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Synthesis of benzothiazoles

Recent Literature

A three-component reaction of o-iodoanilines or electron-rich aromatic amines with K2S and DMSO provides 2-unsubstituted benzothiazoles in good isolated yields with good functional group tolerance. A similar reaction of o-phenylenediamines provided 2-unsubstituted benzimidazoles without K2S. DMSO plays three vital roles: carbon source, solvent, and oxidant.
X. Zhu, F. Zhang, D. Kuang, G. Deng, Y. Yang, J. Yu, Y. Liang, Org. Lett., 2020, 22, 3789-3793.

A simple, green, and efficient method enables the synthesis of benzoxazoles and benzothiazoles from o-amino(thio)phenols and aldehydes using samarium triflate as a reusable acid catalyst under mild reaction conditions in aqueous medium.
P. B. Gorepatil, Y. D. Mane, V. S. Ingle, Synlett, 2013, 24, 2241-2244.

Supramolecular nanoassemblies of an AIEE-ICT-active pyrazine derivative (TETPY) with strong absorption in the visible region catalyze the synthesis of a variety of a broad range of benzimidazoles, benzothiazoles and quinazolines in excellent yields under "metal-free" conditions in a mixed aqueous media.
S. Dadwal, M. Kumar, V. Bhalla, J. Org. Chem., 2020, 85, 13906-13919.

In a visible light mediated synthesis of benzothiazoles from 2-aminothiophenol and aldehydes, an in situ-generated disulfide photosensitizes molecular oxygen to generate the key oxidants, singlet oxygen and superoxide anion, for the dehydrogenation step.
H. S. Hwang, S. Lee, S. S. Han, Y. K. Moon, Y. You, E. J. Cho, J. Org. Chem., 2020, 85, 11835-11843.

Iodine promotes a condensation of 2-aminothiophenol with aldehydes in DMF, which efficiently provides 2-substituted benzothiazoles.
Y. Li, Y.-L. Wang, J.-Y. Wang, Chem. Lett., 2006, 460-461.

A straightforward synthesis of 2-arylbenzothiazoles from 2-aminothiophenol and aryl aldehydes in air/DMSO oxidant system is operationally simple, proceeds without catalysts, tolerates a wide range of functionalities, and provides desired products in good to excellent yields.
R. Hu, X. Li, Y. Tong, D. Miao, Q. Pan, Z. Jiang, H. Gan, S. Han, Synlett, 2016, 27, 1387-1390.

A simple microwave-accelerated condensation of 2-aminothiophenol and aromatic aldehydes in an inexpensive ionic liquid, 1-pentyl-3-methylimidazolium bromide ([pmIm]Br) provides 2-arylbenzothiazoles under solvent and catalyst-free condition. The ionic liquid can be recycled for subsequent reactions.
B. C. Ranu, R. Jana, S. S. Dey, Chem. Lett., 2004, 286-287.

Iodine catalyzes simple and practical syntheses of 2-aroylbenzothiazoles and 2-arylbenzothiazoles from 2-aminobenzenethiols and acetophenones under metal-free conditions. Reactions in DMSO as oxidant and reaction medium provide 2-aroylbenzothiazoles, whereas the use of nitrobenzene as oxidant in dioxane as solvent enables the synthesis of 2-arylbenzothiazoles.
R. Ma, Y. Ding, R. Chen, Z. Wang, L. Wang, Y. Ma, J. Org. Chem., 2021, 86, 310-321.

Efficient reactions of α-keto acids with 2-aminobenzamides, 2-aminobenzenethiols, benzene-1,2-diamines, and 2-aminophenols provide quinazolinones, benzothiazoles, quinoxalinones, and benzoxazinones under catalyst-free conditions, using water as the solvent. Products can be easily purified through filtration and washing with ethanol (or crystallized).
J. Huang, W. Chen, J. Liang, Q. Yan, Y. Fan, M.-W. Chen, Y. Peng, J. Org. Chem., 2021, 86, 14866-14882.

Reactions of ortho-substituted anilines and arylglyoxylic acids in DMSO at 40°C provide various benzo-fused five- to six-membered N-heterocycles in very good yields. The reaction proceeds via intramolecular Michael addition of α-iminocarboxylic acids, generated in situ, with an ortho-substituted nucleophile, followed by decarboxylation forms the N-heterocycles.
J. K. Laha, M. K. Hunjan, J. Org. Chem., 2022, 87, 2315-2323.

