One-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles by silica supported-zinc bromide in the aerobic condition

Ali Keivanloo; Mohammad Bakherad; Sayed Ali Naghi Taheri; Shahrzad Samangooei

doi:10.1016/j.crci.2012.11.007

One-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles by silica supported-zinc bromide in the aerobic condition

Ali Keivanloo ¹ ; Mohammad Bakherad ¹ ; Sayed Ali Naghi Taheri ¹ ; Shahrzad Samangooei ¹

¹ School of Chemistry, Shahrood University of Technology, Daneshgah avenue, Shahrood 3619995161, Iran

Comptes Rendus. Chimie, Volume 16 (2013) no. 3, pp. 239-243.

Résumé

An efficient one-pot cross-coupling/1,3-dipolar cycloaddition sequence was developed for a convenient synthesis of 4,5-disubstituted-1,2,3-(NH)-triazoles, starting from various acid chlorides, terminal alkynes and sodium azide in the presence of silica supported-zinc bromide under aerobic conditions.

Métadonnées

Reçu le : 2012-05-09
Accepté le : 2012-11-15
Publié le : 2013-01-05

DOI : 10.1016/j.crci.2012.11.007

Mots clés : Copper free, Cross-coupling, Dipolar cycloaddition, 1, 2, 3-(NH)-triazoles, Silica supported, Aerobic condition, Zinc bromide

Affiliations des auteurs :

Ali Keivanloo ¹ ; Mohammad Bakherad ¹ ; Sayed Ali Naghi Taheri ¹ ; Shahrzad Samangooei ¹

¹ School of Chemistry, Shahrood University of Technology, Daneshgah avenue, Shahrood 3619995161, Iran

@article{CRCHIM_2013__16_3_239_0,
     author = {Ali Keivanloo and Mohammad Bakherad and Sayed Ali Naghi Taheri and Shahrzad Samangooei},
     title = {One-pot synthesis of 4,5-disubstituted {1,2,3-(NH)-triazoles} by silica supported-zinc bromide in the aerobic condition},
     journal = {Comptes Rendus. Chimie},
     pages = {239--243},
     publisher = {Elsevier},
     volume = {16},
     number = {3},
     year = {2013},
     doi = {10.1016/j.crci.2012.11.007},
     language = {en},
}

TY  - JOUR
AU  - Ali Keivanloo
AU  - Mohammad Bakherad
AU  - Sayed Ali Naghi Taheri
AU  - Shahrzad Samangooei
TI  - One-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles by silica supported-zinc bromide in the aerobic condition
JO  - Comptes Rendus. Chimie
PY  - 2013
SP  - 239
EP  - 243
VL  - 16
IS  - 3
PB  - Elsevier
DO  - 10.1016/j.crci.2012.11.007
LA  - en
ID  - CRCHIM_2013__16_3_239_0
ER  -

%0 Journal Article
%A Ali Keivanloo
%A Mohammad Bakherad
%A Sayed Ali Naghi Taheri
%A Shahrzad Samangooei
%T One-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles by silica supported-zinc bromide in the aerobic condition
%J Comptes Rendus. Chimie
%D 2013
%P 239-243
%V 16
%N 3
%I Elsevier
%R 10.1016/j.crci.2012.11.007
%G en
%F CRCHIM_2013__16_3_239_0

Ali Keivanloo; Mohammad Bakherad; Sayed Ali Naghi Taheri; Shahrzad Samangooei. One-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles by silica supported-zinc bromide in the aerobic condition. Comptes Rendus. Chimie, Volume 16 (2013) no. 3, pp. 239-243. doi : 10.1016/j.crci.2012.11.007. https://comptes-rendus.academie-sciences.fr/chimie/articles/10.1016/j.crci.2012.11.007/

Version originale du texte intégral

1 Introduction

1,2,3-triazoles are important nitrogen heterocyles which display many interesting properties including antibacterial [1], herbicidal, fungicidal [2], antiallergic [3], anti-HIV [4], GSK-3 inhibiting [5], and antineoplastic activities [6]. Moreover, they have been widely used in various research fields, such as biological [7], and material sciences [8], medicinal [9], and synthetic organic chemistry [10].

