Outline
Comptes Rendus

Efficient one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-ones from aromatic aldehydes and their one-pot oxidation to quinazolin-4(3H)-ones catalyzed by Bi(NO3)3·5H2O: Investigating the role of the catalyst
Comptes Rendus. Chimie, Volume 14 (2011) no. 10, pp. 944-952.

Abstract

An efficient and novel synthesis of 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones via one-pot, three-component reaction of isatoic anhydride, primary amines and aromatic aldehydes catalyzed by Bi(NO3)3·5H2O under solvent-free conditions is described. Oxidation of these 2,3-dihydroquinazolin-4(1H)-ones to their quinazolin-4(3H)-ones was also successfully performed in the presence of Bi(NO3)3·5H2O. This new method has the advantages of convenient manipulation, short reaction times, excellent yields, very easy work-up, and the use of commercially available, low cost and relatively non-toxic catalyst. The role of Bi(NO3)3·5H2O was also investigated in these transformations.

Supplementary Materials:
Supplementary material for this article is supplied as a separate file:

Metadata
Received:
Accepted:
Published online:
DOI: 10.1016/j.crci.2011.05.003
Keywords: Bismuth(III) nitrate pentahydrate, 2, 3-Dihydroquinazolin-4(1H)-ones, Quinazolin-4(3H)-ones, Solvent-free

Iraj Mohammadpoor-Baltork 1; Ahmad R. Khosropour 1; Majid Moghadam 1; Shahram Tangestaninejad 1; Valiollah Mirkhani 1; Saeid Baghersad 1; Arsalan Mirjafari 1

1 Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
@article{CRCHIM_2011__14_10_944_0,
     author = {Iraj Mohammadpoor-Baltork and Ahmad R. Khosropour and Majid Moghadam and Shahram Tangestaninejad and Valiollah Mirkhani and Saeid Baghersad and Arsalan Mirjafari},
     title = {Efficient one-pot synthesis of {2,3-dihydroquinazolin-4(1\protect\emph{H})-ones} from aromatic aldehydes and their one-pot oxidation to {quinazolin-4(3\protect\emph{H})-ones} catalyzed by {Bi(NO\protect\textsubscript{3})\protect\textsubscript{3}{\textperiodcentered}5H\protect\textsubscript{2}O:} {Investigating} the role of the catalyst},
     journal = {Comptes Rendus. Chimie},
     pages = {944--952},
     publisher = {Elsevier},
     volume = {14},
     number = {10},
     year = {2011},
     doi = {10.1016/j.crci.2011.05.003},
     language = {en},
}
TY  - JOUR
AU  - Iraj Mohammadpoor-Baltork
AU  - Ahmad R. Khosropour
AU  - Majid Moghadam
AU  - Shahram Tangestaninejad
AU  - Valiollah Mirkhani
AU  - Saeid Baghersad
AU  - Arsalan Mirjafari
TI  - Efficient one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-ones from aromatic aldehydes and their one-pot oxidation to quinazolin-4(3H)-ones catalyzed by Bi(NO3)3·5H2O: Investigating the role of the catalyst
JO  - Comptes Rendus. Chimie
PY  - 2011
SP  - 944
EP  - 952
VL  - 14
IS  - 10
PB  - Elsevier
DO  - 10.1016/j.crci.2011.05.003
LA  - en
ID  - CRCHIM_2011__14_10_944_0
ER  - 
%0 Journal Article
%A Iraj Mohammadpoor-Baltork
%A Ahmad R. Khosropour
%A Majid Moghadam
%A Shahram Tangestaninejad
%A Valiollah Mirkhani
%A Saeid Baghersad
%A Arsalan Mirjafari
%T Efficient one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-ones from aromatic aldehydes and their one-pot oxidation to quinazolin-4(3H)-ones catalyzed by Bi(NO3)3·5H2O: Investigating the role of the catalyst
%J Comptes Rendus. Chimie
%D 2011
%P 944-952
%V 14
%N 10
%I Elsevier
%R 10.1016/j.crci.2011.05.003
%G en
%F CRCHIM_2011__14_10_944_0
Iraj Mohammadpoor-Baltork; Ahmad R. Khosropour; Majid Moghadam; Shahram Tangestaninejad; Valiollah Mirkhani; Saeid Baghersad; Arsalan Mirjafari. Efficient one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-ones from aromatic aldehydes and their one-pot oxidation to quinazolin-4(3H)-ones catalyzed by Bi(NO3)3·5H2O: Investigating the role of the catalyst. Comptes Rendus. Chimie, Volume 14 (2011) no. 10, pp. 944-952. doi : 10.1016/j.crci.2011.05.003. https://comptes-rendus.academie-sciences.fr/chimie/articles/10.1016/j.crci.2011.05.003/

