- Open Access
Diversity oriented one-pot three-component sequential synthesis of annulated benzothiazoloquinazolines
Organic and Medicinal Chemistry Letters volume 2, Article number: 10 (2012)
Annulated benzothiazoloquinazolines have been synthesized by a diversity oriented simple and convenient synthesis involving one-pot three-component reaction of substituted 2-aminobenzothiazoles with α-tetralone and aromatic/heteroaromatic aldehydes in ethanol in the presence of catalytic amount of triethylamine. The synthesized compounds have been characterized by their elemental analyses and spectral data.
The synthesis of fused heterocycles has attracted considerable interest in heterocyclic chemistry as the fusion of biodynamic heterosystems has proved to be a very attractive and useful for the design of new molecular framework of potential drugs with varying pharmacological activities. A major challenge of modern drug discovery is to design highly efficient chemical reaction sequences which provide molecules containing maximum complexity and structural diversity with interesting bioactivities in minimum number of synthetic steps. Recently, multicomponent reactions have attracted attention of chemical and pharmaceutical research and emerged as highly efficient and synthetically useful reactions for the preparation of structurally diverse drug- like heterocyclic compounds.
There has been an increasing interest in the chemistry of quinazolines [1–5] because of being present quinazoline heterocyclic system as a building block in many natural and synthetic products capable of exhibiting a wide variety of biological and pharmacological activities . Quinazolines have been reported to exhibit anti-inflammatory , antihypertensive , anticancer , antitumor  and antibacterial  activities. Quinazoline and its derivatives have recently been evaluated as antagonist of various biological receptors such as 5-HT5A  related disease calcitonin gene - related peptide  and vasopressin V3 receptors . Benzothiazole has also been an interesting heterocyclic system in drug research on account of significant biological activities of its fused derivatives [15–17]. Thiazoloquinazolines, have shown significant activity against cancer . Thiazoloquinazolines have also been identified as cyclin dependent kinase (CDK) and glycogen synthase kinase (GSK-3) inhibitors [19, 20].
Result and discussion
The syntheses of heterocycles with fused heterosystems involve, in most of the cases, multistep synthetic methods which require a large number of synthetic operations including extraction and purification of each individual step. The multistep synthetic methodologies, therefore, led to the synthetic inefficiency with the generation of large amounts of waste. The methods reported in the literature [21, 22] for the synthesis of thiazoloquinazolines irrespective of positions of attachment of both the heterocyclic systems involved multisteps in which the formation of thiazole ring before the quinazoline ring induced low subsequent reactivity. Thiazoloquinazolines prepared by reaction of 2-aminobenzylamine with aromatic amine and then with 2-mercaptopropionic acid also involved multistep reaction. However, after detailed literature survey it was observed that there were only limited publications devoted to the synthesis of especially benzothiazoloquinazolines which involved cyclocondensation of 2-aminobenzothiazoles with Mannich bases obtained in the first step as a result of Mannich reaction . The multistep synthesis of benzothiazoloquinazolines suffered from some flaws including low yields, side products and tedious workup. In continuation of our research programme on the synthesis of nitrogen and sulphur containing novel heterocycles [24–31] of pharmaceutical interest and in view of the operational simplicity and intrinsic convergence (atom economy) of multicomponent reactions [32–36] in addition to their potential to introduce considerable structural diversity, we have synthesized annulated benzothiazoloquinazolines incorporating three biodynamic privileged heterosystems by a simple and convenient method involving multicomponent reaction of substituted 2-aminobenzothiazoles with α-tetralone and aromatic/heteroaromatic aldehydes in ethanol in the presence of catalytic amount of triethylamine, wherein 2-aminobenzothiazoles with both endocyclic nitrogen and exocyclic amino group participate as 1,3-binucleophile synthones in the formation of annulated benzothiazoloquinazolines (Scheme 1).