One-pot multi-step reactions have a number of advantages including minimizing waste, saving energy, and reducing operating times. This process is especially useful when the reaction intermediates are unstable and difficult to isolate. Recently, efforts have been developed for the synthesis of 1,2,3-triazoles by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) using a multi-step, one-pot synthetic approach [11]. Copper(I)-catalyzed 1,3-cycloaddition reaction often referred to as “click-chemistry” [12] offered an efficient route to the synthesis of 1,4-disubstituted-1,2,3-triazoles. Also the Ru-catalyzed reaction of terminal alkynes with alkyl azides was discovered to be a unique way to synthesize 1,5-disubstituted-1,2,3-triazoles [13]. In these methods inorganic azides, NaN₃ and KN₃ are not active enough under mild conditions and it is inconvenient to prepare 4,5-disubstituted 1,2,3-(NH)-triazoles. Only a few methods for the synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles have been reported [14]. It is therefore necessary to develop novel ways of synthesizing 4,5-disubstituted 1,2,3-(NH)-triazoles.

2 Results and discussion

Some new approachs for constructing 4,5-disubstituted 1,2,3-(NH)-triazoles are based on Sonogashira coupling reaction [15]. These methods are efficient, but they have several drawbacks, which include the requirements of expensive palladium catalyst, dry solvents, and inert atmosphere.

In this article, we report an efficient, one-pot, copper and palladium free method for the synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles 4 via cross coupling reaction/1,3-dipolar cycloaddition of acid chlorides 1, terminal alkynes 2 and sodium azide in the presence of silica supported-zinc bromide under aerobic conditions (Scheme 1).

Scheme 1
Synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles from various acid chlorides, terminal alkynes and sodium azide in the presence of silica supported-zinc bromide under aerobic conditions.

Recently we reported the synthesis of ynones by the cross-coupling reaction of acid chlorides with terminal alkynes in the presence of silica-supported zinc bromide (ZnBr₂/SiO₂) under solvent free conditions [16]. We decided to use the same procedure followed by 1,3-dipolar cycloaddition for the synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles.

In our starting experiment, phenyl acetylene, 4-chlorobenzoyl chloride, sodium azide were put in one-pot in the presence of ZnBr₂ (1.2 eq) and a base (DIPEA or Et₃N) in various solvents (CH₃CN, dioxane, THF, DMF) was added to the mixture and the reaction was carried out at room temperature for 10 h, after which the temperature was raised to 50 °C and the reaction was continued for a further 5 h. Unfortunately, only a very poor yield of the desired product were formed. But when the reaction of phenyl acetylene and 4-chlorobenzoyl chloride were carried out using ZnBr₂ (1.2 eq) or ZnBr₂/SiO₂ (10 mol%) catalyst in various solvents or under solvent free condition at room temperature, in advance, followed by sodium azide 1,3-dipolar cycloaddition at 50 °C, (4-bromophenyl)(5-phenyl-2H-1,2,3-triazol-4-yl)methanone, 4c was obtained in 62–96% isolated yield (Table 1). Optimization of the conditions was reached when ZnBr₂/SiO₂ (10 mol%) was used as the catalyst under solvent free condition at room tempreture followed by sodium azide cycloaddition in CH₃CN/H₂O (3:1) at 50 °C (Table 1, entry 7).


Entry	Solvent	Base	Catalyst	Cyloaddition solvent	Yield (%)
1	CH₃CN	DIPEA^b	ZnBr₂^c	CH₃CN/H₂O	76
2	CH₃CN	Et₃N	ZnBr₂	CH₃CN/H₂O	62
3	DMF	Et₃N	ZnBr₂	DMF/H₂O	78
4	DMF	DIPEA	ZnBr₂	DMF/H₂O	85
5	CH₃CN	DIPEA	SiO₂/ZnBr₂^e	CH₃CN/H₂O	80
6	DMF	DIPEA	SiO₂/ZnBr₂	DMF/H₂O	71
7	–^d	DIPEA	SiO₂/ZnBr₂	CH₃CN/H₂O	96
8	–^d	Et₃N	SiO₂/ZnBr₂	CH₃CN/H₂O	74
9	–^d	DIPEA	SiO₂/ZnBr₂	H₂O	90
10	–^d	DIPEA	SiO₂/ZnBr₂	DMSO/H₂O	70

^a Reaction conditions: p-chlorobenzoyl chloride (1.2 mmol), phenylacetylene (1.0 mmol), base (1.2 mmol), solvent (1 mL) and catalyst, stir room temperature (3 h), followed by sodium azid (1.2 mmol) addition in solvent, 50 °C (3 h).

