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Archives of Applied Science Research, 2010, 2 (5):392-397

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ISSN 0975-508X CODEN (USA) AASRC9

One-pot synthesis of 2 ­ phenylimidazo [4, 5-f] [1, 10] phenanthroline derivatives under solvent free conditions by using iodine

Syed shahed ali* Organic Research Laboratory, Department of Sir Sayyed College, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, India

ABSTRACT 2 - Phenylimidazo[4, 5-f][1, 10]phenanthrolines could be obtained in excellent yields by the onepot three-component condensation of 1, 10 phenanthroline-5,6-dione, aldehyde and ammonium acetate in the presence of catalytic amount of the inexpensive, readily available iodine under solvent-free condition. The mixture was ground together in a mortar with a pestle at room temperature for short reaction time and easy operation under solvent free condition. Keywords: 2-Phenylimidazo[4,5-f] [1,10]phenanthrolines, aldehydes, iodine, ammonium acetate.

INTRODUCTION To design and conduct chemical reaction with "green" experimental protocol is an enormous challenge that chemists have to confront to improve the quality of the environment for present and future generations. Target areas for achieving this goal are the exploration of alternative reaction conditions and reaction media to accomplish the desired chemical transformations with minimized by-products or waste, and elimination of the use of conventional organic solvents, wherever possible. Traditional chemical syntheses or transformations generally require volatile and often hazardous organic solvents as reaction media to facilitate mass and heat transfer, and to isolate and purify desired product from reaction mixtures. Over the past several years, chemists have been aware of the environmental implications of their chemistry. Nowadays, they are trying to develop new synthetic methods, reaction conditions, and uses of chemicals that reduce risks to humans and the environment. Organic solvent are high on the list of damaging chemicals because they are employed in huge amounts and are usually volatile liquids that are difficult to store. In recent years, solid-state organic reactions have caused great interest. They have many advantages such as high efficiency and selectivity, easy separation and purification, and mild 392 Scholar Research Library

Syed shahed ali Arch. Appl. Sci. Res., 2010, 2 (5): 392-397 _____________________________________________________________________________________ reaction conditions and benefit industry as well as the environment[1]. Many articles about solidstate reactions with grinding have been reported, such as the Grignard reaction[2], aldol condensations[3], and other reactions[4].Imidazole ring system is one of the most important substructures found in a large number of natural products and pharmacologically active compounds such as antiulcerative agent cimetidine[5] the proton pump inhibitor omeprazole[6] and the benzodiazepine antagonist flumazenil[7] are imidazole derivatives. In addition, the substituted imidazole ring systems are substantially used in ionic liquids [8] that have been given a new approach to `Green Chemistry'. Due to their great importance, many synthetic strategies have been developed. In 1882, Radziszewski and Japp reported the first synthesis of the imidazole from 1,2-dicarbonyl compound, various aldehydes and ammonia, to obtain the 2,4,5triphenyl imidazoles[9,10]. Also, Grimmett et.al. proposed the synthesis of the imidazole using nitriles and esters[11]. Recently, there are several methods reported in the literature for the synthesis of 2, 4, 5-triphenylimidazoles using zeolite HY/silica gel[12], ZrCl4 [13], NiCl2.6H2O[14], ionic liquid[15], sodium bisulfite[16]. However, these methods require prolonged reaction time and exotic reaction condition. Thus, the development of a new method for the synthesis of imidazoles derivatives would be highly desirable. In recent years, iodine has gained special attention as a catalyst in organic synthesis because many advantages such as excellent yield, uncomplicated handling, inexpensiveness, eco-friendly nature, readily available and high reactivity. Recently, several synthetically useful organic transformations using iodine as a catalyst have been reported in the literature [17, 18]. MATERIALS AND METHODS Synthesis of 2-phenyl-1H-imidazo [4, 5-f] [1, 10] phenanthroline (3) A mixture of benzaldehyde (1mmol), 1, 10- phenanthroline-5, 6-dione, (1 mmol), NH4OAC (2.5 mmol) and iodine 10 mmol% were ground together in a mortar with a pestle at room temperature for appropriate time (Table 2 ) . After completion of reaction confirmed by TLC, the mixture was treated with aq sodium thiosulphate to furnish the crude products. The crude was further purified by column chromatography by using methanol: benzene (25:75) eluent and recrystallised from methanol. 1,10-Phenanthroline-5,6-dione : Yellow solid mp. 260 0C; Yield 40% (4.6 g); 1H NMR (300MHz,DMSO-d6):H 7.58-7.62(dd, 2H), 8.49-852 (dd, 2H), 9.11-9.13 (dd, 2H); GC-MS: m/z = 211 (M+); Anal. Calcd for (C12H6N2O2)3(H2O): C,66.67; H, 3.11; N,12.96%. Found: C,67.22; H, 2.97; N, 12.99%. 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (1a): pale yellow solid; mp. 308 0C, 1H NMR (90MHz,CDCl3 DMSO-d6): H 13.48, (br., 1H), 9.04, (dd, 2H), 8.90,(d, 2H), 8.31, (d, 2H), 7.70, (dd, 2H), 7.49,(dd, 2H);LS-MS: m/z = 297 (M+). 2-(4-chlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (1b): pale yellow solid; mp. 307308 0C, 1H NMR (90MHz, CDCl3 DMSO-d6): H 13.49, (br.s, 1H), 9.06, (dd, 2H), 8.92, (d, 2H), 8.27, (d, 2H), 7.72, (dd, 2H), 7.53, (d, 2H); GC-MS: m/z = 332 (M+).