Version originale du texte intégral

1 Introduction

The development of efficient and selective synthetic transformations in one operation using readily available, inexpensive and environmentally-benign catalysts and reagents is of great interest in modern organic synthesis [1]. Therefore, in recent years, synthetic chemists have directed their researches toward the green synthesis. 2,3-Dihydroquinazolin-4(1H)-ones are important heterocyclic compounds that exhibit a broad range of pharmaceutical activities including antifertility, antibacterial, antitumor, antifungal, and also as a mono amine oxidase inhibitor [2–4]. Moreover, 2,3-dihydroquinazolin-4(1H)-one derivatives are the key intermediate for the synthesis of quinazolin-4(1H)-one compounds. Due to the significant interest in these heterocyclic compounds, a number of methods for their synthesis have been developed with varying degree of success but with some limitations [5–13].

2,3-Disubstituted quinazolin-4(3H)-ones are also important building blocks in the synthesis of many natural products which display a variety of biological and pharmaceutical activities [14–16]. Known examples of 2,3-dihydroquinazoline-4(1H)-one drugs are diproqualone I which is used for the treatment of inflammatory pain associated with osteoarthritis, and methaqualone II which has antimalarial effect and currently being used for the assessment of the abuse liability of sedative hypnotic drugs [16] (Scheme 1). Furthermore, quinazoline alkaloids are an important class of natural products which possess biological effects. Among them, pyrrolo[2,1-b]quinazoline alkaloids such as isaindigotone III, deoxyvasicinone IV and 8-hydroxydeoxyvasicinone V exhibit anti-inflammatory, antimicrobial and antidepressant activities. The related alkaloid mackinazolinone VI possesses a broad spectrum of pharmacological activities [17] (Scheme 1). In accordance with the significance of quinazolin-4(3H)-ones, several synthetic methods have been developed for the construction of this kind of fused heterocycles from suitable precursors [18–29].

Scheme 1

Structure of some quinazoline-based drugs.

In recent years, Bi(III) salts have attracted the attention of synthetic organic chemists as effective catalysts because of their low toxicity, ease of handling, low cost and relative insensitivity to air and moisture [30–32]. As a part of our continuing research on the development of environmentally friendly synthetic methods of important organic compounds [33–39] and also on the application of Bi(III) salts in organic synthesis [31,40–45], we would like to report a new, efficient and highly selective one-pot synthesis of 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones and their one-pot oxidation to quinazolin-4(3H)-ones using Bi(NO3)3·5H2O under solvent-free conditions (Scheme 2).

Scheme 2

Synthesis of 2,3-dihydroquinazolin-4(1H)-ones and quinazolin-4(3H)-ones.

2 Experimental

2.1 General

Melting points were obtained by Stuart Scientific SMP2 apparatus and are uncorrected. Yields refer to isolated products. IR spectra were recorded on FT-IR Nicolet 400D. 1H and 13C NMR (500 and 125 MHz) spectra were recorded on a Bruker-Avance AQS 500 spectrometer. Mass spectra were obtained on a platform II spectrometer from Micromass; EI mode at 70 eV. Elemental analysis was performed on LECO, CHNS-932. All products were characterized by their physical and spectral data.