^b Diisopropylethylamine.

^c 1.2 eq.

^d Without solvent.

^e 10 mol%.

In order to explore the scope and generality of this protocol, we examined various benzoyl chlorides and different 1-alkynes using the optimized procedure (Table 2). The results show that this reaction is equally facile with both electron-donating and electron-withdrawing substituents present on the benzoyl chloride, resulting in good-to-high yields of the corresponding triazoles. Aliphatic terminal alkynes also reacted smoothly, affording the desired product in 88–95% yield. The structure of compounds was established by spectroscopic data and elemental analysis.


Entry	R¹	R²	Product	Mp (°C)	Yield^b (%)	Ref
1	C₆H₅	C₆H₅	4a	114–116	92	[15a]
2	C₆H₅	C₃H₇	4b	85–87	94	[15a]
3	4-BrC₆H₄	C₆H₅	4c	92–94	95	New
4	4-ClC₆H₄	C₆H₅	4d	131–133	96	[15a]
5	2-ClC₆H₄	C₃H₇	4e	Oil	92	New
6	2-ClC₆H₄	C₆H₅	4f	Oil	91	[15a]
7	4-ClC₆H₄	C₃H₇	4g	75–77	93	New
8	4-MeC₆H₄	C₆H₅	4h	117–119	90	[15a]
9	2-MeC₆H₄	C₆H₅	4i	89–91	87	[15a]
10	2-MeC₆H₄	C₃H₇	4j	Oil	88	New
11	4-ClC₆H₄	C₆H₁₃	4k	Oil	94	New
12	4-NO₂C₆H₄	C₆H₅	4l	150–152	82	[15a]
13	2,4-Cl₂C₆H₄	C₆H₅	4m	68–70	96	New
14	4-ClC₆H₄	C₄H₉	4n	73–75	95	[15a]

^a Reaction conditions: benzoyl chloride (1.2 mmol), terminal alkyne (1.0 mmol), base (1.2 mmol), SiO₂/ZnBr₂ (10 mol%), stir room temperature (3 h), followed by addition of sodium azid (1.2 mmol), 50 °C (3 h).

^b Isolated yield.

The proposed mechanism for the steps involved in the reactions is shown in Scheme 2. The key step of the reaction is the cross-coupling reaction of terminal alkynes with benzoylchlorides to afford the ynone intermediate 3. Subsequent 1,3-dipolar cycloaddition with sodium azide completes the reaction mechanism.

Scheme 2
Proposed mechanism for the formation of 4,5-disubstituted-1,2,3-(NH)-triazoles, from acyl chlorides, terminal alkynes and sodium azide in the presence of silica supported-zinc bromide.

3 Conclusion

In conclusion, we have developed an efficient, facile, convenient, one-pot, copper and palladium free method for the synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles via cross-coupling reaction/1,3-dipolar cycloaddition of acid chlorides, terminal alkynes and sodium azide in the presence of silica supported-zinc bromide in aerobic conditions.

4 Experimental

All the reagents used were of general reagent grade. IR spectra were obtained as potassium bromide pellets or solvent in the range of 400–4000 cm⁻¹ on a Shimadzu Model 460 spectrometer. ¹H NMR spectra were recorded on a Brucker BRX 400 AVANCE spectrometer. Elemental analyses were performed on a Thermo Finnigan Flash EA microanalyzer.

4.1 Preparation of silica-supported zinc bromide

Silica gel (Wakogel C-100, 3.65 g) was added to a solution of ZnBr₂ (6 mmol, 1.35 g) in EtOH (20 ml), and the mixture was heated at reflux for 1 h. The solvent was removed on a rotary evaporator, and the product was dried under vacuum at 150 °C for 10 h. Inductively coupled plasma atomic absorption spectrometry (ICP) indicated that 1.2 mmol of ZnBr₂ was supported on 1 g of ZnBr₂/SiO₂.