A copper-catalyzed condensation of 2-aminobenzenethiols with nitriles enables an efficient and convenient synthesis of 2-substituted benzothiazoles. The developed method is applicable to a wide range of nitriles containing different functional groups furnishing excellent yields of the corresponding products.
Y. Sun, H. Jiang, W. Wu, W. Zeng, X. Wu, Org. Lett., 2013, 15, 1598-1601.

The use of elemental sulfur as traceless oxidizing agent enables a remarkably simple solvent-free and catalyst-free synthesis of benzazoles from alkylamines and o-hydroxy/amino/mercaptan anilines.
T. B. Nguyen, L. Ermolenko, W. A. Dean, A. Al-Mourabit, Org. Lett., 2012, 14, 5948-5951.

Inexpensive and reusable graphitic carbon nitride (g-C3N4) catalyzes a metal-free synthesis of benzothiazoles via intramolecular C-H functionalization/C-S bond formation under visible-light irradiation. This reaction provides 2-substituted benzothiazoles in high yields under an air atmosphere at room temperature without addition of a strong base or organic oxidizing reagents.
J. Bai, S. Yan, Z. Zhang, Z. Guo, C.-Y. Zhou, Org. Lett., 2021, 23, 4843-4848.

KOtBu promotes a mild intramolecular C-S cross-coupling of ortho-iodothioanilides in the presence of a catalytic amount of phenanthroline as an additive for the convenient synthesis of a wide variety of 2-alkyl- and 2-aryl-substituted benzothiazoles in excellent yields.
A. Nandy, G. Sekar, J. Org. Chem., 2021, 86, 15825-15834.

Visible light mediates facile syntheses of isoquinolines, benzothiazoles, and quinazolines from isocyanides and inexpensive acyl peroxides. Singlet-excited isocyanides decompose acyl peroxides into aryl/alkyl radicals. The latter attack the isocyanides, yielding imidoyl radicals that subsequently cyclize to afford heteroarene products.
N. Yadav, S. R. Bhatta, J. N. Moorthy, J. Org. Chem., 2023, 88, 5431-5439.

Triggered by alkyl radicals, varieties of 2-isocyanoaryl thioethers containing aliphatic, aryl, and heteroaromatic groups can be cleaved and precisely reinstalled to give benzothiazole derivatives. Mechanistic studies reveal that the cascade reaction undertakes an intermolecular pathway.
K. Luo, W.-C. Yang, K. Wei, Y. Liu, J.-K. Wang, L. Wu, Org. Lett., 2019, 21, 7851-7856.

An ionic cascade insertion/cyclization reaction of thia-/selena-functionalized arylisocyanides enables an efficient and practical synthesis of 2-halobenzothiazole/benzoselenazole derivatives. Additionally, a facile access to 2-aminobenzothiazoles is also achieved by the one-pot cascade reaction of 2-isocyanoaryl thioethers, iodine, and amines.
J. Dong, J. Hu, X. Liu, S. Sun, L. Bao, M. Jia, X. Xu, J. Org. Chem., 2022, 87, 2845-2852.

A highly efficient reaction of readily available aromatic amines, benzaldehydes, and NH4SCN as a sulfur source provides 2-arylbenzothiazoles with wide functional group compatibility in good yields via an iodine-mediated oxidative annulation.
A. Dey, A. Hajra, Org. Lett., 2019, 21, 1686-1689.

A copper-promoted [3 + 1 + 1]-type cyclization reaction enables a selective construction of 2-aryl or 2-benzyl substituted benzothiazoles from o-iodoaniline derivatives, S8, and N-tosylhydrazones depending on the reaction system.
Y. Huang, P. Zhou, W. Wu, H. Jiang, J. Org. Chem., 2018, 83, 2460-2466.

A selective, TBHP/KI-promoted C-O bond cleavage of ethers followed by annulation with anilines and elemental sulfur provides a wide range of 2-aryl-, 2-heteroaryl-, and 2-alkyl-substituted benzothiazoles with satisfactory yields and good functional group compatibility under transition-metal-free conditions.
J. Zhang, X. Zhao, P. Liu, P. Sun, J. Org. Chem., 2019, 84, 12596-12605.

