1.2- Benzisothiazole 5- hydroxy

Hydroxy and mercapto substituents at the 3- and 5-positions can also exist in tautomeric forms (see Section 4.01.5.2) and can be alkylated at either the substituent or the ring nitrogen atom. 3-Methoxy groups are not replaced by nucleophiles, but both 3- and 5-alkylthio groups react readily, as does 3-methoxy-l,2-benzisothiazole. Alkylthio compounds can be oxidized to sulfoxides and sulfones, and the latter readily undergo nucleophilic replacement. All the hydroxy compounds react with phosphorus pentachloride to give the chloro derivatives. 

Benzisothiazole, 3-hydroxy-acylation, 6, 159 alkylation, 6, 159 chlorination, 6, 160 organophosphorus compounds, 6, 159... 

Activating groups at the 5-position led to high yields when bromination took place in chloroform or acetic acid. Products obtained were the 4-bromo derivatives of 5-amino- (90%), 5-hydroxy- (95%), and 5-methoxy-benzisothiazole (40%). Use of the bromine-sulfuric acid-silver sulfate system raised the yield of the last-named product to 87% [80JCR(S)197], 7-Amino-4-chloro-l,2-benzisothiazole was brominated in the 6-position [71JCS(C)3994],... 

Hartung and co-workers have reported that oxidation of isothiazolium salts such as 13 with H2O2 in AcOH led to stable 3-hydroperoxy-2-phenylhexahydro-l,2-benzisothiazole 1-oxides 14 which could be isolated in fair-to-good yields (38-70%). 3-Hydroperoxy and 3-hydroxy sultams were observed as over oxidation products in some cases and was dependent on the substituent present in the 2-aryl ring <99HCA685>. 

The introduction of substituents into the position 3 does not change the reaction course [165, 167-169], 4-Amino-7-nitrobenzisothiazole in the sulfuric-nitric mixture forms 5,7-dinitro derivative in low yield [170], 4-Chloro-7-nitro-l,2-benzisothiazole was obtained as a result of the nitration of 4-chloro-l,2-benzisothiazole [171,172], 5-Hydroxy-l,2-benzothiazole is nitrated to the position 4, and in case of 5-hydroxy-4,6-dibromo-l,2-benzisothiazole a substitutive nitration to form 5-hydroxy-6-bromo-4-nitro isomer occurs [173],... 

Similarly to 1,2-benzisoxazoles, 1,2-benzisothiazoles with the nitro group in the arylene fragment can be obtained from 4-mercaptotocumarines and from hydroxy-lamine [167],... 

New mechanistic studies clarify the pathway from 4-hydroxy-2-methyl-27/-l,2-benzothiazine-3-substituted A.A-dioxide to 2-methyl-l,2-benzisothiazol-3-(277)-one 3, 3 -dioxide <1999H(51)131>. 

Hydroxyisothiazole exists as the hydroxy tautomer in nonpolar solvents, but more polar solvents result in a greater contribution of the 3-keto tautomer. Spectroscopic studies indicate that at least some 5-hydroxy isothiazoles exists in the 5-keto form. l,2-Benzisothiazol-3-one, 2,1-benzisothiazol-... 

The 3- and 5-hydroxy isothiazoles and the corresponding thiol compounds are either O- and S-or V-alkylated. Hydroxy compounds are readily converted to chloro derivatives. 3-Methoxy groups are reported not to be displaced by nucleophiles <84CHEC-I(6)l3l>, yet both alkoxy groups in a 3,4-diethoxy isothiazole can be displaced (see Section 3.05.7.5). 3-Methoxy-1,2-benzisothiazole and the 3- and 5-alkylthio groups in isothiazoles undergo displacement reactions. New reactions at the carbonyl group of saccharin derivatives have been reported (see Section 3.05.7.5). 

The benzo-l,3-azol-2-ones exist in the carbonyl tautomeric forms, lndazol-3-one, however, at least in dimethylsulfoxide solution, is largely in the hydroxy tautomeric form, in contrast to 1,2-benzisothiazol-3-one, which is wholly in the carbonyl form, in the solid. ... 

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