2.2 General procedure for the synthesis of 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones

To a mixture of isatoic anhydride (1.1 mmol), aromatic aldehyde (1 mmol) and amine (1 mmol), Bi(NO3)3·5H2O (0.05 mmol) as catalyst was added. The mixture was heated at 80 °C for the appropriate time. The progress of the reaction was monitored by TLC (ethyl acetate/n-hexane, 1:3). After completion of the reaction, hot ethanol (15 mL) was added and the catalyst was removed by filtration. The pure 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-one was obtained by recrystallization from ethanol.

2.3 General procedure for the synthesis of 2,3-disubstituted quinazolin-4(3H)-ones

After completion of the reaction for producing 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-one (4), Bi(NO3)3·5H2O (0.65 mmol) was added to the reaction mixture. The mixture was heated at 100 °C for the appropriate time. The reaction progress was monitored by TLC (ethylacetate/n-hexane, 1:5). At the end of the reaction, hot ethanol (15 mL) was added and the mixture was filtered. The pure 2,3-disubstituted quinazolin-4(3H)-one was obtained by recrystallization from ethanol.

3 Results and discussion

3.1 Synthesis of 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones

Initially, as a model reaction, the three-component reaction of isatoic anhydride, ethyl amine and 4-chlorobenzaldehyde in the presence of Bi(NO3)3·5H2O was investigated under various conditions (Table 1). Different reaction temperatures and molar ratios of Bi(NO3)3·5H2O and reagents were examined. The best yield of the desired product 4a was obtained by carrying out the reaction with 1.1:1:1:0.05 of isatoic anhydride, ethyl amine, 4-chlorobenzaldehyde and Bi(NO3)3·5H2O at 80 °C for 1 h (Table 1, entry 3).

Table 1

Reaction of isatoic anhydride with 4-chlorobenzaldehyde and ethyl amine in the presence of Bi(NO3)3·5H2O under solvent-free conditiona.

EntryBi(NO3)3·5H2O (mmol)T (°C)Time (h)Yield (%)b
4a5a
10.05401400
20.05601700
30.05801950
40.05901905
50.07801905
60.1801855
70.158018010
80.510041080
90.710041085
10110041575
11c0.05 + 0.61001 + 1.51085
12c0.05 + 0.651001 + 1.5590
13c0.05 + 0.71001 + 1.5590

a Isatoic anhydride (1.1 mmol), ethyl amine (1 mmol) and 4-chlorobenzaldehyde (1 mmol).

b Isolated yield.

c Reaction was performed in two steps.

With these optimized conditions in hand, the reaction of isatoic anhydride with a wide range of structurally varied aldehydes and amines were examined (Table 2). Aromatic aldehydes containing various electron-donating and electron-withdrawing groups underwent the conversion smoothly to furnish the corresponding 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones in excellent yields (90–97%). It is important to note that the electronic properties of the substituents on the aromatic aldehydes had no obvious influence on the yields and reactions times. Heteroaromatic aldehydes such as 2-thiophenecarbaldehyde (Table 2, entries 13 and 21) and 2-pyridinecarbaldehyde (Table 2, entry 14) and also α,β-unsaturated aldehyde such as cinnamaldehyde (Table 2, entry 15) afforded the desired products in high yields. The experimental procedure for these transformations is remarkably simple and requires no toxic organic solvents. After completion of the reaction, the pure product was conveniently obtained by recrystallization from ethanol. Owing to the mild reaction conditions, several functional groups such as NO2, CN, OMe and C=C bond were found to be compatible. All these results clearly showed the efficiency of this catalytic system in the synthesis of 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones.

Table 2

Synthesis of 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones the presence of Bi(NO3)3·5H2O under solvent-free conditions.