A three-component reaction of nitroarenes, alcohols, and sulfur powder provided 2-substituted benzothiazoles in good yield with a good functional group tolerance via nitro reduction, C-N condensation, and C-S bond formation.
Q. Xing, Y. Ma, H. Xie, F. Xiao, F. Zhang, G.-J. Deng, J. Org. Chem., 2019, 84, 1238-1246.

A decarboxylative redox cyclization strategy enables the synthesis of 2-substituted benzothiazoles from o-chloronitroarenes and arylacetic acids in the presence of elemental sulfur/N-methylmorpholine under metal- and solvent-free conditions.
T. Guntreddi, R. Vanjari, K. N. Singh, Org. Lett., 2015, 17, 976-978.

A synthesis of 2-substituted benzothiazoles in good yields from o-iodoanilines, arylacetic acids, and elemental sulfur is catalyzed by cheap copper metal. This S8-mediated directed decarboxylative redox-cyclization strategy is operationally simple, ligand-free, and compatible with a wide range of functional groups.
X. Wang, X. Li, R. Hu, Z. Yang, R. Gu, S. Ding, P. Li, S. Han, Synlett, 2018, 29, 219-224.

A photocatalyst- and transition-metal-free visible-light-induced dehalogenative cyclization of ortho-halothiobenzanilides provides 2-aryl benzothiazoles with high efficiency and selectivity. This photocyclization tolerates various functional groups and is applicable for the synthesis of 2-alkyl benzothiazoles.
H. Wang, Q. Wu, J.-D. Zhang, H.-Y. Li, H.-X. Li, Org. Lett., 2021, 23, 2078-2083.

A visible-light-driven, intramolecular C(sp2)-H thiolation without addition of a photosensitizer, metal catalyst, or base induces the cyclization of thiobenzanilides to benzothiazoles. The substrate undergoes a reverse hydrogen-atom transfer (RHAT) in its excited state with TEMPO to form a sulfur radical, which adds to the benzene ring followed by a rearomatization via RHAT.
Z.-M. Xu, H.-X. Li, D. J. Young, D.-L. Zhu, H.-Y. Li, J.-P. Lang, Org. Lett., 2019, 21, 237-241.

Visible light mediates a transition-metal-free formation of benzothiazoles from thiobenzanilides in the presence of riboflavin as a photosensitizer and potassium peroxydisulfate as a sacrificial oxidizing agent. This methodology tolerates a broad range of functional groups and affords 2-substituted benzothiazoles in good yields under very mild conditions.
L. M. Bouchet, A. A. Heredia, J. E. Argüello, L. C. Schmidt, Org. Lett., 2020, 22, 610-614.

An external oxidant-free oxidative coupling for aromatic C-H thiolation using visible-light photoredox cobalt-catalysis affords benzothiazoles in good to excellent yields with only H2 as a side product. When catalytic TBAOH was used as the base, not only 2-aryl but also 2-alkylbenzothiazoles could be obtained.
G. Zhang, C. Liu, H. Yi, Q. Meng, C. Bian, H. Chen, J.-X. Jian, L.-Z. Wu, A. Lei, J. Am. Chem. Soc., 2015, 137, 9273-9280.

Copper-catalyzed double C-S bond formation enables a highly efficient synthesis of benzothiazoles from easily available N-benzyl-2-iodoanilines and potassium sulfide via a traditional cross-coupling and an oxidative cross-coupling reaction.
X. Zhang, W. Zeng, Y. Yang, H. Huang, Y. Liang, Org. Lett., 2014, 16, 876-879.

The use of K2S2O8 enables a nontransition metal-catalyzed synthesis of 2-aryl benzothiazoles through oxidative condensation of benzothiazoles with aryl aldehydes or phenylglyoxylic acids.
Z. Yang, X. Chen, S. Wang, J. Liu, K. Xie, A. Wang, Z. Tan, J. Org. Chem., 2012, 77, 7086-7091.

Brønsted acid catalyzed cyclization reactions of 2-amino thiophenols and anilines with β-diketones under oxidant- and metal-free conditions give 2-substituted benzothiazoles and benzimidazoles in good yields, respectively. Various groups such as methyl, chloro, nitro, and methoxy linked on benzene rings were tolerated under the optimized reaction conditions.
M. S. Mayo, X. Yu, X. Zhou, X. Feng, Y. Yamamoto, M. Bao, Org. Lett., 2014, 16, 764-767.

