Isothiazolium salts

Benzisothiazole is also stable to hot alkali (72Ahc(14)43), in marked contrast to 2,1-benzisoxazole, but isothiazolium salts are dequaternized (77IJC(B)886). 1,2-Benzisothiazole... 

Isothiazolium salts (59) react with phenylhydrazine to give pyrazoles (60) (72AHC(14)l) (see Section 4.02.1.6). When treated with hydrazine hydrate, 3-chloro-l,2-benzisothiazole gives di-(o-cyanophenyl) disulfide (73SST(2)556), but 2,1-benzisothiazole gives o-aminobenz-aldehyde azine (72AHC( 14)43). 2-Substituted saccharins give the expected o-sulfamoyl-benzohydrazides. 

Alkyl-3-chloroisothiazolium chlorides (131) react with ammonia to give 3-alkyl-aminoisothiazoles (132) (80MI41700), but with amines give mixtures of isomeric isothiazolium salts (133 and 134 Scheme 20) (79JOC1118), compound (134) presumably being formed by a similar mechanism to compound (132). 2-Alkyl-3-chloro-l,2-benzisothiazolium salts... 

The first synthesis of stable 3-hydroperoxy-sultams (24) which are a new class of sultam with oxidising properties, was reported. The synthesis involved oxidation of the isothiazolium salts (23) with hydrogen peroxide in acetic acid. Reduction of (24) with aqueous sodium bisulphite afforded the corresponding novel 3-hydroxysultams whereas thermolysis in ethanol resulted in the elimination of water to give 3-ketone derivatives, which are versatile as dieneophiles <96T783>. 

Base-induced dimerization of isothiazolium salts containing an active methyl group in the 5-position provides a flexible approach for the synthesis of novel substituted 6aA4-thia-l,6-diazapentalenes. For example, salts 198 and 199 upon treatment with dicyclohexylamine in DMSO yielded the thiadiazapentalenes 200 as shown in Equation (51) and Table 27 <1996MOL142>. 

Table 27 Base-induced dimerization of isothiazolium salts 198 and 199 (Equation 51)...

Accordingly, iV-phenyl-substituted isothiazolium salts bearing a benzo crown ether substituent were employed in this synthetic protocol and led to the synthesis of various crown ether-substituted 6aA4-thia-l,6-diazapentalenes 201... 

The synthesis of novel substituted 6aA4-thia-l,6-diazapentalenes 33 was achieved by a base-induced dimerization of two isothiazolium salts <2001PS(170)29>. It was shown that A -phenyl-substituted isothiazolium salts having active 5-methyl or 5-methylene groups can easily be obtained by reaction of (l-thiocyanatovinylaldehydes and substituted anilines <1995CZ175>. 

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>. 

From Isothiazolium Salts and Other Reactions. An interesting synthesis of benzo-TA is based on recyclization of chlorothiazolium salts 93 by the action of formamides. The quantitative yield of products depends on the formamide used and the reaction conditions. If R is a sterically encumbered group (Me2CH, Me3C, or Ph), benzo-TAs 94 are formed, while other formamides give isomers 95. With 1,2-dichlorobenzene, only the isomers 94 were obtained. The regioselectivity of this reaction was explained by the position of nucleophilic attack of the formamide (71CB3757) (Scheme 30). 

Isothiazolium salts have been reconverted to isothiazoles by dry distillation27 and by treatment with ammonia.145 The latter reaction incidentally confirms that isothiazoles are alkylated on the nitrogen and not the sulfur. Isothiazolium salts with a vacant 3-position have given 3-thiones on treatment with sulfur in pyridine [Eq. (16)].63,64... 

Bicyclic 5-5 Systems Three Heteroatoms 1 2 Table 12 Thieno[3,2-c]isothiazolium salts. 

Isothiazolium salts 226, which are prepared from P-thiocyanatovinyl aldehydes and anilines, can be oxidized with magnesium monoperoxyphthalate (MMPP) in water or alcohols to give 2-aryl-3-hydroxy-sultames 227 <03S2265>. This publication also reviews, in its introduction, a variety of other methods to form highly oxidized isothiazoles and their biological properties. 

The high-performance liquid chromatography (HPLC)-MS(MS) technique has been used for monitoring the oxidation of isothiazolium salts with H202/acetic acid <2003CHR147>. 

The base-catalyzed conversion of 5-alkyl-substituted isothiazolium salts 88 (R = Me, R = Et) to 2,3-dihydrothio-phene derivatives 329 occurs in basic conditions via intermediates 328. The distribution of diastereomers 329 is dependent on the base and aryl substituent <1997SUL35>. Similar behavior was observed in the case of 88 (R = R =-(0112)4-) <1996JPG424>. The condensation of 5-Me-substituted isothiazolium salts 88 with a second molecule of a different isothiazolium salts affords haA -thia-Eh-diazapentalenes 330. In this way, macrocyclic ethers 332 were prepared from 331 and their complexation behavior toward sodium(l), silver(l), and mercury(n) studied <2001PS(170)29>. 

Reaction of some isothiazolium salts (9) with hydrogen sulfide leads to unstable compounds which have been described as bis(l, 2-dithiol-3-yl) sulfides (10). These compounds are converted into 1,2-dithiolium salts (11) by strong acids such as hydrogen chloride or iodide, or perchloric acid. ... 

---