4.2 General procedure for the preparation of 4,5-disubstituted 1,2,3-(NH)-triazoles (3a-n)

A test-tube was charged with the acyl chloride (1.2 mmol), a terminal alkyne (1.0 mmol), ZnBr₂/SiO₂ (0.1 g, 0.12 mmol), and DIPEA (1.2 mmol), and the mixture was stirred at room temperature for 3 h under anhydrous conditions. Upon completion of the coupling reaction (monitored by TLC), sodium azide (1.2 mmol) in CH₃CN/H₂O (3:1) (2 ml) was added and and the mixture was heated at 50 °C with stirring for a further 3 h. After completion of the reaction (monitored by TLC), the solvent was evaporated and residue extracted with CH₃CN. Concentrating the solution gave the crude product which was subjected to column chromatography using CHCl₃–CH₃OH (98:2) as eluent to obtain an analytically pure product. Characterization data for new compounds are given below.

4.3 (4-bromophenyl)(5-phenyl-2H-1,2,3-triazol-4-yl)methanone (4c)

¹H NMR (400 MHz, CDCl₃): δ7.85 (d, J = 8.0 Hz, 2H, ArH), 7.72 (d, J = 8.0 Hz, 2H, ArH), 7.67–7.47 (m, 5H, ArH), 5.77 (s, 1H, NH); ¹³C NMR (100 MHz, CDCl₃): δ 188.52, 132.72, 132.41, 132.20, 131.56, 130.53, 130.00, 129.93, 129.62, 129.41, 128.60. IR (KBr): 3290 (NH), 1640 (CO), 1590, 1560, 1490, 740 cm⁻¹; Anal. Calcd for C₁₅H₁₀BrN₃O: C, 54.90; H, 3.07; N, 12.80; Found: C, 54.88; H, 3.13; N, 12.78.

4.4 (2-chlorophenyl)(5-propyl-2H-1,2,3-triazol-4-yl)methanone (4e)

¹H NMR (400 MHz, DMSO-d₆): δ7.90 (d, J = 7.4 Hz, 1H, ArH), 7.46–7.75 (m, 3H, ArH), 6.82 (s, 1H, NH), 2.71 (t, J = 7.4 Hz, 2H, CH₂), 1.52 (m, 2H, CH₂), 0.98 (t, J = 7.6 Hz, 3H, CH₃); ¹³C NMR (100 MHz, DMSO-d₆): δ 187.61, 152.69, 142.74, 138.34, 136.85, 133.57, 131.20, 129.14, 127.82, 30.23, 20.66, 13.42. IR (KBr): 3300 (NH), 2920, 1680 (CO), 1590, 1420, 1320, 760 cm⁻¹; Anal. Calcd for C₁₂H₁₂ClN₃O: C, 57.72; H, 4.84; N, 16.83; Found: C, 57.70; H, 4.85; N, 16.85.

4.5 (4-chlorophenyl)(5-propyl-2H-1,2,3-triazol-4-yl)methanone (4g)

¹H NMR (400 MHz, DMSO-d₆): δ 8.10 (d, J = 8.3 Hz, 2H, ArH), 7.50 (d, J = 8.4 Hz, 2H, ArH,), 6.50 (s, 1H, NH), 2.94 (t, J = 7.6 Hz, 2H, CH₂), 1.60 (m, 2H, CH₂), 1.00 (t, J = 7.5 Hz, 3H, CH₃); ¹³C NMR (100 MHz, DMSO-d₆): δ 187.26, 153.70, 141.81, 139.56, 134.38, 131.82, 129.04, 30.22, 20.64, 13.55. IR (KBr): 3285 (NH), 2950, 1678 (CO), 1588, 1425, 1310, 750 cm⁻¹; Anal. Calcd for C₁₂H₁₂ClN₃O: C, 57.72; H, 4.84; N, 16.83; Found: C, 57.73; H, 4.83; N, 16.84.

