected isomeric esters (20) and (21), each in 35% yield. The... 

From Oxathiazolones (Type B).—A kinetic examination of the synthesis of 3-phenylisothiazole-4,5-dicarboxylate from 5-phenyl-1,3,4-oxathiazol-2-one and dimethyl acetylenedicarboxylate (these Reports, Vol. 2, p. 558) supports the intermediacy of benzonitrile sulphide. The method is also applicable to alkyl analogues. ... 

Rhodium(II) catalyzed the addition of the carbene formed from methyl diazoacetoacetate, to the oxathiazolone (112 R = 4-MeOQH4) gives the 1,4,3-oxathiazine derivative (113) in low yield (6%), this probably proceeds through the intermediate sulfonium ylide (114), by decarboxylation and ring closure, either concominantly or sequentially (Scheme 14) <90JCR(S)343>. 

Phenyl nitrile sulfide, from the thermolysis of an oxathiazolone (34) (R = Ph), adds with the same orientation as the nitrile oxides to Bu C P (Scheme 10) <87S689, 88AG1541>. More 1,2,4-thiazaphospholes are produced with phosphaalkenes, R = Ph, 2- and 4-tolyl, R = Ph, SiMe3 <88TL4535> for side products of this reaction see Chapter 3.15 and Section 4.22.11.2. 

The mesoionic 1,3,2-oxathiazolone (12 Ar = Ph) in fact, gives photo products resulting from two different pathways (Scheme 7). Path B via phenylthiazirine (66) predominates with light of wavelength 400 nm in benzene (81LA1025), whereas in ethanol reversible... 

Nitrile sulfides are well suited for the synthesis of isothiazoles incorporating the C=N-S unit via their 1,3-dipolar cycloaddition reactions with double or triple-bonded dipolarophiles. Benzonitrile sulfide 210 is readily prepared from decarboxylation of oxathiazolone 209 using microwave irradiation <05SC807>. Subsequent cycloadditions to dimethyl acetylene-dicarboxylate (DMAD) and dimethyl fumarate afford 211 and 212, respectively. In the case of ethyl propiolate, a 1 1 regioisomeric mixture of phenylisothiazoles 213 and 214 is obtained. 

Mechanistically, a carbenoid, obtained via rhodium-catalyzed decomposition of the diazo compound, should form the sulfur ylide 5 from the oxathiazolone 4. This yields the oxathiazine 7 by ring opening, loss of carbon dioxide and recyclization, possibly via the ylide 6. 

The formation of 1,3,5-triphenylpyrazole by peroxy-acid oxidation of the pyrazoline (683) can be considered as a dehydration of the intermediate oxaziridine (684). The elusive thiaziridine moiety (686) has been proposed to account for the formation of benzonitrile and sulphur from photolysis of the mesoionic oxathiazolones (685). Diaziridine intermediates (688) and (690) have been suggested to account for the products in photolysis... 

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