EntryAldehydeAmineProductTime (h)Yield (%)aMp (°C)
1EtNH24a195132–135 [6]
2EtNH24b190146–149
3EtNH24c1.597158–161
4EtNH24d295129–131
5EtNH24e296160–161 [6]
6EtNH24f196176–178 [6]
7EtNH24g1.594155–158
8EtNH24h191170–172
9EtNH24i194124–126 [6]
10EtNH24j193112–116
11EtNH24k191146–149
12EtNH24l292140–143
13EtNH24m197126–128
14EtNH24n0.590128–130
15EtNH24o0.592132–134
16n-BuNH24p197150–151 [13]
17n-BuNH24q194135–138
18n-BuNH24r1.596137–139
19n-BuNH24s195102–105
20n-BuNH24t191144–146
21n-BuNH24u19599–101
22iso-BuNH24v295128–130
23iso-BuNH24w292137–139
24iso-BuNH24x295204–205
25iso-BuNH24y29265–69

a Isolated yield.

3.2 Synthesis of 2,3-disubstituted quinazolin-4(3H)-ones

It is noteworthy that in the synthesis of 2-(4-chlorophenyl)-3-ethyl-2,3-dihydroquinazolin-4(1H)-one 4a, the yield of the product was reduced by increasing the temperature and or by increasing the amount of Bi(NO3)3·5H2O (Table 1, entries 4–10). Under these conditions, in addition to 4a, 2-(4-chlorophenyl)-3-ethylquinazolin-4(3H)-one 5a was also produced. Encouraged by this result, we decided to prepare 2,3-disubstituted quinazolin-4(3H)-ones 5 by the reaction of isatoic anhydride 1 with aldehydes 2 and amines 3 in the presence of Bi(NO3)3·5H2O. In order to determine the best reaction conditions, the reaction of isatoic anhydride (1.1 mmol) with ethyl amine (1 mmol) and 4-chlorobenzaldehyde (1 mmol) in the presence of different amounts of Bi(NO3)3·5H2O was investigated. The experimental results showed that even in the presence of 1 mmol Bi(NO3)3·5H2O, the product 5a was obtained in only 75% yield after 4 h (Table 1, entry 10). In order to improve the yield, we decided to synthesize 5a via a two-step reaction (Table 1, entries 11–13). First, the reaction was carried out with isatoic anhydride, ethyl amine and 4-chlorobenzaldehyde in the presence of catalytic amount of Bi(NO3)3·5H2O (0.05 mmol) for 1 h at 80 °C. After nearly complete conversion to the corresponding 2,3-dihydroquinazolin-4(1H)-one 4a, as indicated by TLC, 0.65 mmol Bi(NO3)3·5H2O was added and the mixture was stirred for a further 1.5 h at 100 °C. Under these conditions, the desired product 5a was obtained in 90% yield (Table 1, entry 12). Higher amounts of the Bi(NO3)3·5H2O did not improve the yield of 5a (Table 1, entry 13). Under these conditions, various aldehydes and amines were reacted with isatoic anhydride in the presence of Bi(NO3)3·5H2O and the corresponding 2,3-disubstituted quinazolin-4(3H)-ones 5 were obtained in high yields (86–95%) (Table 3).

Table 3

One-pot synthesis of 2,3-disubstituted quinazolin-4(3H)-ones in the presence of Bi(NO3)3·5H2O under solvent-free conditions.

EntryAldehydeAmineProductTime (h)Yield (%)aMp (°C)
1EtNH25a2.590108–112 [47]
2EtNH25b395110–112
3EtNH25c2.594101–105
4EtNH25d391125–128 [48]
5EtNH25e292180–184
6EtNH25f489190–192 [47]
7EtNH25g3.592125–128
8n-BuNH25h2.59368–70
9n-BuNH25i29283–85
10n-BuNH25j390123–125
11n-BuNH25k2.59262–64
12n-BuNH25l2.59488–90
13n-BuNH25m2.595117–119
14n-BuNH25n3.58759–61
15iso-BuNH25o3.589111–114
16iso-BuNH25p3.586Oil
17iso-BuNH25q391109–112
18iso-BuNH25r3.590123–126

a Isolated yield.

