Benzothiazole precursor

Synthesis of the title compounds from benzothiazole precursors has also been accomplished by cyclocondensation of 2-chlorobenzothiazole (282) with anthranilic acids or their esters (34JIC463 53JA712, 53JOC1380 75JIC886 79CB3424, 79PHA138). 

In its UV-Vis spectmm, 51 showed a bathochromic shift band (362 nm) with respect to the precursor (351 nm). This is due to the effect of the amino substituent in the benzothiazole precursor. A single fluorescence emission band was observed in 51 at 500 nm, while the precursor showed a maximum located at 499 nm. A Stokes shift (AA) of 138 and 148 nm could be detected for 51 and the precursor, respectively. Small blue-shifted bands at 386 and 373 nm could be observed for 51 and the precursor, respectively, with Stokes shift (AA) of 121 and 135, respectively <2004TL5601>. 

Some modifications of the procedures B and C have been reported for the preparation of 5-(benzothiazol-2-yl)- or 5-acetyl derivatives 22 (88AP509) and 23 [87ZN(B)107], The use of the sulfur precursor 24 (85S432) or nonsulfur starting components 26 [87ZN(B) 107] led to biheter-ocyclic 4//-thiopyrans 25 or 27, respectively. 

Thiazolonaphthyridinium salts 331 can be produced either by bromination of the 2-alkenylpyridine precursor, or by thermal cyclization of the 2-(bromoacetyl)pyridine (Scheme 81) <1997CL1203>, and reaction of the pyrano-pyrimidine 332 with o-aminothiophenol gives the benzothiazole-fused pyridopyrimidinedione 333 (Equation 118) <2003JCCS887>. 

Trying to prepare precursors for the synthesis of 3-substituted [l,2,4]triazolo[5,l- ]benzothiazoles, 2-hydrazino-4-methylbenzothiazole 393 was submitted to reaction with formic acid, urea, carbon disulfide, and acetic anhydride to give compounds 230, 238, 89, and 394 (Scheme 45) <1998IJC(B)921>. 

In the case of the benzothiazole system, both aldehydes and mixed ketones have been synthesized by reduction or alkylation of the appropriate carbonyl precursors. The carbonyl compounds are in turn prepared from the benzothiazole-2-anion either directly by reaction with esters or indirectly by reaction with aldehydes followed by PCC oxidation (Scheme 154) (85H2467 91BCJ3256). 

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... 

Di Nunno, L. Franchini, C. Scilimati, A. Sinicropi, M. S. Tortorella, P. Chemical and hemoenzymatic routes to l-(benzothiazol-2-yl-sulfanyl)-3-chloropropan-2-ol, a precursor of drugs with potential /-blocker activity. Tetrahedron Asymmetry 2000, 11, 1571-1583. Cavelier, F. First synthesis of the enantiomerically pure a-hydroxy analogue of S-tert-butyl cysteine. Tetrahedron Asymmetry 1997, 8, 41-43. 

The four (pyrano[2,3- ]benzothiazol-2-yl)benzamides (72) shown in Equation (39) were obtained in good yield by heating 6-aminoflavone-derived thiourea precursors in POCl3 containing PC15 <94BCJ2326>. 

Benzotriazole-mediated reactions feature in synthetic routes to the isoindolo- and pyrrolo-fused benzothiazole derivatives 272 (e.g. R1 = CH3, R2 = R3 = H) and 273 (e.g. R1 = R3 = H, R2 = Cl) in good overall yields the common precursors were the thioamines 271... 

Nitrobenzothiazole chromophores [588, 589] and their precursors [590] are building blocks of nonlinear optical materials, which are extensively used in the field of optical information processing, optical sensing, data storage, and telecommunications [588, 591], 5-Nitro- [590] and 6-nitro-2-(methyamino)benzothiazole [589] have been prepared from 3-nitro- and 4-nitrophenylthiourea correspondingly, as illustrated in Scheme 2.105. 

UV-Vis absorption and fluorescence emission of Troger base analogue 51 and its precursor 2-(4-amino-2-hydro-xyphenyl)benzothiazole were measured. In the UV-Vis spectra, all molar extinction coefficient values were in the order of 104lmol 1 cm as expected for 71-71 transitions. 

Note Using lithiated thiazoles or benzothiazoles can result in low yields of the carbene complex precursor due to an equilibrium between the cyclic and acyclic forms [59] (see Figure 6.19). 

An alternative route to benzyne from 107 might involve formation and decomposition of 1,2,3-benzthiadiazole-l-oxide 114. However, independent synthesis of 114 showed that it is remarkably stable its thermal decomposition requires a temperature of 135 C Consequently 114 cannot be an intermediate in the room-temperature diazotizations. This is in sharp contrast with 1,2,3-benzothiazole-1,1-dioxide 115, which is a well-known benzyne precursor at 0 °C and which explodes spontaneously in the solid state. It is a plausible intermediate in the diazotization of 116, which affords biphenylene and dibenzo-... 

The most important strategy for the synthesis of benzothiazoles, benzimidazoles, and benzoxazoles is the insertion of C-2 into a precursor with ortho heteroatoms on a benzene ring. The component which is required for this purpose usually has the future C-2 at the oxidation level of an acid, but many variants on this have been described. 

Ma recently demonstrated that 2-haloanilides can undergo coupling with metal sulfides subsequent intramolecular condensation affords substituted benzothia-zoles (3). Thioamides and thioureas also serve as precursors to benzothiazoles (vide infra). In addition to S -arylation reactions, alkenyl halides are also effective... 

Hattori T, Akita H, Kakimoto M and Imai Y (1992) Novel 2-step synthesis of poly(benzothiazoles) via new precursor polyamides from 2,5-bis [(methoxycarbonyl)ethyl]thio -l,4-phenylenediamine and aromatic dicarboxylic-acid chlorides. Macromolecules 25 3351-3355. 

R., Ashraf, C.M. and Rogers, R.D., Solvent-free synthesis of benzothiazole-based quaternary ammonium salts Precursors to ionic liquids, Arkivoc, 19-37 (2010). 

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