Synthesis of thiazoles
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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.
Ligand-free Pd(OAc)2 catalyzes very efficiently the direct arylation of thiazole derivatives under very low catalyst concentration. Reactions with activated aryl bromides can be performed employing as little as 0.1-0.001 mol % catalyst, whereas some strongly deactivated or highly congested aryl bromides only give disappointing results.
J. Roger, F. Pogan, H. Doucet, J. Org. Chem., 2009, 74, 1179-1186.
Conditions for the palladium-catalyzed direct arylation of a wide range of heterocycles with aryl bromides employ a stoichiometric ratio of both coupling partners, as well as a substoichiometric quantity of pivalic acid, which results in significantly faster reactions. An evaluation of the influence of the nature of the aryl halide has also been carried out.
B. Liégault, D. Lapointe, L. Caron, A. Vlassova, K. Fagnou, J. Org. Chem., 2009, 74, 1826-1834.
Base-induced cyclization of active methylene isocyanides such as tosylmethyl isocyanide, ethyl isocyanoacetate, and arylmethyl isocyanides with methyl arene- and hetarenecarbodithioates enables an efficient synthesis of 4,5-disubstituted thiazoles. This synthesis is simple, rapid, and often avoids purification steps.
G. S. Lingaraju, T. R. Swaroop, A. C. Vinayaka, K. S. S. Kumar, M. P. Sadashiva, K. S. Ragappa, Synthesis, 2012, 44, 1373-1379.
1-sulfonyl-1,2,3-triazoles react with thionoesters in the presence of a rhodium(II) catalyst providing 3-sulfonyl-4-thiazolines, which subsequently aromatize into the corresponding 2,5-disubstituted thiazoles by elimination of the sulfonyl group.
T. Miura, Y. Funakoshi, Y. Fujimoto, J. Nakahashi, M. Murakami, Org. Lett., 2015, 17, 2454-2457.
Palladium(II) acetate catalyzes a highly selective construction of 4-substituted 2-aminothiazoles from vinyl azides and potassium thiocyanate, whereas iron(III) bromide promotes the formation of 4-substituted 5-thiocyano-2-aminothiazoles. Use of readily available starting materials, high selectivity, as well as mild reaction conditions make these practical methods particularly attractive.
B. Chen, S. Guo, X. Guo, G. Zhang, Y. Yu, Org. Lett., 2015, 17, 4698-4701.
A copper-catalyzed coupling of oxime acetates with isothiocyanates provides various 4-substituted and 4,5-disubstituted 2-aminothiazoles under mild reaction conditions via copper-catalyzed N-O bond cleavage, activation of vinyl sp2 C-H bonds, and C-S/C-N bond formations. The oxime acetates serve not only as substrate but also as single oxidant.
X. Tang, Z. Zhu, C. Qi, W. Wu, H. Jiang, Org. Lett., 2016, 18, 180-183.
A domino alkylation-cyclization reaction of propargyl bromides with thioureas and thiopyrimidinones allows the synthesis of 2-aminothiazoles and 5H-thiazolo[3,2-a]pyrimidin-5-ones, respectively. Domino reactions were performed under microwave irradiation leading to desired compounds in a few minutes and high yields.
D. Castagnolo, M. Pagano, M. Bernardini, M. Botta, Synlett, 2009, 2093-2096.
A small library of compounds with oxazole and thiazole scaffolds and structural diversity in both positions 2 and 5 has been synthesized. Double acylation of a protected glycine affords intermediate α-amido-β-ketoesters, which in turn can be dehydrated to afford 1,3-oxazoles or reacted with Lawesson’s reagent to furnish 1,3-thiazoles.
J. F. Sanz-Cervera, R. Blasco, J. Piera, M. Cynamon, I. Ibáñez, M. Murguía, S. Fustero, J. Org. Chem., 2009, 74, 8988-8996.
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.
Thiazoles were obtained in good yields by the reaction of 1H-1-(1′-alkynyl)-5-methyl-1,2,3-benziodoxathiole 3,3-dioxides with thioamides. The co-product, potassium 2-iodo-5-methylbenzenesulfonate, was recovered quantitatively by simple filtration of the reaction mixture, and was regenerated to 1H-1-(1′-alkynyl)-5-methyl-1,2,3-benziodoxathiole 3,3-dioxides to be reused.
Y. Ishiwata, H. Togo, Synlett, 2008, 2637-2641.
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.
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.
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.