4.6 (2-methylphenyl)(5-propyl-2H-1,2,3-triazol-4-yl)methanone (4j)

¹H NMR (400 MHz, DMSO-d₆): δ 7.66 (d, J = 7.7 Hz, 1H, ArH), 7.20–7.45 (m, 3H, ArH), 2.61 (t, J = 7.7 Hz, 2H, CH₂), 2.22 (s, 3H, CH₃), 1.68 (m, 2H, CH₂), 0.83 (t, J = 7.4 Hz, 3H, CH₃); ¹³C NMR (100 MHz, DMSO-d₆): δ 185.02, 152.80, 141.77, 140.23, 137.33, 132.58, 132.43, 131.62, 125.76, 29.88, 20.64, 20.33, 13.67. IR (KBr): 3300 (NH), 2950, 1640 (CO), 1540, 1445, 1380, 1240, 840, 750 cm⁻¹; Anal. Calcd for C₁₃H₁₅N₃O: C, 68.10; H, 6.59; N, 18.33; Found: C, 68.18; H, 6.61; N, 18.35.

4.7 (4-chlorophenyl)(5-hexyl-2H-1,2,3-triazol-4-yl)methanone (4k)

¹H NMR (400 MHz, DMSO-d₆): δ 7.82 (d, J = 8.3 Hz, 2H, ArH), 7.35 (d, J = 8.3 Hz, 2H, ArH), 2.62 (t, J = 6.8 Hz, 2H, CH₂), 1.58 (m, 2H, CH₂), 1.20 (m, 4H, 2CH₂), 0.82 (t, J = 6.4 Hz, 3H, CH₃); ¹³C NMR (100 MHz, DMSO-d₆): δ 187.26, 153.65, 142.00, 139.79, 134.48, 131.71, 128.93, 31.75, 30.85, 29.40, 27.52, 23.18, 14.13; IR (KBr): 3300 (NH), 2900, 1690 (CO), 1580, 1450, 1380, 1258, 750 cm⁻¹; Anal. Calcd for C₁₅H₁₈ClN₃O: C, 61.75; H, 6.22; N, 14.40; Found: C, 61.73; H, 6.23; N, 14.38.

4.8 (2,4-dichlorophenyl)(5-phenyl-2H-1,2,3-triazol-4-yl)methanone (4m)

¹H NMR (400 MHz, DMSO-d₆): δ 9.23 (s, 1H, NH), 8.14 (d, J = 8.5 Hz, 2H, ArH), 7.68 (s, 1H, ArH), 7.57–7.26 (m, 5H, ArH); ¹³C NMR (100 MHz, DMSO-d₆): δ 185.92, 153.37, 138.65, 138.08, 134.48, 133.82, 131.00, 130.60, 130.45, 129.35, 128.45, 128.13, 127.54; IR (KBr): 3293 (NH), 2900, 1648 (CO), 1590, 1540, 1380, 1320, 820, 780 cm⁻¹; Anal. Calcd for C₁₅H₉Cl₂N₃O: C, 56.63; H, 2.85; N, 13.21; Found: C, 56.65; H, 2.83; N, 13.22.

Bibliographie

[1] M.J. Genin; D.A. Allwine; D.J. Anderson; M.R. Barbachyn; D.E. Emmert; S.A. Garmon; D.R. Graber; K.C. Grega; J.B. Hester; D.K. Hutchinson; J. Morris; R.D. Reischer; D. Stper; B.H. Yagi; B.S. Holla; M. Mahalinga; M.S. Karthikeyan; B. Poojary; P.M. Akberali; N.S. Kumari Eur. J. Med. Chem., 43 (2000), p. 953

[2] H. Wamhoff (A.R. Katritzky; C.W. Rees, eds.), Comprehensive Heterocyclic Chemistry, 5, Pergamon, Oxford, 1984, p. 669

[3] D.R. Buckle; C.J.M. Rockell; H. Smith; B.A. Spicer; D.R. Buckel; D.J. Outred; C.J.M. Rockell; H. Smith; B.A. Spicer; D.R. Buckel; C.J.M. Rockell; H. Smith; B.A. Spicer J. Med. Chem., 29 (1986), p. 2262

[4] R. Alvarez; S. Velazquez; A. San-Felix; S. Aquaro; E. De Clercq; C.F. Perno; A. Karlsson; J. Balzarini; M.J. Camarasa J. Med. Chem., 37 (1994), p. 4194

[5] P.H. Olesen; A.R. Sørensen; B. Ursø; P. Kurtzhals; A.N. Bowler; U. Ehrbar; B.F. Hansen J. Med. Chem., 46 (2003), p. 3333