The efficiency and applicability of this method has been compared with some of the previously reported methods in Table 4. As can be seen, the present method is superior in terms of yield, reaction time and the amount of catalyst.

Table 4

Comparison of the results obtained by Bi(NO3)3·5H2O with some of the preveviously reported reagents.

EntryProductConditionsTime (h)Yield (%)
1SSA (0.15 mmol), H2O, 80 °C [11]3.584
2SSA (0.2 mmol), solvent-free, 80 °C [11]580
3Bi(NO3)3·5H2O (0.05 mmol), solvent-free, 80 °C195
4KAl(SO4)2·12H2O (0.4 mmol), EtOH, reflux [6]580
5KAl(SO4)2·12H2O (0.52 mmol), H2O, reflux [6]170
6Bi(NO3)3·5H2O (0.05 mmol), solvent-free, 80 °C194
7p-TsOH (0.5 mmol), H2O, reflux [8]190
8p-TsOH (0.5 mmol), EtOH, reflux [8]382
9Bi(NO3)3·5H2O (0.05 mmol), solvent-free, 80 °C196

A possible mechanism for these reactions has been postulated in Scheme 3. First, isatoic anhydride 1 reacts with amine 2 to afford anthranilamide 6 by removing of carbon dioxide. Condensation of 6 with aldehyde in the presence of Bi(NO3)3·5H2O afforded the intermediate 7. Bi(NO3)3·5H2O catalyzes the tautomerization of amide group and also activates the imine group of this intermediate which is converted to intermediate 8. Cyclization of 8 to intermediate 9 via intramolecular nucleophilic attack of nitrogen to imin carbon followed by 1,5-proton shift gave the corresponding 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-one 4. Finally, the 2,3-dihydroquinazolin-4(1H)-one is oxidized to the corresponding quinazolin-4(3H)-one 5 in the presence of Bi(NO3)3·5H2O.

Scheme 3

Proposed mechanism.

In order to find the actual role of Bi(NO3)3·5H2O in the oxidation of 2,3-dihydroquinazolin-4(1H)-ones, some reactions were examined under different conditions. It has been reported that Bi(NO3)3·5H2O decomposes on heating [32,46] as shown in Scheme 4.

Scheme 4

Decomposition of Bi(NO3)3·5H2O on heating.

On the basis of this reaction, NO3, NO2, O2, combination of NO2 and O2, or O2 in the presence of Bi(NO3)3·5H2O catalyst may act as key oxidant. First the model reaction was investigated in only O2 in the absence of Bi(NO3)3·5H2O; no oxidation product was obtained under this conditions. This result clearly showed that O2 alone cannot be the effective oxidant. Then, this reaction was performed with Pb(NO3)2; the absence of any oxidation product proves that NO3 as well as a combination of NO2 and O2 are not the oxidant. On the other hand, the reaction did not proceed with BiCl3. It is also noteworthy that less than 5% of the oxidized product was obtained under argon atmosphere. In addition, regarding to the application of Bi(III)/O2 and Bi(III)/DMSO as oxidation systems in the literature, we found that most of these reactions have been carried out in DMSO and CH3CO2H solvents [31,40–44]. Therefore, the model reaction was performed in the presence of Bi(NO3)3·5H2O under these conditions. The results showed that only 5% and 38% of the corresponding quinazolin-4(3H)-one was obtained, respectively. Consequently, the method reported in this paper under solvent-free conditions is more convenient for the oxidation of 2,3-dihydroquinazolin-4(1H)-ones to their corresponding quinazolin-4(3H)-ones. All these observations indicate that the presence of oxygen is essential and Bi(NO3)3·5H2O has some catalytic effect in this oxidation reaction. Therefore, a combination of Bi(NO3)3·5H2O along with oxygen which is produced by the decomposition of this reagent and also provided from air acts as actual oxidizing system in these reactions.

