Categories: Synthesis of N-Heterocycles, Synthesis of S-Heterocycles >

Synthesis of thiazoles and benzothiazoles

Recent Literature

Treatment of N,N-diformylaminomethyl aryl ketones with phosphorus pentasulfide and triethylamine in chloroform gives 5-arylthiazoles in good yield. The 5-aryl-1,3-thiazole core has been successfully functionalised at the 2-position to yield, over two steps, a large array of 5-aryl-2-arylsulfonyl-1,3-thiazoles.
P. W. Sheldrake, M. Matteucci, E. McDonald, Synlett, 2006, 460-462.

2-Amino-4-alkyl- and 2-amino-4-arylthiazole-5-carboxylates and their selenazole analogues were synthesized by α-halogenation of β-keto esters with N-bromosuccinimide, followed by cyclization with thiourea or selenourea, respectively, in the presence of β-cyclodextrin in water at 50°C.
M. Narender, M. S. Reddy, V. P. Kumar, B. Srinivas, R. Sridhar, Y. V. D. Nageswar, K. R. Rao, Synthesis, 2007, 3469-3472.

Endothiopeptides can easily be obtained via Ugi reaction using thio acids as acid components. If isonitriles with an acetal group are applied, the endothiopeptides can directly be converted into thiazoles using TMSCl-NaI under microwave irradiation.
U. Kazmaier, S. Ackermann, Org. Biomol. Chem., 2005, 3, 3184-3187.

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.

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.

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.

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.

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.

Thionation of amides, 1,4-diketones, N-(2-oxoalkyl)amides, and N,N'-acylhydrazines with the use of a fluorous Lawesson's reagent leads to thioamides, thiophenes, 1,3-thiazoles, and 1,3,4-thiadiazoles in high yields. The isolation of the final products is achieved in most cases by a simple filtration.
Z. Kaleta, B. T Makowski, T. Soos, R. Dembinski, Org. Lett., 2006, 8, 1625-1628.

A new method for a direct, copper-catalyzed arylation of heterocycle C-H bonds by aryl iodides allows the conversion of electron-rich five-membered heterocycles and electron-poor pyridine oxides. The best results are obtained by using a combination of lithium tert-butoxide as base and copper iodide as catalyst.
H.-Q. Do, O. Daugulis, J. Am. Chem. Soc., 2007, 129, 12404-12405.