The reaction of ortho-substituted anilines with functionalized orthoesters yields benzoxazole, benzothiazole, and benzimidazole derivatives in an efficient and connective methodology. The versatility of this approach enables the development of new libraries of heterocycles containing multifunctional sites.
G. Bastug, C. Eviolitte, I. E. Markó, Org. Lett., 2012, 14, 3502-3505.

Various 2-bromoanilides were reacted with 2-ethylhexyl 3-mercaptopropionate in high yields using a palladium catalyst. Subsequent generation of thiols and condensation under basic or acidic conditions allows a convenient synthesis of substituted benzothiazoles.
T. Itoh, T. Mase, Org. Lett., 2007, 9, 3687-3689.

A convenient method for the synthesis of 2-substituted benzimidazoles and benzothizoles offers short reaction times, large-scale synthesis, easy and quick isolation of the products, excellent chemoselectivity, and excellent yields as main advantages.
K. Bahrami, M. M. Khodaei, F. Naali, J. Org. Chem., 2008, 73, 6835-6837.

A one-pot tandem reaction of benzyl halides and o-aminobenzenethiol gives benzothiazoles in high chemical yields under mild conditions in DMSO in the absence of an additional oxidant. Both benzyl chlorides and bromides bearing a range of substituents proved to be suitable substrates.
C. Zhu, T. Akiyama, Synlett, 2010, 2345-2351.

An aerobic visible-light driven photoredox catalytic formation of 2-substituted benzothiazoles through radical cyclization of thioanilides features C-H functionalization and C-S bond formation with no direct metal involvement except the sensitizer. In this reaction, visible-light is the driving force, molecular oxygen the terminal oxidant, and water the only byproduct.
Y. Cheng, J. Yang, Y. Qu, P. Li, Org. Lett., 2012, 14, 98-101.

Dess-Martin periodinane (DMP) efficiently mediates the intramolecular cyclization of phenolic azomethines at ambient temperature leading to substituted benzoxazoles and benzothiazoles. Treatment of the reaction mixtures sequentially with Amberlyst A-26 thiosulfate resin and diisopropylaminomethyl resin (PS-DIEA) removes excess reagent and byproducts, to give pure products.
D. S. Bose, M. Idrees, Synthesis, 2010, 398-402.

Various benzothiazoles were synthesized by the intramolecular cyclization of thioformanilides using 2,6-dichloro-3,5-dicyano-1,4-benzoquinone (DDQ) in dichloromethane at ambient temperature in high yields.
D. S. Bose, M. Idrees, B. Srikanth, Synthesis, 2007, 819-823.

The use of Pd/C as catalyst enables a ligand-free and additive-free synthesis of 2-substituted benzothiazoles via cyclization of o-iodothiobenzanilide derivatives at room temperature. The protocol is high-yielding and involves very mild conditions.
Y. Cheng, Q. Peng, W. Fan, P. Li, J. Org. Chem., 2014, 79, 5812-5819.

A copper-catalyzed, one-pot, three-component reaction of 1-iodo-2-nitroarenes with sodium sulfide and an aldehyde gives 2-substituted 1,3-benzothiazoles in good yields.
J. Liu, Q. Gui, Z. Yang, Z. Tan, R. Guo, J.-C. Shi, Synthesis, 2013, 45, 943-951.

In the presence of CuI and 1,10-phen, and n-Pr3N as the base, (2-iodobenzyl)triphenylphosphonium bromide and (2-iodophenylimino)triphenylphosphorane reacted efficiently with thiocarboxylic acids to give benzo[b]thiophenes and benzothiazoles in good yields via sequential Ullmann-type C-S bond coupling and subsequent Wittig reaction.
H. Yu, M. Zhang, Y. Li, J. Org. Chem., 2013, 78, 8898-8899.

An efficient oxidative cyclization of 2-aminophenols or 2-iodoanilines with alkenes provides diverse benzoxazoles/benzothiazoles in good yields in the presence of elemental sulfur.
J. Zhang, L. Hu, Y. Liu, Y. Zhang, X. Chen, Y. Luo, Y. Peng, S. Han, B. Pan, J. Org. Chem., 2021, 86, 14485-14492.

