2- Substituted benzothiazoles

Manganese(III)-promoted radical cyclization of arylthioformanilides and a-benzoylthio-formanilides is a recently described microwave-assisted example for the synthesis of 2-arylbenzothiazoles and 2-benzoylbenzothiazoles. In this study, manganese triacetate is introduced as a new reagent to replace potassium ferricyanide or bromide. The 2-substituted benzothiazoles are generated in 6 min at 110°C imder microwave irradiation (300 W) in a domestic oven with no real control of the temperature (reflux of acetic acid) (Scheme 15). Conventional heating (oil bath) of the reaction at 110 °C for 6 h gave similar yields [16]. 

Heating thiazole with phenylazotriphenylmethane at 75 °C for 24 hours affords 2-phenyl-5-triphenylmethyl thiazole (75 Scheme 43). The 1-adamantyl radical and other nucleophilic alkyl and acyl radicals react with 2-substituted benzothiazoles in a homolytic ipso substitution yielding the corresponding 2-alkyl or 2-acylbenzothiazole (Scheme 44) (77CC316). 

Carboxylic acids (511) and their chlorides, anhydrides, amides, esters and nitriles, condense with o-aminothiophenols (507) or their zinc salts, affording 2-substituted benzothiazoles (513), the only exception being acetic acid. The intermediate o -acylaminothioph-enols (512) could be isolated and readily cyclized. The activation of carboxylic acids in... 

Acylaminothiophenols (554) dehydrate on heating in an acidic medium affording 2-substituted benzothiazoles (555 Scheme 294). 2-Acylaminothiophenols (558) are prepared by acylation of 2-aminothiophenols (556) or by reduction of di(o -acylaminoben-zene) disulfides (557) by various reducing agents (Scheme 295). 

Pattabiraman et al. [54] synthesized the 2-substituted benzothiazoles (xxxiv) from inexpensive, commercially available reagent (2-benzthiazole acetonitrile) via a one-pot microwave assisted relay reaction. 

Mu et al. [59] reported the microwave assisted synthesis of 2-substituted benzothiazoles (xxxix) by the Mn(lll)-promoted cyclization of substimted thiofor-manilides. 

Mu XJ, Zou JP, Zeng RS et al (2005) Mn(III)-Promoted cyclization of substituted thioformanilides under microwave irradiation a new reagent for 2-substituted benzothiazoles. Tetrahedron Lett 46 4345 347... 

Recently, the synthesis of 2-substituted benzothiazoles has been reported via an intramolecular cyclization of arylthioamides 237 by using hypervalent iodine reagents (typically Dess-Martin periodinane, DMP) in CH2GI2 at ambient temperature. The reaction proceeds via a thiyl radical 238 in high yields (85-95%) to give benzothiazoles 239 and is also amenable to solid-phase synthesis (Scheme 95) <2006JOC8261>. 

Benzothiazole can be metallated by treatment with butyllithium the compound thus formed reacts with various electrophiles to furnish 2-substituted benzothiazoles, e.g. (282 equation 151). ... 

Alkyl-, aryl-, and hetaryl aldehydes react with o-aminothiophenol in DMSO to give the corresponding 2-substituted benzothiazoles (371) (Equation (76)) <90DP243>. Similar reactions with carboxylic acids <90MI 306-02), esters, and nitriles <92MI 306-03) have been described. 

Dimethyldithioallenes (380) are also capable of reacting with o-aminothiophenol affording 2-substituted benzothiazoles (381) (Scheme 94) <90CB54i). 

The synthesis of 2-substituted benzothiazoles has been also described by using o-aminothiophenol... 

An intramolecular aromatic nucleophilic substitution has been used for the preparation of 2-substituted benzothiazoles (388) in high yields from o-halothioanilides (387), the halogen atoms being iodine, bromide, or chlorine <82TL5093>. This reaction can also be carried out with naphtho-derivatives <89ijc(B)597>. Moreover, in the presence of sodium carbonate, the reaction can be extended to fluorine-substituted substrates (Equation (81)) <89JHC1039>. 

