Alkylation benzothiazole derivatives

In the middle of the 1950s, Knott reported the synthesis of dyesmffs based on benzothiazole derivatives. Alkylation of Al-methylbenzo-l,3-thiazole-2-thione with a-bromoacetophenone and deprotonation of the resulting thiocarbonylium salt 5 yielded, after spontaneous desulfurization of the intermediate thiirane (7), the alkylidene derivative 8 (18) (Scheme 5.1). In order to rationalize the reaction, thiocarbonyl ylide 6 was proposed as the precursor of thiirane 7. To the best of our... 

Hydroxyl-substituted naphthimidazoles, benzothiazoles, benzimidazoles, benzotriazoles, benzoselenazoles and benzoxathiolones may be regarded as substituted phenolic couplers. Compound (121) is a specific example of the latter type which yields intense brown images (51USP2547843). In the absence of hydroxyl groups, alkyl-substituted derivatives of imidazoles or thiazoles may be couplers in their own right by virtue of their active alkyl substituent. 

Alkyl-A2-l,2,3,4-thiatriazolines 52 decompose on heating above 90 °C to form benzothiazole derivatives 53 <1971AP687, 1977JOC1159>. The (2 -cyanomethyl) derivative 10 (R = CH2CN) decomposes at 90°C to the 2-(methylamino)benzothiazole derivative 52 rather than to the fused 1,2,4-thiadiazolimine 54 that would have been expected as the result from an intramolecular masked 1,3-dipolar (see Section 6.09.6.2) cycloaddition (Scheme 11) <1992J(P1)181>. 

The thermal decomposition of 5-(dialkylamino)-3-alkylimino-l,2,4-dithiazoles (48) gives products derived from 2 molecules of the reactant, with loss of one atom of sulphur. They are formulated as the substituted 3,5-bis(thioureido)-l,2,4-thiadiazolidines (49) and are thought to arise by a mechanism involving intermediate spiranes. The 3-phenylimino-analogues of (48) decompose differently, yielding benzothiazole derivatives. The same class of 1,2,4-thiadiazolines (49) arise also by the successive alkylation and aminolysis of the 1,2,4-dithiazoles (50). ... 

The mesomeric effect of the C=S linkage is very pronounced and is responsible for the facile quaternization of heterocyclic N-alkylated thiones (159) this effect is operative even when such a shift does not increase the aromaticity of the ring. Thione derivatives of pyridazine, benzothiazole, quinazoline, 1,3-thiazine, triazole,and isoindole are examples of compounds which readily form quaternary salts. 

The reaction of dimedone with 3-alkyl-5-ercapto-1,2,4-triazoles 315 in the presence of NBS gives intermediates, which after reaction with a solution of aqueous sodium carbonate afford 2-alkyl-5a-hydroxy-6,6-dimethyl-8-oxo-5a, 6,7,8,8a-hexahydro[l,2,4]triazolo[3,2-3]benzothiazoles 49. Finally, reaction with PPA provides the dehydrated heterocyclic derivatives 316 (Scheme 30) <1999IJH127>. 

Af-(2,3-Dihydroimidazo[2,l-6]benzothiazol-6-, 7- and 8-yl)aminomethy-lenemalonates (1474, R2 = H) were alkylated with dialkyl sulfate or alkyl halide in hexamethylphosphortriamide in the presence of sodium hydride to give N-alkyl-N-(2,3-dihydroimidazo[2, l-fe]benzothiazolyl)aminomethy-lenemalonates (1474, R2 = H). The hydrolysis of1474 by heating in boiling dilute hydrochloric acid for 15 min gave alkylamino derivatives (1475) (81EUP21806). 

Reaction of chloromethyl derivatives of 4 -aminophenyl-2-benzothiazoles with, e.g., A. A OY"-pcrmcthy 1 dicthy 1 cnetriamine leads to compounds with alkyl-amino alkylammonium residues that can be diazotized and coupled with, e.g., acetoacetarylides [129], Dye 42 is an example that colors paper in a greenish shade of yellow. 

Benzothiazoles are formed by the action of sulfur on alkyl- and acyl-anilines. The reaction is realized at elevated temperatures and is accompanied by secondary reactions. In certain cases (aryl and aroyl derivatives) the yields are satisfactory. Thus benzanilide (559) reacts with sulfur affording 2-phenylbenzothiazoIe (560) with a yield of 70%. Benzothiazole is obtained in a similar way (yield 21%) by the action of sulfur on (V,(V-dimethylaniline. 

Difluorobenzonitrile and methylthioglycolate cyclize to give 4-fluorobenzo[fe]thiophene [91JFC(54)104]. The reaction of trifluoromethyl-substituted 2,4-dinitrochloro- and 2,6-dinitrochlorobenzene with alkyl thi-oglycolates and amino acid esters at room temperature in the presence of triethylamine follows the same mechanistic concept to yield trifluoromethyl-substituted benzothiazole and benzimidazole derivatives [88JFC(38)327] (Scheme 25). 

Baudin, J. B., Hareau, G., Julia, S. A., Ruel, O. A direct synthesis of olefins by the reaction of carbonyl compounds with lithio derivatives of 2-[alkyl- or 2 -alkenyl- or benzylsulfonyl]benzothiazoles. Tetrahedron Lett. 1991, 32,1175-1178. 

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