Iodine catalyzes simple and practical syntheses of 2-aroylbenzothiazoles and 2-arylbenzothiazoles from 2-aminobenzenethiols and acetophenones under metal-free conditions. Reactions in DMSO as oxidant and reaction medium provide 2-aroylbenzothiazoles, whereas the use of nitrobenzene as oxidant in dioxane as solvent enables the synthesis of 2-arylbenzothiazoles.
R. Ma, Y. Ding, R. Chen, Z. Wang, L. Wang, Y. Ma, J. Org. Chem., 2021, 86, 310-321.

A wide range of 2-aroylbenzothiazoles can be obtained in high yields by simply heating o-halonitrobenzenes, acetophenones, elemental sulfur, and N-methylmorpholine. This three-component coupling occurs in an excellent atom-, step-, and redox-efficient manner with elemental sulfur as nucleophile building block and redox moderating agent.
T. B. Nguyen, K. Pasturaud, L. Ermolenko, A. Al-Mourabit, Org. Lett., 2015, 17, 2562-2565.

A multipathway coupled oxidation/heterocyclization domino strategy enables an efficient synthesis of 2-acylbenzothiazoles from various substrates including arylethenes, arylacetylenes, 2-hydroxy-aromatic ketones and carbinols via four distinct pathways free of metal in one pot.
Y.-p. Zhu, F.-c. Jia, M.-c. Liu, A.-x. Wu, Org. Lett., 2012, 14, 4414-4417.

I2 and TBHP mediate a convenient synthesis of 2-acylbenzothiazoles in very good yields from acetophenones and benzothiazoles. The formal acylation of the benzothiazoles is achieved through a sequence involving formation of an aryl glyoxal, ring-opening of the benzothiazole followed by condensation of the amino group with the aryl glyoxal, cyclization and oxidation.
B. Wang, Q. Zhang, Z. Guo, K. Ablajan, Synthesis, 2020, 52, 3058-3064.

Various aromatic and heteroaromatic compounds have been efficiently thiocyanated by using a combination of bromodimethylsulfonium bromide (BDMS) and ammonium thiocyanate.
D. S. Bhalerao, K. G. Agamanchi, Synlett, 2007, 2952-2956.

An iron-catalyzed oxidative cyclization of 1-acyl-3-(phenyl)thioureas in the presence of sodium persulfate gave various N-benzothiazol-2-yl-amides selectively in good yields through C(sp2)-H functionalization and C-S bond formation.
J. Wang, Y. Zong, X. Zhang, Y. Gao, Z. Li, G. Yuo, Z. Quan, X. Wang, Synlett, 2014, 25, 2143-2148.

An ionic cascade insertion/cyclization reaction of thia-/selena-functionalized arylisocyanides enables an efficient and practical synthesis of 2-halobenzothiazole/benzoselenazole derivatives. Additionally, a facile access to 2-aminobenzothiazoles is also achieved by the one-pot cascade reaction of 2-isocyanoaryl thioethers, iodine, and amines.
J. Dong, J. Hu, X. Liu, S. Sun, L. Bao, M. Jia, X. Xu, J. Org. Chem., 2022, 87, 2845-2852.

The reaction of isothiocyanates with ortho-substituted anilines bearing N,N-, N,O-, and N,S-bis-nucleophiles, followed by an intramolecular, potassium periodate mediated oxidative cyclodesulfurization of the in situ generated monothioureas provides substituted 2-aminobenzazole derivatives in very good yields.
C. Duangkamol, W. Phakhodee, M. Pattarawarapan, Synthesis, 2020, 52, 1981-1990.

A tandem approach enables a facile and efficient synthesis of various 2-aminobenzothiazoles from 2-chloroanilines and dithiocarbamates in excellent yields in the presence of Pd(PPh3)4 and t-BuOK.
W. Xu, M.-T. Zeng, M. Liu, S.-S. Liu, Y.-S. Li, Z.-B. Dong, Synthesis, 2017, 49, 3084-3090.

A ruthenium catalyzed intramolecular C-S coupling reaction of N-arylthioureas enables the synthesis of 2-aminobenzothiazoles via an electrophilic ruthenation pathway instead of a direct C-H activation. In case of meta-substituents on the N-arylthiourea, stereoelectronic effects dictate the final regioselective outcome of the reaction.
S. Sharma, R. S. Pathare, A. K. Maurya, K. Gopal, T. K. Roy, D. M. Sawant, R. T. Pardasani, Org. Lett., 2016, 18, 356-359.

