2- Aryl benzothiazole

Important variants for the synthesis of benzimidazoles allow the use of aldehydes, rather than acids ytterbium triflate (best for aliphatic aldehydes) or scandium triflate catalyse the condensation and the subsequent air oxidation of the dihydrobenzimidazole immediate product. Incorporating nitrobenzene in the reaction mixture as the oxidant can also be used. orf/to-Nitroanilines can be used by incorporating a reducing agent in the reaction mixture - e.g. hydrogen over palladium or sodium dithionite - for in situ generation of the orffto-phenylenediamine. 2-Aryl-benzothiazoles can be made from 2-aminobenzenethiol, aromatic aldehydes and air, in the presence of activated carbon. ... 

Wang K, Guengerich FP (2012) Bioactivation of fluorinated 2-aryl-benzothiazole antitumor molecules by human cytochrome P450s 1A1 and 2W1 and deaetivation by cytochrome P450 2S1. Chem Res Toxicol 25 1740-1751... 

Direct Arylation of Heteroarenes, Aryl silicon reagents were employed to directly arylate heteroarenes via a Pd-catalyzed, ligand-free process. Silver(I) fluoride was the most effective source of fluoride (93%) compared with FeFs, KF, wBu4NF-H20, and CsF, although CuF2 gave a comparable performance (82%). In addition to activating the arylsilanes, silver(I) fluoride acts as a co-oxidant with Cu(0Ac)2-H20 to oxidize Pd° to Pd. The electron-rich and electron-deficient aryl (trimethoxy)silanes could be coupled to access arylated benzothiazoles in excellent yields (83-93%) (eq 19). 

Benzothiazole, 2-amino-6-thiocyanato-azo dyes from, 1, 328 Benzothiazole, 2-aryl-synthesis, 6, 321 Benzothiazole, 2-arylamino-synthesis, 6, 323 Benzothiazole, 2-aryloxy-Fries rearrangement, 6, 289 Benzothiazole, 2-benzyl-picrate, 6, 252 Benzothiazole, 2-chloro-dyes from, 1, 321-322 synthesis, 6, 323 Benzothiazole, 2,3-dihydro-oxidation, 6, 272 Benzothiazole, 2-dimethylamino-synthesis, 5, 128... 

Related reactions, that have been catalysed by NHC/Pd systems, are the intramolecular Mizoroki-Heck using catalysts formed in situ from imidazolium salts and a Pd(0) source [69], and the arylation of allylic alcohols by a benzothiazole-Pd complex [70,71] (Scheme 6.14). 

A number of Pd or Cu catalysts bearing NHC ligands have been prepared for carbonylation of aryl halides. Nacci and co-workers synthesised the benzothiazole carbene ligated Pd complex 32 (Fig. 9.6) and tested it for aryl halide carbonylation... 

In general, symmetrical oxo-squaraines having the same end-groups are synthesized by reacting squaric acid with two equivalents of quatemized indolenine, 2-methyl-substituted benzothiazole, benzoselenazole, pyridine, quinoline [39, 45, 46] (Fig. 4) in a mixture of 1-butanol - toluene or 1-butanol - benzene with azeotropic removal of water in presence [39, 45] or absence [47] of quinoline as a catalyst. Other reported solvent systems include 1-butanol - pyridine [48], 1-propanol - chlorobenzene, or a mixture of acetic acid with pyridine and acetic anhydride [49]. Low CH-acidic, heterocyclic compounds such as quatemized aryl-azoles and benzoxazole do not react, and the corresponding oxo-squaraines cannot be obtained using this method [23, 50]. 

Mercapto- benzothiazolates Dialkyl- dithiophosphates Dialkyl(aryl)- monothiophosphates Fatty carboxylates... 

A series of 2-arylbenzothiazoles 41 has been synthesized via microwave irradiation of 1 1 mixture of ortho-nm i noth iophenol s 39 and alkyl or aryl acylacetonitriles <06JHC1609>. This reaction appears to be more efficient than that of ort/20-aminothiophenols with (3-ketoesters to form substituted benzothiazoles reported previously <05H(65)2119>. 