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Syed shahed ali Arch. Appl. Sci. Res., 2010, 2 (5): 392-397 _____________________________________________________________________________________ 4-(1H-imidazo[4,5-f][1,10] phenanthrolin-2-yl)Phenol (1c) : pale yellow solid; mp. 300 0C, IR (KBr, cm-1): 3392 (stretch OH); 1H NMR (90MHz, CDCl3 DMSO-d6): H 13.31, (br.s, 1H), 9.72, (s, 1H), 9.05, (d, 2H), 8.92, (d, 2H), 8.13, (d, 2H), 7.73, (dd, 2H), 6.97, (d, 2H); LS-MS: m/z = 313 (M+); Anal. Calcd for (C19H12N4O)2(H2O)3: C, 67.24; H, 4.45; N, 16.51%. Found: C, 67.20; H, 4.61; N, 16.07%. 2-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (1d): pale yellow solid; mp. 302 0C, IR (KBr, cm-1): 3397, 3108, 1606, 1541, 1384, 1198, 739; 1H NMR (90MHz, CDCl3 DMSO-d6): H 13.92, (br. s, 1H), 9.07, (d, 2H), 8.94, (d, 2H), 8.53, (d, 2H), 8.39, (d, 2H), 7.78, (dd, 2H); GC-MS: m/z = 342 (M+). RESULTS AND DISCUSSION As a part of our ongoing investigation in developing a versatile and efficient method for synthesis of heterocyclic compounds[17,18] we report here an efficient synthetic method for the synthesis of 2 - Phenylimidazo[4, 5-f][1, 10]phenanthrolines from 1,10 phenanthroline-5,6-dione, aldehyde and ammonium acetate in the presence of iodine (Scheme1).

CHO N N O + O X NH4OAC N N N NH X

I2

1

2 Scheme 1

3

Reaction were carried out simply by mixing 1, 10 phenanthroline-5, 6-dione with an aldehyde and ammonium acetate in the presence of a catalytic amount (15 mmol %) of iodine under solvent-free condition summarized in Table 2. The mixture was ground together in a mortar with a pestle at room temperature for short reaction time, and then purified by column chromatography, substituted imidazole derivatives were obtained in excellent yields. Accordingly, (10mmol%) was sufficient to catalyze the reaction. A rate enhancement with high yield was observed when higher molar ratios of iodine were used. However, no product formation was observed in absence of iodine. By getting this result, we have extended this protocol to a variety of aldehydes and ketones summarized in Table 1. This protocol is rapid and efficient for the preparation of several imidazoles from both electrons efficient as well as electron deficient aromatic aldehydes. Aliphatic aldehyde and ketones (e.g. acetaldehyde, acetone) were also used as starting carbonyl compounds for the same reaction. No product formation takes place in this reaction by grinding the reagents for more than 30 minutes. The phenyl groups substituted with different groups did not show any effect on the formation of imidazoles. The ortho and para substituents activate the aromatic ring of aldehydes and increase the rate of the reaction. While meta substitution requires somewhat greater time as compared to the o/p substituents. Heteroaromatic ketones reacted fast and gave excellent yields of desired imidazoles. A nearly stiochiometric amount of ammonium acetate was used in the course of the 394 Scholar Research Library

Syed shahed ali Arch. Appl. Sci. Res., 2010, 2 (5): 392-397 _____________________________________________________________________________________ reaction, whereas previously a many-fold excess of ammonium acetate was required. This is an additional advantage of the novel methodology. The possible mechanism of this reaction (Scheme 2). Table 1. I2 ­Catalyzed synthesis of 1, 10 phenanthroline-5, 6-diones Entry 1 Ketones1

N N O O

Aldehydes 2

CHO

Products 3

N N N H X

Yielda,b(%)

X

N

a. X- H b. X- 4-Cl c. X- 4-OH d. X- 4-NO2 e. X- 2-OH f. X- 3-NO2 g. X- 2-NO2 h. X- 4-CN i. X- 4-OMe j. X- 2,4,6-OMe k. X- 4-NMe 2 2

N N

95 95 91 94 93 89 95 94 91 90 94

N N N N H C C H H

HC C CHO H

O O

90

CHO

N N

N

3

N N

O O

OH

N OH N H

90

N

4

N N

O O

R-CHO

N N

N R N H

a. R- CH3CHO b.R-CH3COCH3

a

00 00

Yield of isolated pure products. bproducts were characterized by IR, NMR, Mass elemental analysis and comparison with authentic sample.