4 Conclusion

In conclusion, we have demonstrated for the first time that Bi(NO3)3·5H2O could be used as an efficient catalyst for the selective synthesis of 2,3-disubstituted 2,3-dihydroquinazolin-4(1H)-ones and their one-pot oxidation to quinazolin-4(3H)-ones under solvent-free conditions. In addition, the advantages including high yields, short reaction times, easy work-up, green procedure avoiding toxic organic solvents, and the use of readily available, inexpensive and relatively non-toxic catalyst make the present method superior to the existing methods for the synthesis of quinazolinone derivatives.

Acknowledgements

Financial support of this work by Center of Excellence of Chemistry and Research Council of University of Isfahan is gratefully appreciated.


References

[1] N.K. Terrett; M. Gardner; D.W. Gordon; R.J. Kobylecki; J. Steele Tetrahedron, 51 (1995), p. 8135

[2] Y.S. Sadanandam; K.R.M. Reddy; A.B. Rao Eur. J. Med. Chem., 22 (1987), p. 169

[3] G. Bonola; E. Sianesi J. Med. Chem., 13 (1970), p. 329

[4] M.J. Hour; L.J. Huang; S.C. Kuo; Y. Xia; K. Bastow; Y. Nakanishi; E. Hamel; K.H. Lee J. Med. Chem., 43 (2000), p. 4479

[5] J.A. Moore; G.J. Sutherland; R. Sowerby; E.G. Kelly; S. Palermo; W. Webster J. Org. Chem., 34 (1969), p. 887

[6] M. Dabiri; P. Salehi; S. Otokesh; M. Baghbanzadeh; G. Kozehgarya; A.A. Mohammadi Tetrahedron Lett., 46 (2005), p. 6123

[7] A. Davoodnia; S. Allameh; A.R. Fakhari; N. Tavakoli-Hoseini Chinese Chem. Lett., 21 (2010), p. 550

[8] M. Baghbanzadeh; P. Salehi; M. Dabiri; G. Kozehgary Synthesis (2006), p. 344

[9] D. Shi; L. Rong; J. Wang; Q. Zhuang; X. Wang; H. Hu Tetrahedron Lett., 44 (2003), p. 3199

[10] M. Dabiri; P. Salehi; M. Baghbanzadeh Monatsh. Chem., 138 (2007), p. 1191

[11] M. Dabiri; P. Salehi; M. Baghbanzadeh; M.A. Zolfigol; M. Agheb; S. Heydari Catal. Commun., 9 (2008), p. 785

[12] J. Chen; W. Su; H. Wu; M. Liu; C. Jin Green Chem., 9 (2007), p. 972

[13] J. Chen; D. Wu; F. He; M. Liu; H. Wu; J. Ding; W. Su Tetrahedron Lett., 49 (2008), p. 3814

[14] S.B. Mhaske; N.P. Argade Tetrahedron, 62 (2006), p. 9787

[15] J.F. Wolfe; T.L. Rathman; M.C. Sleevi; J.A. Campbell; T.D. Greenwood J. Med. Chem., 33 (1990), p. 161

[16] K.V. Tiwari; R.R. Kale; B.B. Mishra; A. Singh Arkivoc, 14 (2008), p. 27

[17] J.F. Liu; P. Ye; K. Sprague; K. Sargent; D. Yohannes; C.M. Baldino; C.J. Wilson; S.C. Ng Org. Lett., 7 (2005), p. 3363

[18] T.M. Potewar; R.N. Nadaf; T. Daniel; R.J. Lahoti; K.V. Srinivasan Synth. Commun., 35 (2005), p. 231

[19] W.L.F. Armarego Adv. Heterocycl. Chem., 24 (1979), p. 1

[20] V. Segarra; M.I. Crespo; F. Pujol; J. Beleta; T. Domenech; M. Miralpeix; J.M. Palacios; A. Castro; A. Martinez Bioorg. Med. Chem. Lett., 8 (1998), p. 505