The reaction is believed to proceed to involve Knoevenagal condensation between α-tetralone and aromatic/heteroaromatic aldehyde in the initial step to form α,β- unsaturated ketone which undergoes Michael type addition with the nucleophilic endocyclic nitrogen of 2-aminobenzothiazole under the reaction conditions. The adduct formed is then cyclised intramolecularly with the lose of water molecule to provide annulated benzothiazolo[2,3-b] quinazolines. These reactions have taken place in one-flask domino manner and the enone system generated in situ immediately undergoes Michael type addition with 2-aminobenzothiazoles and subsequent cyclization. The possibility of formation of isomeric product involving nucleophilic attack of exocyclic amino group has been completely discarded on the basis of spectral characteristics. Annulated benzothiazoloquinazolines have also been synthesized by a multistep synthesis involving the reaction of substituted 2-aminobenzothiazoles with chalcones obtained by the reaction of α-tetralone with thiophene-2-carbaldehyde/p-methoxybenzaldehyde in the presence of catalytic amount of triethylamine. It has been observed that with the use of chalcones the reaction occurs in two steps relatively in longer time (6-8 h) with the moderate yields (50-60%) of annulated benzothiazoloquinazolines. But when the chalcones are replaced by their synthetic precursors, α-tetralone and thiophene-2-carbaldehyde/p-methoxybenzaldehyde, annulated benzothiazoloquinazolines are obtained with excellent yields (75-85%). The synthesized annulated benzothiazoloquinazolines are presented in table 1.
The structures of the synthesized compounds were confirmed by their elemental analyses and spectral data. Infrared spectra of all the synthesized compounds exhibit an intense unsaturation absorption band in the region 1605-1610 cm-1 (C = C). The absorption band in the region 1620-1654 cm-1 in the IR spectra of all the compounds indicated the presence of C = N bond. Two absorption bands corresponding to asymmetric and symmetric stretching vibrations of -NH2 group, which were present in the IR spectra of 2-aminobenzothiazoles, are absent in the IR spectra of the synthesized compounds. 1H NMR spectra of the synthesized compounds showed a multiplet in the region δ 7.01-8.08 ppm due to aromatic protons. The singlet appeared in the region δ 5.90-6.80 was assigned to the aliphatic proton (C7-H). The singlet observed in the region δ 3.69-3.84 ppm was attributed to the methoxy protons, whereas the methyl protons resonate as a singlet in the region δ 2.34-2.36 ppm in the 1H NMR spectra of annulated benzothiazoloquinazolines containing -OCH3 and -CH3 groups respectively. The multiplets observed in the region δ 2.74-3.23 ppm were assigned to the methylene protons at C-5 and C-6. In the 13C NMR spectra of the synthesized annulated benzothiazoloquinazolines, the δ values of most of the carbon atoms of CH3, CH2, CH, C = C, C = N, C-N, C-O, C-S, C-F and aromatic system could be determined by distinct resonance signals and were found to be in agreement with the proposed structures.
In conclusion, we have developed a simple and convenient diversity oriented one-pot three-component sequential synthesis for the synthesis of structurally diverse heterocycles, annulated benzothiazoloquinazolines, incorporating medicinally privileged heterosystems.
The present method with its mild reaction conditions and operational simplicity enables the sequential combination of three reactive components; α-tetralone, thiophene-2-carbaldehyde/p-methoxybenzaldehyde and 2-aminobenzothiazole in one-pot and efficiently incorporates structural diversity simply by varying the substituents or by slight structural modification in the components involved in the reaction. This new method has the advantages of higher yields, mild reaction conditions, shorter reaction time, and convenient procedure and can be extended to prepare a library of structurally diverse drug like small heterocyclic molecules.
Melting points were determined on an electric melting point apparatus and are uncorrected. The purity of all the compounds was checked by thin layer chromatography using various non-aqueous solvents. IR spectra (KBr pellets) were recorded on Shimadzu-8400S FT-IR Spectrophotometer. The 1H NMR and 13C NMR spectra were scanned on Jeol AL 300 FT NMR in CDCl3 using TMS as an internal standard. The chemical shifts are expressed as δ ppm.