A cobalt-catalyzed method for arylation of heteroarenes including thiazole and benzothiazole was reported in 2003 <030L3607>. According to this report, the direct C-5 arylation of thiazole with iodobenzene was carried out in the presence of cobalt catalyst [Co(OAc)2/IMes] and cesium carbonate, and a complete reversal of arylation from C-5 to C-2 was observed with the bimetallic Co/Cu/IMes system. This report has been retracted as the laboratory of the senior author has not been able to reproduce the key results disclosed in the communication <06OL2899>. 

The arylation of heteroaromatic compounds is also achieved by aryl-aryl coupling reaction. The arylation of A-methylimidazole with bromobenzene occurs under palladium catalysis (Equation (62)).72 The arylation of thiazole with aryl iodide occurs at the 2-position under PdCl2(PPh3)2/CuI catalysis.73 In this case, tetrabutylammonium fluoride improves the activity of the catalyst. Alternatively, thiazoles and benzothiazole are efficiently arylated... 

In addition to palladium catalysts, Co(OAc)2 shows a catalytic activity for the arylation of heterocycles, including thiazole, oxazole, imidazole, benzothiazole, benzoxazole, and benzimidazole.78 As shown in Scheme 6, the catalytic system Co(OAc)2/9/Cs2C03 gives G5 phenylated thiazole, while the bimetallic system Co(OAc)2/CuI/9/Cs2C03 furnishes the G2 phenylated thiazole. The rhodium-catalyzed reaction of heterocycles such as benzimidazoles, benzoxazole, dihydroquinazoline, and oxazoline provides the arylation product with the aid of [RhCl(coe)]2/PCy3 catalyst.79 The intermediacy of an isolable A-heterocyle carbene complex is proposed. 

Diazadienes have been used in organic synthesis for the preparation of various heterocyclic compounds. Alkylation of 1,3-diazadienes 207 and the benz-fused analog 210 at the nitrogen atom by aryl acyl bromides provided the iV-alkyl amidinium bromides 208 and 211, which underwent annulation to the 2,3-dihydro-imidazo[2,l-A]thiazole 209 and imidazo[2,l- ]benzothiazoles 212, respectively (Equations 92 and 93) <2001S741, 2002J(P1)741>. 

Compound 98 reacts with carbon disulfide in the presence of an alkali solution to give 3 -mercapto-l,2,4-triazolo[4, 5 l,5][l,2,4]triazolo[3,4-A]benzothiazole 247. Treatment of product 98 with urea at 200°C for 4h affords 3 -hydroxy-l,2,4-triazolo[4, 5 l,5]-l,2,4-triazolo[3,4-A benzothiazole 99 (Scheme 20). Finally, the addition of concentrated phosphoric acid in the presence of sodium nitrite to compound 98 produces 1,2,3,4-tetra-zolo[l, 5 l,5]-l,2,4-triazolo[3,4- ]benzothiazole 248, and refluxing substituted benzaldehydes in acetic acid provides an easy access to 3 -aryl-l,2,4-triazolo[4, 5 l,5]-l,2,4-triazolo[3,4-A benzothiazoles 249 (Scheme 20) (Table 50) <2005IJC(B)625>. 

The Suzuki coupling of aryl halides was also extended to tosylates recently. Benzothiazole 5-tosylate reacted with m-xylene-2-boronic acid (6.13.) to give the coupled product in 94% yield using palladium acetate and a stericly congested biphenyl based phosphine ligand as catalyst.17 Another class of less commonly utilised cross-coupling partners are methyltio derivatives. In the presence of a copper salt, which activates the carbon-sulphur bond, 2-methyltio-benzotiazol coupled readily with a series of arylboronic acids.18... 

In the alternate approach arylboronic acids were coupled with A-aryhhio-succinimides. In the process the aryl group of the boronic acid replaces the succinimide moiety in the coupling partner. In the example presented (6.85.) the 2-thiothiophene derivative was converted to 2-(4 -fluorophenylthio)-thiophene in 76% yield. The procedure was successfully extended to benzothiazoles too.115... 

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