[21] M. Akazome; J. Yamamoto; T. Kondo; Y. Watanabe J. Organomet. Chem., 494 (1995), p. 229

[22] L.Y. Zeng; C. Cai J. Heterocycl. Chem., 47 (2010), p. 1035

[23] B. Venkat Lingaiah; G. Ezikiel; T. Yakaiah; G. Venkat Reddy; P. Shanthan Rao Synlett. (2006), p. 2507

[24] S.E. Lopez; M.E. Rosales; N. Urdaneta; M.V. Godoy; J.E. Charris J. Chem. Res. (S) (2000), p. 258

[25] J.J. Naleway; C.M.J. Fox; D. Robinhold; E. Terpetschnig; N.A. Olson; R.P. Haugland Tetrahedron Lett., 35 (1994), p. 8569

[26] B.A. Bhat; D.P. Sahu Synth. Commun., 34 (2004), p. 2169

[27] R. Abdel-Jalil; W. Voelter; M. Saeed Tetrahedron Lett., 45 (2004), p. 3475

[28] G.W. Wang; C.B. Miao; H. Kang Bull. Chem. Soc. Jpn, 79 (2006), p. 1426

[29] A.R. Khosropour; I. Mohammadpoor-Baltork; H. Ghorbankhani Tetrahedron Lett., 47 (2006), p. 3561

[30] H. Suzuki; T. Ikegami; Y. Matano Synthesis (1997), p. 249

[31] N.M. Leonard; L.C. Wieland; R.S. Mohan Tetrahedron, 58 (2002), p. 8373

[32] C. Mukhopadhyay; A. Datta Catal. Commun., 9 (2008), p. 2588

[33] I. Mohammadpoor-Baltork; H. Aliyan; A.R. Khosropour Tetrahedron, 57 (2001), p. 5851

[34] I. Mohammadpoor-Baltork; A.R. Khosropour Monatsh. Chem., 133 (2002), p. 189

[35] I. Mohammadpoor-Baltork; A.R. Khosropour; S.F. Hojati Synlett. (2005), p. 2747

[36] I. Mohammadpoor-Baltork; A.R. Khosropour; S.F. Hojati Monatsh. Chem., 138 (2007), p. 663

[37] I. Mohammadpoor-Baltork; M.M. Khodaei; K. Nikoofar Tetrahedron Lett., 44 (2003), p. 591

[38] M.M. Khodaei; I. Mohammadpoor-Baltork; H.R. Memarian; A.R. Khosropour; K. Nikoofar; P. Ghanbary J. Heterocycl. Chem., 45 (2008), p. 377

[39] A.R. Khosropour; I. Mohammadpoor-Baltork; M.M. Khodaei; P.Z. Ghanbary Z. Naturforsch., 62 (2007), p. 537

[40] V. Le Boisselier; C. Coin; M. Postel; E. Dunach Tetrahedron, 51 (1995), p. 4991

[41] S.H. Mashraqtu; C.D. Mudaliar; M.A. Karruk Synth. Commun., 28 (1998), p. 939

[42] S. Samajdar; F. Becker; B.K. Banik Synth. Commun., 31 (2001), p. 2691

[43] S.A. Tymonko; B.A. Nattier; R.S. Mohan Tetrahedron Lett., 40 (1999), p. 7657

[44] V. Le Boisselier; M. Postel; E. Dunach Chem. Commun. (1997), p. 95

[45] S. Rivera; D. Bandyopadhyay; B.K. Banik Tetrahedron Lett., 50 (2009), p. 5445

[46] N.N. Greenwood, A. Earnshaw, Chemistry of the elements, School of Chemistry, University of Leeds, UK, second ed., pp. 591.

[47] V.B. Rao; P. Hanumanthu; C.V. Ratnam Indian J. Chem., 18B (1979), p. 493

[48] S.C. Kou, M.J. Hour, L.J. Huang, K.H. Lee, 2002, US 6479499 B1.


Comments - Policy