Procedure for the preparation of 7-thien-2-yl/4'-methoxyphenyl-5, 6-dihydro-7H-benzo [h] benzothiazolo [2, 3-b] quinazolines
To a magnetically stirred solution of thiophene-2-carbaldehyde/p-methoxy benzaldehyde (0.01 mole) and α-tetralone (0.01 mole) in ethanol (20 ml), a catalytic amount of (C2H5)3N was added slowly and further stirred for 30 min. Then 2-aminobenzothiazole (0.01 mole) was added to the reaction mixture with stirring for 2 h and then refluxed for 60-90 min in a round bottom flask fitted with reflux condenser. The progress of the reaction was monitored by TLC. The precipitate formed after the completion of reaction was isolated by filtration. The solid separated out was washed well with ethanol, dried and finally crystallized from ethanol.
11-Methyl-7-(thien-2-yl)-5,6-dihydro-7H-benzo[h]benzothiazolo[2, 3-b]quinazoline (4a)
(4a). m.p. 210-212°C; yield: 76%; IR (KBr, cm-1): 3100, 2980, 1620, 1605; 1H NMR (300 MHz, CDCl3) δppm: 7.10-7.68 (m, 10H, Ar-H), 5.86 (s, 1H, C7), 3.18-3.23 (m, 2H, CH2), 2.93-3.05 (m, 2H, CH2), 2.36 (s, 3H, CH3); 13C NMR (75 MHz, CDCl3) δppm: 18.38, 26.98, 28.10, 58.32, 119.43, 122.13, 125.34, 125.53, 126.23,126.56, 126.85, 127.80, 127.32, 127.54, 128.26, 130.20, 132.14, 133.65, 134.12, 137.34, 139.14,143.15, 167.35; Anal. Calcd. for C23H18N2S2: C, 71.47; H, 4.69; N, 7.25; Found: C, 73.65; H, 4.99; N, 7.19.
11-Methoxy-7-(thien-2-yl)-5,6-dihydro-7H-benzo[h]benzothiazolo [2, 3-b] quinazoline (4b)
(4b) m.p. 220-222°C; yield: 80%, IR (KBr, cm-1): 3010-3080, 2975, 1620, 1615; 1H NMR (300 MHz, CDCl3) δppm: 7.09-7.84 (m, 10H, Ar-H), 5.98 (s, 1H,C7-H), δ 3.84 (s, 3H, OCH3), 2.96-3.22 (m, 4H, CH2, C5, and C6); 13C NMR (75 MHz, CDCl3) δppm: 26.9, 28.06, 54.60, 57.20, 115.70, 122.52, 125.29, 125.62, 126.14, 126.45, 127.58, 127.69, 128.08, 129.44, 130.68, 133.12, 133.28, 134.60, 137.20, 139.04, 142.98, 155.61, 167.19 Anal. Calcd. for C23H18N2OS2: C, 68.63; H, 4.51; N, 6.96; Found: C, 70.65; H, 4.35; N, 6.99.
9,10-Dichloro-7-(thien-2-yl)-5,6-dihydro-7H-benzo[h]benzothiazolo-[2, 3-b]quinazoline (4c)
(4c) m.p. 205-207°C; yield: 77%, IR (KBr, cm-1): 3060, 2972, 1622, 1615; 1H NMR (300 MHz, CDCl3) δppm: 7.08-7.45 (m, 9H, Ar-H), 5.96 (s, 1H,C7-H), δ 3.12-3.24 (m, 2H,CH2) 2.94-2.96 (m, 2H,CH2); 13C NMR (75 MHz, CDCl3) δppm: 26.96, 28.16, 57.23, 119.92, 120.32, 123.46, 125.13, 125.24, 126.23, 126.52, 127.26, 127.46, 128.13, 130.32, 131.82, 133.65, 134.91, 138.03, 139.45, 143.98, 167.16; Anal. Calcd. for C22H14Cl2N2S2: C, 59.86; H, 3.20; N, 6.35; Found: C, 62.09; H, 3.10; N, 6.45.