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Syed shahed ali Arch. Appl. Sci. Res., 2010, 2 (5): 392-397 _____________________________________________________________________________________ Table 2. Catalytic evolution for synthesis of 2b. X- 4-Cl under solvent free conditions. Entry 1 2 3 4 5 6

a

Time (min) 80 50 20 15 07 07

NH3

Yielda (%) 00 traces 20 85 95 95

I2 (mmol %) No 1 2 5 10 15

Isolated yield after column chromatography.

+ HOAC

NH4OAC

O

H

NH

+

X

..

NH3

X I

..

NH

N N

O

I2

+

..

NH3

-H2O

N N

II

O

I2

N N

O

..

I2

+

X

O

-I2

NH

NH

I2

N N

N

-H2O

N H X

N N

III

I2

O

N H NH2

-I2

(3)

X

Scheme 2 The acidic nature of molecular iodine makes it capable of binding with the carbonyl oxygen of aromatic aldehyde increasing the reactivity of the parent carbonyl compound and facilitates the formation of imines intermediate I. Further catalyst iodine condenses with the carbonyl oxygens of the ketone, which on dehydration afford the intermediate II. Intermediates I and II combine for the formation of intermediate III, which on dehydration and further cyclisation gives 1, 10 phenanthroline-5, 6-diones 3 in 89-95% yield (Scheme 2). CONCLUSION In conclusion, we have developed an efficient and convenient method for the synthesis of imidazole derivatives using cheap and readily available iodine as a catalyst. The notable merits offered by this methodology are solvent free reaction condtions, simple procedure, cleaner reactions, short reaction time and excellent yield of products.

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Syed shahed ali Arch. Appl. Sci. Res., 2010, 2 (5): 392-397 _____________________________________________________________________________________ Acknowledgement We wish to thank Md. Tilawat Ali the president of Sir Sayyed College for providing necessary facility for research work. REFERENCES [1] K. Tanaka, F. Toda, Chem. Rev. 2000, 100, 1025. [2] F. Toda, H. Takumi, H. Yamaguchi, Chem. Exp. 1989, 4, 507. [3] F. Toda, K. Tanaka, K. Hami, J. Chem. Soc., Perkin Trans. 1990, 1, 3207. [4] (a) T. Schmeyers, F. Toda, J. Boy, G. Kaupp, J. chem. Sco. Perkin Trans. 1998, 2, 989.(b) H. Hagiwara, S. obtsubo, M. Kato, Mol. cryst. Liq. Cryst. 1996, 279, 291.(c) M. Tranaka, K. Kobayashi, J. chem. Soc., chem.Coummun. 1998, 1965. (d) J. Im, J. Kim, S. Kim, B. Hahu, F. Toda, Tetrahedron Lett. 1997, 38, 451. [5] R.W. Brimblecombe, W.A.M. Duncan, G.J. Durant, J.C. Emmett, C.R. Ganellin, M.E. Parons, J. Int. Med. Res. 1975, 3, 86. [6] Y. Tanigawara, N. Aoyama, T. Kita, K. Shirakawa, F. Komada, M.K. Kasuga, Clin. Pharmacol. Ther. 1999, 66, 528. [7] W. Hunkeler, H. Mohler, L. Pieri, P. Polc, E.P. Bonetti, R. Cumin, R.W. Schffner, Nature 1981, 290, 514. [8] (a) P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. Eng. 2000, 39, 37872;(b) D. Bourissou, O. Guerret, F.T. Ggabbai, G. Bertrand, Chem. Rev. 2000, 100. [9] B. Radziszewski, Chem. Ber. 1882, 15, 1493. [10] F.R. Japp, H.H. Robinson, Chem.Ber. 1882, 15, 1268. [11] M.R. Grimmett, In Comprehensive Heterocyclic Chemistry II; A.R. Katritzky, C.W. Rees, E.F.V. Scriven, Pergamon: New York 1996, 3, 77. [12] S. Balalaie, A. Arabanian, M.S. Hashtroudi, Mont. Fur. Chem. 2000, 131, 945. [13] G.V.M. Sharma, Y. Jyothi, P.S. Lakshmi, Syn. Commun. 2006, 36, 2991. [14] M.M. Heravi, K. Bakhtiari, H.A.Oskooie, S.Taheri, J.Mol. Catal. A: Chem. 2007, 263, 279. [15] S.A. Siddiqui, U.C. Narkhede, S.S. Palimkar, T. Daniel, R.J. Lahoti, K.V. Srinivasan, Tetrahedron 2005, 61, 3539. [16] J.N. Sangshetti, N.D. Kokare, S.A. Kothakar, D.B. Shinde, Mont. Fur. Chem. 2008, 139, 125. [17] M. Kidwai, P. Mothsra, V. Bansal, R. Goyal, Mont. Fur. Chem. 2006, 137, 1189. [18] B. P. Bandgar, K. A. Shaikh, Tetrahedron Letters. 2003, 44, 1959-1961

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