1.2.5- Thiadiazoles 1.2- benzisothiazoles

Fig. 1. HeterocycHc amines usedia azo dyes, (a) 2-Amino-6-nitrohenzothiazo1e [6285-57-0], (b) 3-amiao-5-nitro-2,l-benzisothiazole [14346-19-1], (c) 3-amiQo-4JT-l,2,4-triazole [65312-61 -0], (d) 5-amiQo-l,2,4-thiadiazole [7552-07-0, (e) 4,4 -diamiQo-2,2 -biphenylsulfone [6259-19-4], (f)...

In contrast to thiazoles, certain isothiazoles and benzisothiazoles have been directly oxidized to sulfoxides and sulfones. 4,5-Diphenyl-l,2,3-thiadiazole is converted by peracid into the trioxide (146). Although 1,2,5-thiadiazole 1,1-dioxides are known, they cannot be prepared in good yield by direct oxidation, which usually gives sulfate ion analogous to the results obtained with 1,2,4- and 1,3,4-thiadiazoles (68AHC 9)107). 

There are many related examples which are now known as the general Dimroth rearrangement. For example, 3-ethylamino-l,2-benzisothiazole (419) is in equilibrium in aqueous solution with the 2-ethyl-3-imino isomer (420) <72AHCf 14)43). Dimroth rearrangements are known in the 1,2,4-thiadiazole series (421- 422), and in the 1,3,4-thiadiazole series as products of reactions of halogeno-l,3,4-thiadiazoles see Section 4.02.3.9.1 <68AHC(9)165). For a similar example in the 1,2,3,4-thiatriazole series, see Section 4.02.3.1.9. 

Although 1,2,5-thiadiazoles have been shown to undergo cycloaddition with benzyne <82CC299>, the predominant mode of attack is at sulfur. The result is extrusion of a nitrile and formation of a 1,2-benzisothiazole (22) (Scheme 4) <88JCS(Pl)2l4l>. 

The largest proportion of the dyes of this type, which can range from yellow to blue in colour, is of the homocyclic type. Examples such as those derived from 5-amino-l,2,4-thiadiazoles (32), 2-aminobenzothiazoles and 3-amino-2,l-benzisothiazoles (74MI11201) are in the minority. Synthesis is usually via diazotization of the appropriate heteroaromatic amino group and coupling with quaternary aniline derivatives. 

To produce disperse dyes having the brightness of the anthraquinone system and the color strength of the azo system, azo dyes based on heteroaromatic amines were developed.26-28 Examples are C.I. Disperse Red 145, Disperse Blue 148, Disperse Red 156, and C.I. Disperse Blue 339. These dyes employ aminated thiazoles, benzothiazoles, benzisothiazoles, and thiadiazoles in their... 

Okazaki and co-workers have recently obtained spectroscopic evidence at low temperatures (< 90K) for the existence of the di-t-butyl derivative (124) obtained photolytically from the corresponding 2,1-benzisothiazole (89CL2083 92JA1830). The absorption at 470 nm assigned to species 124 is in agreement with previous data obtained by Pedersen et al. during the photolysis of benzo[c]l,2,5-thiadiazole-2-oxide (125) at 20K, which was considered to produce the thionitroso species 127 [78ACS(B)625]. 

X = S) to DMAD to yield dimethyl 5-phenylisothiazole-3,4-dicarboxylate is much slower than the corresponding oxathiazolone (282) (X = O) <89JCS(Pl)2489>. The thermal decomposition of ethyl 2-azido-3-(3-azido-2-thienyl)propenoate (283) results in the formation of ethyl 5-cyano-isothiazole-3-carboxylate (284) together with the thienopyridazine (285) <84JCS(P1)915>. The addition of benzyne to 3,4-dimethyl-1,2,5-thiadiazole (286) gives 3-methyl-1,2-benzisothiazole <82CC299>. 

A slurry of benzenediazonium 2-carboxylate (from anthranilic acid and pentyl nitrite) in THF added in portions during 30 min to startg. 1,2,5-thiadiazole in the same solvent under reflux, and heating continued for 30min - 5-(l,2-benzisothiazol-3-yl)pentanonitrile. Y 53% (based on recovered thiadiazole). F.e. inch 3-chloro- and 3-alkoxy-derivs., also Se-analogs, s. M.R. Bryce et al., J. Chem. Soc. Perkin Trans. I 1988, 2141-4. 

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