11-Fluoro-7-(thien-2-yl)-5,6-dihydro-7H-benzo[h]benzothiazolo-[2, 3-b]quinazoline (4d)
(4d) m.p. 190-192°C; yield: 75%, IR (KBr, cm-1): 3075, 2978, 1620, 1610; 1H NMR (300 MHz, CDCl3) δ ppm: 6.92-7.40 (m, 10H, Ar-H), 5.95 (s, 1H, C7-H), δ 3.18-3.23 (m, 2H,CH2) 3.01-3.05 (m, 2H, CH2); 13C NMR (75 MHz, CDCl3) δppm: 26.78, 28.13, 58.62, 119.23, 120.35, 122.16, 125.28, 125.69, 126.31, 126.65, 127.58, 127.67, 128.23, 131.98, 133.54, 134.46, 138.42, 139.68, 142.06, 153.72, 170.43; Anal. Calcd. for C22H15FN2S2: C, 67.67; H, 3.87; N, 7.17; Found: C, 67.65; H, 3.83; N, 7.13.
11-Methyl-7-(4-methoxyphenyl)-5,6-dihydro-7H-benzo[h]benzothiazolo[2, 3-b]quinazoline (4e)
(4e) m.p. 215-217°C; yield: 80%, IR (KBr, cm-1): 3045, 2977, 1650, 1610,1275 1H NMR (300 MHz, CDCl3) δppm: 7.20-7.54 (m, 11H, Ar-H), 5.90 (s, 1H, C7-H), 3.76 (s, 3H, OCH3), 2.94-3.01 (m, 2H, CH2), 2.80-2.86 (m, 2H, CH2), 2.26 (s, 3H, CH3); 13C NMR (75 MHz, CDCl3) δppm: 18.26, 26.98, 28.68, 54.92, 57.23, 113.74, 114.96, 115.26, 123.64, 125.32, 125.76, 126.23, 126.64, 127.19, 127.84, 128.68, 128.96, 130.05, 132.92, 133.30, 134.52, 143.42, 156.39, 169.30; Anal. Calcd. for C26H22N2OS: C, 76.07; H, 5.40; N, 6.82; Found: C, 76.01; H, 5.15; N, 6.92.
11-Methoxy-7-(4-methoxyphenyl)-5,6-dihydro-7H-benzo[h]benzothiazolo-[2, 3-b]quinazoline (4f)
(4f) m.p. 227-229°C; yield: 80%, IR (KBr, cm-1): 3100, 3080-3050, 1648, 1612; 1H NMR (300 MHz, CDCl3) δppm: 7.15-7.52 (m, 11H, Ar-H), 5.90 (s, 1H, C7-H), δ 3.73 (s, 3H, OCH3), 3.69 (s, 3H, OCH3), 2.94-3.00 (m, 2H, CH2), 2.80-2.86 (m, 2H, CH2); 13C NMR (75 MHz, CDCl3) δppm: 28.26, 28.95, 54.20, 55.09, 56.96, 115.52, 117.52, 119.32, 120.44, 125.18, 126.48, 127.32, 127.47, 127.80, 128.12, 128.76, 133.07, 133.40, 134.23, 136.35, 137.98, 153.62, 158.26, 169.39; Anal. Calcd. for C26H22N2O2S: C, 76.2; H, 5.2; N, 6.86; Found: C, 76.07; H, 5.40; N, 6.82.