A nickel-catalyzed intramolecular oxidative C-H bond functionalization of arylthioureas provides 2-aminobenzothiazoles in very good yields and short reaction times. This protocol features an inexpensive catalyst, low catalyst loading, mild reaction conditions, and can be scaled up easily to a gram scale.
M.-Y. Gao, J.-H. Li, S.-B. Zhang, L.-J. Chen, Y.-S. Li, Z.-B. Dong, J. Org. Chem., 2020, 85, 493-500.

A catalytic amount of iodine enables a metal-free synthesis of 2-aminobenzothiazoles from cyclohexanones and thioureas in the presence of molecular oxygen as the oxidant under mild conditions. Various 2-aminobenzothiazoles, 2-aminonaphtho[2,1-d]thiazoles, and 2-aminonaphtho[1,2-d]thiazoles were prepared in satisfactory yields.
J. Zhao, H. Huang, W. Wu, H. Chen, H. Jiang, Org. Lett., 2013, 15, 2604-2607.

N-Arylthioureas are converted to 2-aminobenzothiazoles via intramolecular C-S bond formation/C-H functionalization in the presence of an unusual cocatalytic Pd(PPh3)4/MnO2 system under an oxygen atmosphere at 80°C. This method eliminates the need for an ortho-halo substituted precursor, instead achieving direct functionalization of the ortho-aryl C-H bond.
L. L. Joyce, R. A. Batey, Org. Lett., 2009, 11, 2792-2795.

2-Aminobenzthiazole is a privileged scaffold with a range of biological activities. Using anilines as starting materials, a highly efficient and mild protocol enables the synthesis of 2-aminiobenzthiazoles in the presence of NaICl2.
V. N. Telvekar, H. M. Bachhav, V. K. Bairwa, Synlett, 2012, 23, 2219-2222.

A cascade reaction of isothiocyanatobenzenes with primary or secondary amines provides 2-aminobenzothiazoles using iodine as a catalyst and oxygen as an oxidant via formation of a benzothiourea intermediate followed intramolecular cross dehydrogenative coupling. This method eliminates the use of ortho-halo-substituted precursors, expensive transition-metal catalysts, and hazardous oxidants.
Y. Xu, B. Li, X. Zhang, X. Fan, J. Org. Chem., 2017, 82, 9637-9646.

A transition-metal-free and scalable C-N coupling protocol achieves the synthesis of 2-aminobenzothiazoles from 2-chlorobenzothiazoles and primary amines under solvent-free conditions. Moreover, introducing an appropriate amount of NaH completely switched the selectivity from mono- toward di-heteroarylation.
H. Cheng, Y.-Q. Zhu, P.-F. Liu, K.-Q. Yang, J. Yan, W. Sang, X.-S. Tang, R. Zhang, C. Chen, J. Org. Chem., 2021, 86, 10288-10302.

An efficient copper-based catalytic system (Cu/PTABS) enables an amination of a chloroheteroarenes at ambient temperature in water as the sole reaction solvent. A wide variety of chloroheteroarenes could be coupled efficiently with primary and secondary amines as well as selected amino acid esters under mild reaction conditions.
U. Parmar, D. Somvanshi, S. Kori, A. A. Desai, R. Dandela, D. K. Maity, A. R. Kapdi, J. Org. Chem., 2021, 86, 8900-8925.

An efficient strategy for the synthesis of various 2-mercaptobenzothiazole derivatives proceeds from o-haloaniline derivatives and carbon disulfide via a tandem reaction in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to afford the corresponding 2-mercaptobenzothiazole derivatives in good yields.
F. Wang, S. Cai, Z. Wang, C. Xi, Org. Lett., 2011, 13, 3202-3205.

Lawesson’s reagent is an efficient promoter in the solvent-free microwave-assisted synthesis of 2-substituted benzoxazoles and benzothiazoles from carboxylic acids and 2-aminophenol or 2-aminothiophenol, respectively. Various aromatic, heteroaromatic and aliphatic carboxylic acids react under the conditions developed with good yields.
J. A. Seijas, M. P. Vázquez-Tato, M. R. Carballido-Reboredo, J. Crecente-Campo, L. Romar-López, Synlett, 2007, 313-316.