[6] N.A. Al-Masoudim; Y.A. Al-Soud Tetrahedron Lett., 43 (2002), p. 4021

[7] K. Sivakumar; F. Xie; B.M. Cash; S. Long; H.N. Barnhill; Q. Wang; N.J. Agard; J.A. Prescher; C.R. Bertozzi; A.D. Moorhouse; A.M. Santos; M. Gunaratnam; M. Moore; S. Neidle; J.E. Moses; R. Kumar; A. El-Sagheer; J. Tumpane; P. Lincoln; L.M. Wilhelmsson; T. Brown; V.D. Bock; D. Speijer; H. Hiemstra; J.H. van Maarseveen Org. Bio. Chem., 6 (2004), p. 4603

[8] V. Aucagne; K.D. Hänni; D.A. Leigh; P.J. Lusby; D.B. Walker; C.F. Ye; G.L. Gard; R.W. Winter; R.G. Syvret; B. Twamley; J.M. Shreeve; Q.C. Liu; P. Zhao; Y.M. Chen; H. Nandivada; X.W. Jiang; J. Lahann; S. Angelos; Y.W. Yang; K. Patel; J.F. Stoddart; J.I. Zink Angew. Chem., Int. Ed., 128 (2006), p. 2186

[9] R. Manetsch; A. Krasiski; Z. Radi; J. Raushel; P. Taylor; K.B. Sharpless; H.C. Kolb; J. Wang; G. Sui; V.P. Mocharla; R.J. Lin; M.E. Phelps; H.C. Kolb; H.R. Tseng; A. Sugawara; T. Sunazuka; T. Hirose; K. Nagai; Y. Yamaguchi; H. Hanaki; K.B. Sharpless; S. Omura; H. Chen; J.L. Taylor; S.R. Abrams; G.C. Tron; T. Pirali; R.A. Billington; P.L. Canonico; G. Sorba; A.A. Genazzani Med. Res. Rev., 126 (2004), p. 12809

[10] S. Wacharasindhu; S. Bardhan; Z.K. Wan; K. Tabei; T.S. Mansour; Y. Liu; W. Yan; Y. Chen; J.L. Petersen; X. Shi; A.R. Katritzky; S. Bobrov; KirichenkoKostyantyn; Y. Ji; P.J. Steel; A.K. Reid; C.J. McHugh; G. Richie; D. Graham; A.K. Verma; J. Singh; R. Chaudhary; Q. Dai; W. Gao; D. Liu; L.M. Kapzes; X.J. Zhang Org. Chem., 131 (2009), p. 4174

[11] F. Friscourt; G.J. Boons; H. Soonho; B. Hoon; K. Sumin; K. Sanghee; V. Aucagne; D.A. Leigh; D. Kumar; V.B. Reddy; R.S. Varma Tetrahedron Lett., 12 (2010), p. 4936

[12] H.C. Kolb; M.G. Finn; K.B. Sharpless; V.V. Rostovtsev; L.G. Green; V.V. Fokin; K.B. Sharpless; C.W. Tornoe; C. Christensen; M.J. Meldal Org. Chem., 40 (2001), p. 2004

[13] L. Zhang; X. Chen; P. Xue; H.H.Y. Sun; I.D. Williams; K.B. Sharpless; V.V. Fokin; G. Jia; M.M. Majireck; S.M. Weinreb; B.C. Boren; S. Narayan; L.K. Rasmussen; L. Zhang; H. Zhao; Z.Y. Lin; G.C. Jia; V.V. Fokin; L.K. Rasmussen; B.C. Boren; V.V. Fokin Org. Lett., 127 (2005), p. 15998

[14] N.S. Zefirov; N.K. Chapovsksya; V.V. Kolesnikov; B. Quiclet-Sire; S.Z. Zard; S. Sengupta; H.F. Duan; W.B. Lu; J.L. Petersen; X.D. Shi Org. Lett., 17 (1971), p. 1001

[15] J.H. Li; D. Wang; Y.Q. Zhang; J.T. Li; B.H. Chen; N. Li; D. Wang; J. Li; W. Shi; C. Li; B. Chen Tetrahedron Lett., 11 (2009), p. 3024

[16] A. Keivanloo; M. Bakherad; B. Bahramian; S. Baratniain Tetrahedron Lett., 52 (2011), p. 1498

Commentaires - Politique