9,10-Dichloro-7-(4-methoxyphenyl)-5,6-dihydro-7H-benzo[h]benzothiazolo[2, 3-b]quinazoline (4g)
(4g) m.p. 192-194°C; yield: 74%, IR (KBr, cm-1): 3008-3050, 2972, 1645, 1612, 1270; 1H NMR (300 MHz, CDCl3) δppm: 7.12-7.54 (m, 10H, Ar-H), 5.92 (s, 1H, C7-H), δ 3.73 (s, 3H,OCH3), 2.74-2.99 (m, 4H, CH2 at C5 and C6); 13C NMR (75 MHz, CDCl3) δppm: 26.98, 28.12, 55.08, 58.74, 115.26, 115.35, 119.62, 120.43, 125.63, 127.48, 127.32, 127.58, 128.11, 128.45, 128.69, 130.24, 131.67, 133.40, 133.86, 134.26, 144.53, 155.62, 167.38; Anal. Calcd. for C25H18Cl2N2OS: C, 64.49; H, 3.88; N, 6.06; Found: C, 64.52; H, 3.90; N, 6.02.
11-Fluoro-7-(4-methoxyphenyl)-5,6-dihydro-7H-benzo[h]benzothiazolo-[2, 3-b]quinazoline (4h)
(4h) m.p. 189-191°C; yield: 75%, IR(KBr, cm-1): 3010-3072, 2974, 1648, 1612, 1242; 1H NMR (300 MHz, CDCl3) δppm: 7.12-7.54 (m, 11H, Ar-H), 5.95 (s, 1H, C7-H), δ 3.69 (s, 3H, OCH3), 2.82-2.96 (m, 4H, CH2 at C5 and C6); 13C NMR (75 MHz, CDCl3) δppm: 26.98, 28.56, 55.63, 57.39, 115.47, 118.78, 119.12, 121.45, 125.73, 126.63, 127.32, 127.58, 128.16, 128.73, 128.97, 131.43, 133.26, 133.89, 134.38, 142.19, 153.76, 170.43; Anal. Calcd. for C25H19FN2OS: C, 72.40; H, 4.60; N, 6.72; Found: C, 72.44; H, 4.62; N, 6.76.
Witt A, Bergman J: Recent Developments in the field of quinazoline chemistry. Curr Org Chem 2003, 7: 659–677. 10.2174/1385272033486738
Connolly DJ, Cusack D, O'Sullivan TP, Guiry PJ: Synthesis of quinazolinones and quinazolines. Tetrahedron 2005, 61: 10153–10202. 10.1016/j.tet.2005.07.010
Michael JP: Quinoline, quinazoline and acridone alkaloids. Nat Prod Rep 1999, 16: 697–709. 10.1039/a809408j
Michael JP: Quinoline, quinazoline and acridone alkaloids. Nat Prod Rep 2002, 19: 742–760. 10.1039/b104971m
Michael JP: Quinoline, quinazoline and acridone alkaloids. Nat Prod Rep 2003, 20: 476–493. 10.1039/b208140g
Maritinei-Viturro CM, Dominguez D: Synthesis of the antitumoural agents batracylin and related isoindolo[1,2-b]quinazoline-12(10H)-ones. Tetrahedron Lett 2001, 48: 1023–1026.
Alagarsamy V, Raja SV, Dhanabal K: Synthesis and pharmacological evaluation of some 3-phenyl-2-substituted-3H-quinazolin-4-one as analgesic, anti-inflammatory agents. Bioorg Med Chem 2007, 15: 235–241. 10.1016/j.bmc.2006.09.065
Alagarsamy V, Pathak US: Synthesis and antihypertensive activity of novel 3-benzyl-2-substituted-3H-[1,2,4]triazolo[5,1-b]quinazolin-9-ones. Bioorg Med Chem 2007, 15: 3457–3462. 10.1016/j.bmc.2007.03.007
Murugan V, Kulkarni M, Anand RM, Kumar EP, Suresh B, Reddy VM: Synthesis of 2-[bis-2(chloroethyl)amino}methyl]-6,8-dinitro-1-(4-substituted phenyl)-1H-quinazolin-4-one derivatives as possible antineoplastic agents. Asian J Chem 2006, 18: 900–906.
