Heterocyclics 2,2-dioxides

Other heterocycles which rearrange to isoxazoles are pyridazine 1,2-dioxides (77CC856) and pyridinium salts (80CPB2083), although these transformations are of little synthetic importance. 

A few special syntheses of thiirane derivatives from four-membered sulfur heterocycles are known. Methylenethiiranes are derived by thermolysis of the tosylhydrazones of thietan-3-ones (Scheme 143) (81TL4815), and 2,2,3,3-tetrakis(trifluoromethyl)thiirane is obtained by thermolysis of 2,2,4,4-tetrakis(trifluoromethyl)-l,3-dithietane 1,1-dioxide with loss of sulfur dioxide. 2,2,3,3-Tetrakis(trifluoromethyl)thiirane 1,1-dioxide is obtained in low yield by heating a mixture of 3,3-bis(trifluoromethyl)-l,2,4-oxadithietane 2,2,4,4-tetroxide and bis(trifluoromethyl)ketene. The mono-episulfide of norbornadiene is obtained from thietane derivative (65 Scheme 144) (73JOC649). 

Another heterocyclic molecule that can serve as a benzyne precursor is benzothiadiazole-1,1-dioxide, which decomposes with elimination of sulfur dioxide and nitrogen. ... 

Although thiazole chemistry has been extensively reviewed, 5-oxide and 5,5-dioxide derivatives had not been previously extensively treated. As already cited some aspects appeared regularly in Progress in Heterocyclic Chemistry (Section I). 

Papers dealing with this topic are exhaustively reviewed in Comprehensive Heterocyclic Chemistry I (84CHEC-I(6)235) and II (96CHEC-II(3)373). Nevertheless, little information is available on the 5-oxides. Recently, the heteroaromaticity of thiazole compared with isothiazole and thiadiazole 5,5-dioxide systems was studied (97MI1). Quantum-chemical calculations and X-ray studies were performed on 3,3 -di[l,3-thiazolidin-4-one] derivatives (95JCC(25)589) studied for their potential biological activity (97FA(52)43). 

Thiadiazole 5-oxides and 5,5-dioxides are the least studied among the four possible isomers of thiadiazole system. The main summary is in the first and the second editions of Comprehensive Heterocyclic Chemistry (84CHEC-I(6)447, 96CHEC-II(4)289). Apparently the 5-oxide and the 5,5-dioxide derivatives have not yet been reviewed. There are very few papers in the literature treating these derivatives, and most of these are regarding polycyclic systems. 

Chiral l,2,5-thiadiazolidin-3-one 5,5-dioxides 250 were synthesized by way of conventional methods, with the intention of introducing them in new pseudonucleosides as aglicone (96T(52)993). The synthetic methodology, in accord with previous reports, gave the l,2,5-thiadiazolidin-3-ones in good overall yield (35-55%). The glycosilation was performed on the protected heterocycles to prevent the condensation involving the N-2 atom, the most acidic reactive site. As expected only one anomer was obtained that is the p-one. 

Tautomeric equilibrium in amino-substituted 1,2,6-thiadiazine 1,1-dioxides fused with five- or six-membered nitrogen heterocycles has been extensively studied by Goya and colleagues. No amino group participation in tautomeric equilibria in these systems has been observed. 

Bromo atom of ethyl (3S)-10-bromo-3-methyl-7-oxo-2,3-dihydro-7//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylate was change for hetaryl groups with tributylstannyl derivatives of heterocycles in the presence of (Ph3P)2Pd(II)Cl2 in boiling toluene (OOMIPIO). 7-Aryl-5-oxo-2,3-dihydro-5//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylates, 6-carboxamides and their 1,1-dioxide derivatives were prepared from 7-chloro derivatives in the... 

Crystal and molecular structures of 2,4,4,6-tetraphenyl-4//-thiopyran-1-oxide (143) and the corresponding 1,1-dioxide 141a were investigated to show the boat conformations of the heterocycles as well as an interesting... 

As shown by Heindel and Corley (1979), ring closure also takes place if the nucleophilic nitrogen is part of a heterocycle, as in the diazotization of 5-amino-3-methyl-2-H-l,2,4-benzothiadiazine-l, 1-dioxide (6.50). In the tricyclic compound 6.51 formed initially, the thiadiazinedioxide ring is opened rapidly in water, forming 1-acetyl-7-aminosulfonyl-l-i/-benzo-l,2,3-triazole (6.52). 

A new class of heterocyclic compounds, the 1,2,3,4-tetrazine-l,3-dioxides (6.62) was found by Churakov et al. (1990) on diazotization of 2-tert-butylazoxyaniline followed by oxidation with 3-chlorobenzoic peracid (Scheme 6-42). 

The two principal categories of compounds studied have been diaryl or aryl alkyl sulphones (not dialkyl sulphones, which are polarographically not reducible) and S-dioxides of certain heterocyclic compounds, such as thiophene (also benzo- and dibenzothiophenes) and phenothiazines. The first named have half-wave potentials in the region of — 2.0 V, the thiophene dioxides near — 1.0 V. Some examples of each category may be given. 

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