Phenylthioarylimines (391) cyclize to 2-substituted benzothiazoles (388) upon treatment with diisopropylperoxydicarbonate (DPDC). The formation of biphenyl alongside (388) has been con-... 

The reaction of (230) with a variety of electrophiles such as aldehydes, ketones, and esters, to give the corresponding 2-substituted benzothiazoles was more extensively examined later on (see Section 3.06.7.10.1) <868375, 85H(23)2509, 88803637). However, in most of the cases the cleavage of the benzothiazole ring to the formyl group was not carried out and therefore the actual synthetic equivalence of these products to substituted aldehydes remained unproved. In a few synthetic schemes, the benzothiazole-to-formyl equivalence has been completely exploited <90H(3l)2l25, 93JOC5931). 

N- Arylthioamides or thioanilides (518) which are usually prepared from the corresponding amides by sulfurization, are oxidized in basic medium by potassium ferricyanide to 2-substituted benzothiazoles (519 Scheme 281) (Jacobson s method). The best yields are obtained for arylamines bearing electron-donating groups which enhance the electron density ortho to the nitrogen atom. 

Substituted benzothiazoles 201 (R = NH2) were rearranged to thiazolo[5,4-c]azepin-8-one 615 under the conditions of Schmidt reaction. 

Synthesis. - From oviho-Aminobenzenethiols (Type A S-C 4 N + C). The cyclization between RNC and 0-NH2C6H4SH gives a 2-substituted benzothiazole. ... 

Additional examples of the DMP-mediated oxidations of nitrogen substrates include the synthesis of 2-substituted benzothiazoles 903 via oxidative cyclization of thioanilides 902 [445] and the synthesis of imldes (e.g., 904), N-acyl vinylogous carbamates and ureas and nitriles by the oxidation of amides and amines with DMP (Scheme 3.362) [1292],... 

New progress in the synthesis of 2-substituted benzothiazole derivatives 13CJ01423. 

Li, Y. Wang, Y Wang, J. A simple iodine-promoted synthesis of 2-substituted benzothiazoles by condensation of aldehydes with 2-aminothiophenol. Chem. Lett. 2006,35,460-461. 

Moghaddam, F. M. Ismaili, H. Bardajee, G. R. Zirconium (IV) oxide chloride and anhydrous copper (II) sulfate mediated synthesis of 2-substituted benzothiazoles. Hetemat. Chem. 2006,17, 136-141. 

More recently, a procedure for the synthesis of 2-substituted benzothiazoles via cyclization of o-iodothiobenzanilides was developed. The reaction uses inexpensive, readily available Pd/C as the catalyst without the addition of a ligand or additive, and works at room temperature in DMF. A variety of 2-aryl-, 2-allg l-, and 2-aminobenzothiazoles were prepared in good yields. However, the recycling of this Pd/C catalyst was not tested by the authors. In 2007, Itoh and Mase demonstrated the synthesis of benzothiazoles from 2-bromoanilides and thiol by using Pd2(dba)3/Xantphos as the... 

S. Chen, M. S. Hossain, F. W. Foss, ACS Sustainable Chem. Eng. 2013, 1, 1045-1051. Bioinspired oxidative aromatiza-tions one-pot syntheses of 2-substituted benzothiazoles and pyridines by aerobic organocatalysis. 

Cheng, Y., Peng, Q., Fan, W., and Li, P. (2014). Room-temperature ligand-free Pd/C-catalyzedC — S bond formation synthesis of 2-substituted benzothiazoles. 7. Org. Chem., 79, 5812-5819. 

Substituted benzothiazoles are formed in a Pd(0)-catalyzed cross-coupling sequence from 2-bromoanilides 14)and fS-mercaptopropionate 15 as SH-transfer reagent [366] ... 

H.-L. Jin, T.-X. Cheng, J.-X. Chen, Cerium-catalyzed tandem synthesis of 2-substituted benzothiazoles in PEG, Appl. Organomet. Chem. 25 (2011) 238-240. 

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