Godfrey AAA: Preparation of Quinazolin-4-ones via Cyclization of N-(cyanophenyl) acetamide Derivatives. PCT Int Appl WO 2005012260 A2. Chem Abstr 2005. 142, 198095, 10 Feb 2005
Selvam P, Girija K, Nagarajan G, De Clerco E: Synthesis, antibacterial, and anti-HIV activities of 3-[5-amino-6-(2,3-dichloro-phenyl)-[1,2,4]triazin-3-yl]-6,8- dibromo-2-substi tuted-3H-quinazolin-4-one. Indian J Pharm Sci 2005, 67: 484–487.
Alanine A, Gobbi LC, Kolczewski S, Luebbers T, Peters JU, Steward L: Preparation of 8-Alkoxy or Cycloalkoxy-4-methyl-3,4-dihydro-quinazolin-2-ylamines for Treating 5-HT5A Receptor Related Diseases. US Patent 2006293350 A1. Chem Abstr 2006. 146,100721, 28 Dec 2006
Chaturvedula PV, Chen L, Civiello R, Degnan AP, Dubowchik GM, Han X, Jiang XJ, Macor JE, Poindexter GS, Tora GO, Luo G: Preparation of Piperidine-1-carboxamideDerivatives and Spirocycles Thereof as Antagonists of Calcitonin Gene-relatedPeptide Receptors. US Patent 2007149503 A1. Chem Abstr 2007. 147,118256. 28 Jun 2007
Letourneau J, Riviello C, Ho KK, Chan JH, Ohlmeyer M, Jokiel P, Neagu I, Morphy JR, Napier SE: Preparation of 2-(4-Oxo-4H-quinazolin-3-yl)acetamides as Vasopressin V3 Receptor Antagonists. PCT Int Appl WO 2006095014 A1. Chem Abstr 2006. 145,315012, 14 Sep 2006
Molinski TF: Marine pyridoacridine alkaloid: Structure, synthesis and biological chemistry. Chem Rev 1993, 93: 1825–1838. 10.1021/cr00021a009
Robin M, Fature R, Perichaud A, Galy JP: Synthesis of new thiazolo[5,4-a]acridine derivatives. Heterocycles 2000, 53: 387–395. 10.3987/COM-99-8794
Khan RH, Rastogi RC: Condensed heterocycles: synthesis and antifungal activities of pi-deficient pyrimidines linked with pi-rich heterocycles. J Agricult Food Chem 1991, 39: 2300–2303. 10.1021/jf00012a042
Grasso S, Micale N, Anna-aria Monforte, Monforte P, Polimeni S, Zappala M: Synthesis and in vitro antitumour activity evaluation of 1-aryl-1H,3Hthiazolo[4,3-b]quinazolines. Eur J Med Chem 2000, 35: 115–1119.
Testard A, Picot L, Lozach O, Blairvacq M, Meijer L, Murillo L, Piot JM, Thiery V, Besson T: Synthesis and evaluation of the antiproliferative activity of novel thiazolquinazolinone kinase inhibitors. J Enzyme Inhib Med Chem 2005, 20: 557–568. 10.1080/14756360500212399
Testard A, Loge C, Leger B, Robert JM, Lozach O, Blairvacq M, Meijer L, Thiery V, Besson T: Thiazolo[5,4-f]quinazolin-9-ones, inhibitors of glycogen synthase kinase-3. Bioorg Med Chem Lett 2006, 16: 3419–3423. 10.1016/j.bmcl.2006.04.006
Alexandre FR, berecibar A, Wrigglesworth R, Besson T: Efficient synthesis of thiazoloquinazolinone derivatives. Tetrahedron Lett 2003, 44: 4455–4458. 10.1016/S0040-4039(03)01026-8
Besson T, Guillard J, Rees CW: Multistep synthesis of thiazoloquinazolines under microwave irradiation in solution. Tetrahedron Lett 2000, 41: 1027–1030. 10.1016/S0040-4039(99)02221-2
Quiroga J, Hernández P, Insuasty B, Abonía R, Cobo J, Sánchez A, Nogueras M, Low NL: Control of the reaction between 2-aminobenzothiazoles and Mannich bases. Synthesis of pyrido[2,1-b][1,3]benzothiazoles versus [1,3]benzothiazolo[2, 3-b]quinazolines. J Chem Soc Perkin Trans 2002, 1: 555–559.
