Oxathiazine 2,2-dioxide

On heating with electron-rich 27r-components such as enamines or ethoxyacetylene, the 1,2,5-oxathiazine 2,2-dioxide (119) gives products which are formally derived by electrocyclic elimination of H2C=S02, followed by [4 + 2] cycloaddition of the resulting diene as shown in Scheme 4 (69IZV2059). 

CSI (57) also adds to alkynes at RT to yield 1,2,3-oxathiazine-2,2-dioxides (71) (Scheme 35). The initial adduct (72) probably undergoes ring-opening... 

A C-C double bond was also formed on reaction of dicydopropylacetylene with chlorosulfonyl isocyanate. Conceivably a [2-1-2] cycloaddition took place to give an unstable product that rearranged to 6-chloro-4,5-dicyclopropyl-l,2,3-oxathiazine 2,2-dioxide in 96 /o yield. ... 

A synthesis of this fused oxathiazine 2,2-dioxide is shown in Section II.2 [2741]. 

Addition to aromatic ketones An extensive study of the reaction of CSI with aromatic ketones (1) presents evidence that the first step is formation of a 3-keto carboxamide (2), which can react with another molecule of CSI to form a malonamide (3). Generally, however, (2) reacts with CSI to form, after reductive hydrolysis with sodium sulfite, either an oxathiazine 2,2-dioxide (4) and/or an oxazinedione (5). The ratio of (4) to (5) depends on the keto-enol equilibrium of the intermediate (2) and on the reaction conditions. 

The 4-oxo-l,2,3-oxathiazine 2,2-dioxides (418), known to be formed from ketones R COCH2R and FSI (FSI is FSO2NCO), can be chlorinated to afford the 4-chloro-derivatives (419). The attack of nucleophiles upon these latter compounds occurs at the 6-position, giving /3-functionalized acrylonitriles (420) and (421) (20—60%) the cis trans ratio varies from 0 100 to 95 5 (Scheme 164)." °... 

Oxathiazine 2,2-dioxide 108 reacted at C(6) upon treatment with several nucleophiles to afford enantiopure a-amino acids 109 (Equation 20) <20010L2965>. 

Erom the various methods reported for the preparation of 1,2,3-oxathiazine 2,2-dioxides, the intramolecular amidation of sulfamates catalyzed by rhodium and silver (Equations 47 and 48) reveals itself as the best approach, in view of the high yields. 

In the reaction of acetylenes with halosulfonyl isocyanates (X = F,C1) 6-halo-l,2,3-oxathiazine-2,2-dioxides 57 are obtained. Rearrangement of the initial [2+2] cycloadduct to an imino ketene, followed by cyclization, accounts for the formation of 57. With two... 

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