Oxathiazolium olate

Phenyl oxathiazolium-olate (35) and the phosphaalkyne Bu C=P react to yield two isomeric 1,2,4-thiazaphospholes. Besides the main product (36) with the expected order of substituents, 3% of the product (37) with the reversed order is found <87CB1809,88AG1541). 

A heavily substituted non-classical thienol3,4-c]isothiazole (175) has been prepared in almost quantitative yield by the cyclization of the dibenzoylisothiazole (174) with phosphorus pentasulphide (Scheme 15). The precursor (174) is itself synthesized, albeit in low yield, from the oxathiazolium-olate (173), by a process akin to that described earlier (p. 286). The thiophen ring (but not the isothiazole ring) in (175) behaves as a masked ylide, and it undergoes cycloaddition reactions such as with dimethyl acetylenedicarboxylate, when the 2,1-benzisothiazole (178) is... 

Die rontgendiffraklometrische Analyse 1 von 4-Phenyl-1,3,2-oxaihiazolium-5-ulat ergibt Bindungslangen, die den Grenzformeln III und IV am nachsten sind. Das Dipolmoment von 4-Phenyl-1,3,2-oxathiazolium-5-olat wurde zu 4,5 D bestimmt1. 

Die mesoionischen 1,3,2-Oxathiazolium-5-olate reagieren mit durch elektronenziehende Grup-pen aktivierten Alkinen in einer thermischen [3 + 2]-Cycloaddition unter Bildung von 1,2-Thiazolen4-6-9-10 auch die Reaktion mit aktivierten Alkenen4 6 fiihrt iiber einen Dehydrie-rungsschritt zu 1,2-Thiazolen (vgl. Bd. E8a, S. 722)3. 

In ahnlicher Weise iibertragt 4-Phenyl-l,3,2-oxathiazolium-5-olat das C,N,S-Strukturelement auch auf ein stabiles Alkylidin-phosphan15 und auf Benzo-cyclopropen1. ... 

Thiazol 5-(4-Brom-phenyl)-3,4-dimethoxycarbonyl- E8a, 722 (4-Ar— l,3,2-oxathiazolium-5-olat + ROOC — C = C — COOR)... 

From Meso-ionic l,3,2>oxathiazolium-5>olates (Type B).— The photolysis (at 4045—4078 A) of the meso-ionic 4-phenyl-1,3,2-oxathiazolium-5-olate (1) yields, as the final products, benzonitrile, sulphur, and carbon dioxide. The suggested mechanism (1)- (2) (3) (4) receives experimental support from the fact that the ultimate intermediate (4) can be trapped (10%) as the substituted isothiazole (5) by means of dimethyl acetylenedicarboxylate, the alkyne undergoing 1,3-dipolar cycloaddition to the intermediate benzonitrile sulphide." ... 

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