Rathore BS, Kumar M: Synthesis of 7-chloro-5-trifluoromethyl/7-fluoro/7-trifluoromethyl-4H-1,4-benzothiazines as antimicrobial agents. Bioorg Med Chem 2006, 14: 5678–5682. 10.1016/j.bmc.2006.04.009
Rathore BS, Gupta V, Gupta RR, Kumar M: Synthesis of 7-chloro-5-trifluoromethyl/7-fluoro/7-trifluoromethyl-4H-1,4-phenothiazines. Heteroatom Chem 2007, 18: 81–86. 10.1002/hc.20235
Kumar M, Sharma K, Samarth RM, Kumar A: Synthesis and antioxidant activity of quinolinobenzothaizinones. Eur J Med Chem 2010, 45: 4467–4472. 10.1016/j.ejmech.2010.07.006
Arya AK, Kumar M: An efficient green chemical approach for the synthesis of structurally diverse spiroheterocycles with fused heterosystems. Green Chem 2011, 13: 1332–1338. 10.1039/c1gc00008j
Arya AK, Kumar M: Base catalyzed multicomponent synthesis of spiroheterocycles with fused heterosystems. Mol Divers 2011, 15: 781–789. 10.1007/s11030-011-9309-2
Dandia A, Arya K, Khaturia S, Jain AK: Microwave-induced preparation of biologically important benzothiazolo[2, 3-b]quinazolines, and comparison with ultrasonic and classical heating. Monatsh Chem 2010, 141: 979–985. 10.1007/s00706-010-0361-x
Sharma BK, Sharma PK, Kumar M: One-Pot, Multicomponent Sequential Synthesis of Benzothiazoloquinazolinones. Synth Commun 2010, 40: 2347–2352. 10.1080/00397910903243807
Dandia A, Khaturia S, Jain AK, Arya K: Statement of a methodology for the microwave-induced preparation of biologically important benzothiazolo [2, 3-b] quinazolines and its comparison with ultrasonic and classical heating. 12th International Electronic Conference on Synthetic Organic Chemistry ECSOC-12 2008. 1–30 November 2008 [http://www.usc.es/congresos/ecsoc/11/ECSOC11.htm]
Nefzi A, Ostresh JM: The Current status of heterocyclic combinatorial liberies. Chem Rev 1997, 97: 449. 10.1021/cr960010b
Roth HJ, Kleemann A: In pharmaceutical chemistry. In Drug Synthesis. Volume 1. New York: Wiley; 1988.
Zhu J: Recent developments in the isonitrile-based multicomponent synthesis of heterocycles. Eur J Org Chem 2003, 7: 1133–1144.
Orm RVA, de Greef M: Recent advances in solution phase multicomponent methodology for the synthesis of heterocyclic compounds. Synthesis 2003, 10: 1471–1499.
Domling A, Ugi I: Multicomponent reaction with isocyanides. Angew Chem Int Ed 2000, 39: 3168–3210. 10.1002/1521-3773(20000915)39:18<3168::AID-ANIE3168>3.0.CO;2-U
The authors were thankful to the Head, Department of Chemistry, University of Rajasthan, Jaipur for providing laboratory and instrumentation facilities. RSIC, CDRI, Lucknow is also acknowledged for providing analytical and spectral data of the compounds. One of the authors (KS) thanks University of Rajasthan Jaipur (India) for the research fellowship.
The authors declare that they have no competing interests.
Authors’ original submitted files for images
Below are the links to the authors’ original submitted files for images.
About this article
Cite this article
Kumar, M., Sharma, K. & Sharma, D.K. Diversity oriented one-pot three-component sequential synthesis of annulated benzothiazoloquinazolines. Org Med Chem Lett 2, 10 (2012) doi:10.1186/2191-2858-2-10
- cyclic ketones