A general method for the formation of benzoxazoles and benzothiazoles via a copper-catalyzed cyclization of ortho-haloanilides is reported. Optimal conditions for cyclization used a catalyst combination of CuI and 1,10-phenanthroline as ligand. The mechanism is believed to proceed via an oxidative insertion/reductive elimination pathway through a Cu(I)/Cu(III) manifold. The rate of reaction of ortho-haloanilides follows the order I > Br > Cl, consistent with oxidative addition being the rate-determining step.
G. Evindar, R. A. Batey, J. Org. Chem., 2006, 71, 1802-1808.

A set of benzimidazoles, 3H-imidazo[4,5-b]pyridines, purines, xanthines and benzothiazoles was readily prepared from (hetero)aromatic ortho-diamines or ortho-aminothiophenol and aldehydes using chlorotrimethylsilane in DMF as a promoter and water-acceptor agent, followed by oxidation with air oxygen.
S. V. Ryabukhin, A. S. Plaskon, D. M. Volochnyuk, A. A. Tolmachev, Synthesis, 2006, 3715-3726.

A new, mild, and efficient method for the synthesis of 2-substituted benzothiazoles proceeds via the intramolecular cyclization of thioformanilides by using hypervalent iodine reagents in CH2Cl2 at ambient temperature.
D. S. Bose, M. Idrees, J. Org. Chem., 2006, 71, 8261-8263.

A novel metal-free iodine-mediated intramolecular oxidative cyclization protocol allows the preparation of various 2-substituted benzothiazoles.
D.-Y. Zhao, X.-K. Guo, J.-H. Li, R.-Y. Zang, Synthesis, 2012, 44, 927-933.

A transition-metal-free, DDQ-mediated method enables the intramolecular S-arylation of o-halobenzothiaoureas to yield 2-aminobenzothiazole derivatives. The reactions are performed at room temperature under base-free conditions with very good yields.
R. Wang, W.-j. Yang, L. Yue, W. Pan, H.-y. Zeng, Synlett, 2012, 23, 1643-1648.

The use of alkyl diacyl peroxides and alkyl tert-butyl peresters, which are readily accessible from carboxylic acids, enables an efficient, iron-catalyzed C-H alkylation of benzothiazoles. This reaction is environmentally benign and compatible with a broad range of functional groups. Various primary, secondary, and tertiary alkyl groups can be efficiently incorporated.
K. R. Babu, N. Zhu, H. Bao, Org. Lett., 2017, 19, 46-49.

A Cu(II)-catalyzed oxidative decarboxylation of phenylacetic acids and α-hydroxyphenylacetic acids enables the synthesis of various 2-aryl benzothiazoles in good yields from 2-unsubstituted benzothiazoles in the presence of oxygen as the sole oxidant. The reaction proceeds via Cu(II)-catalyzed decarboxylation, C-H bond oxidation, ring-opening, and condensation steps in one-pot and tolerates various functional groups.
Q. Song, Q. Feng, M. Zhou, Org. Lett., 2013, 15, 5990-5993.

A highly efficient Pd/Cu-catalyzed C-H arylation method for a range of heterocycles has been discovered. The efficiency and low loading of a combination of a palladium catalyst and a well-defined copper cocatalyst together with the mild reaction conditions demonstrate this method to be practically useful and mechanistically interesting.
J. Huang, J. Chan, Y. Chen, C. J. Borths, K. D. Baucom, R. D. Larsen, M. M. Faul, J. Am. Chem. Soc., 2010, 132, 3674-3675.

A Regel-type transition-metal-free direct C-2 aroylation of (benzo)oxazoles, (benzo)thiazoles and 1,3,4-oxadiazoles with acid chlorides is catalyzed by N,N-dimethyl-4-aminopyridine (DMAP) and affords the corresponding 2-keto­azoles in good yields.
P. Lassalas, F. Marsais, C. Hoarau, Synlett, 2013, 24, 2233-2240.

A simple and straightforward method for the direct carboxylation of aromatic heterocylces such as oxazoles, thiazoles, and oxadiazoles using CO2 as the C1 source requires no metal catalyst and only Cs2CO3 as the base. A good functional group tolerance is achieved.
O. Vechorkin, N. Hirt, X. Hu, Org. Lett., 2010, 12, 3567-3569.