Synthesis of-lactams from acids and imines using thiocarbonyldiimidazole

Article abstract of DOI:10.1080/00397911.2011.607935

Thiocarbonyldiimidazole has been found to be an efficient acid activator for the synthesis of-lactams by ketene-imine cycloaddition at room temperature. The experimental procedure is simple and results in excellent yields of the products. All products wer

Full text of DOI:10.1080/00397911.2011.607935

This article was downloaded by: [Dalhousie University]
On: 21 November 2012, At: 09:16
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Synthesis of β-Lactams from Acids and
Imines Using Thiocarbonyldiimidazole
Maaroof Zarei a , Zahed Karimi-Jaberi b & Amin Movahedi b
a Department of Chemistry, College of Sciences, Hormozgan
University, Bandar Abbas, Iran
b Department of Chemistry, Firoozabad Branch, Islamic Azad
University, Firoozabad, Fars, Iran
Accepted author version posted online: 27 Feb 2012.Version of
record first published: 13 Nov 2012.
To cite this article: Maaroof Zarei, Zahed Karimi-Jaberi & Amin Movahedi (2013): Synthesis of
β-Lactams from Acids and Imines Using Thiocarbonyldiimidazole, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 43:5, 728-734
To link to this article: http://dx.doi.org/10.1080/00397911.2011.607935
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Synthetic Communications1, 43: 728–734, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.607935
SYNTHESIS OF b-LACTAMS FROM ACIDS AND IMINES
USING THIOCARBONYLDIIMIDAZOLE
Maaroof Zarei,1 Zahed Karimi-Jaberi,2 and Amin Movahedi2
1Department of Chemistry, College of Sciences, Hormozgan University,
Bandar Abbas, Iran
2Department of Chemistry, Firoozabad Branch, Islamic Azad University,
Firoozabad, Fars, Iran
GRAPHICAL ABSTRACT
Abstract Thiocarbonyldiimidazole has been found to be an efficient acid activator for the
synthesis of b-lactams by ketene-imine cycloaddition at room temperature. The experi-
mental procedure is simple and results in excellent yields of the products. All products were
characterized by spectral data and elemental analyses.
Keywords 2-Azetidinones; ketene; b-lactams; Staudinger reaction; thiocarbonyldiimidazole
INTRODUCTION
b-Lactam antibiotics have occupied a central role in the fight against
pathogenic bacteria and the subsequent rise in quality of life for the world
population as a whole.[1] However, the extensive use of common b-lactam antibiotics
such as penicillins and cephalosporins in medicine has resulted in an increasing num-
ber of resistant strains of bacteria through mutation and b-lactamase gene transfer.[2]
The medicinal application of b-lactams as cholesterol absorption inhibitor has been
reported.[3] In addition, there are many important nonantibiotic uses of b-lactam
(2-azetidinone)[4] such as human cytomegalovirus (HCMV) inhibitor,[5] human leu-
kocyte elastase (HLE) inhibitor,[6] thrombin inhibitor,[7] porcine pancreatic elastase
(PPE) inhibitor,[8] HIV-1 protease inhibitor,[9] cysteine protease inhibitor,[10] antican-
cer drugs,[11] antifungals,[12] potential antimalarials,[13] anti-influenzavirus agents,[14]
antihyperglycemic compounds,[15] central nervous system (CNS) agents,[16] comba-
tants of neurological diseases,[17] and antiproliferative drugs.[18]
Received June 20, 2011.
Address correspondence to Maaroof Zarei, Department of Chemistry, College of Science,
Hormozgan University, Bandar Abbas, 71961, Iran. E-mail: maaroof1357@yahoo.com, mzarei@
hormozgan.ac.ir
728

SYNTHESIS OF b-LACTAMS FROM ACIDS AND IMINES
729
Scheme 1. The cycloaddition reaction of ketenes with imines.
These biological activities, combined with the use of b-lactams as starting
materials to prepare several organic and medicinal compounds,[19] provide motiv-
ation to explore new methodologies for the synthesis of substances based on the
b-lactam core.
Many synthetic methods were developed for the formation of the b-lactam
ring.[20] The Staudinger reaction,[21] reactions of ketenes with imines (Scheme 1), is
probably the most important synthetic tool to access b-lactams, and this reaction
is still one of the best means for the synthesis of b-lactams.[22]
The most common method for the in situ production of ketene derivatives is
the simple reaction of an acyl chloride with a tertiary amine as a base.[23] Because
of instability and difficulty in the preparation of acyl chloride, the use of some acti-
vator of carboxylic acids for in situ generation of the ketene has been reported.[24]
Thiocarbonyldiimidazole has been used previously for several organic
transformations.[25]
In this article we document the successful achievement of this goal and the
synthesis of b-lactams by the Staudinger reaction from imines and substituted
carboxylic acids using thiocarbonyldiimidazole as a simple and efficient method.
RESULTS AND DISCUSSION
The starting materials, Schiff bases 1a–d, were synthesized from correspond-
ing aldehydes and amines by condensation in ethanol at reflux. In a model study,
the solution of N-(4-chlorobenzylidene)-4-ethoxyaniline 1a and phenoxyacetic acid
in dry dimethylformamide (DMF) was treated with thiocarbonyldiimidazole and
dry triethylamine at room temperature. After extraction by chloroform, the usual
workup, and crystallization from 95% EtOH, b-lactam 3a was obtained as a
white solid with 44% yield. This successful result encouraged us to investigate
the optimum condition reactions. Then the effects of solvents, temperature of
reaction, and quantity of reagent in the synthesis of 3a were considered. Accord-
ing to Table 1, among the dry solvents examined, CH2Cl2 showed the best results.
Also the workup in CH2Cl2 does not need extraction by chloroform. We found
that the yields decreased at 0 ꢀC. The molar optimization of reagent showed
1.5 mmol of thiocarbonyldiimidazole was needed to complete the reaction
[thin-layer chromatographic (TLC) monitoring of the disappearance of the imine]
in CH2Cl2 at room temperature. The indicated cis stereochemistry of the product
was judged from the coupling constants of H-3 and H-4 of the b-lactam ring in
1H NMR (J > 4.0).
Based on the successful results, 2-azetidinones 3a–l were synthesized by treat-
ment of 1.0 mmol of Schiff bases, 1.5 mmol of acetic acid derivatives, and 1.5 mmol

730
M. ZAREI, Z. KARIMI-JABERI, AND A. MOVAHEDI
Table 1. Optimization of reaction condition in the synthesis of 3a
Entry
Solvent
Temperature (ꢀC)
Thiocarbonyldiimidazole (mmol)
Yield (%)
1
2
3
4
5
6
7
DMF
THF
rt
rt
rt
rt
0
1.5
1.5
1.5
1.5
1.5
1.3
1.1
44
58
94
47
70
81
55
CH2Cl2
Toluene
CH2Cl2
CH2Cl2
CH2Cl2
rt
rt
thiocarbonyldiimidazole in the presence of triethylamine in dry CH2Cl2 at room
temperature (Scheme 2, Table 2). b-Lactams 3a–l were purified by recrystallization
from EtOH. All products were characterized by spectral data and elemental analyses.
Scheme 2. Synthesis of 2-azetidinones 3a–1 using thiocarbonyldiimidazole.
Table 2. Synthesis of 2-azetidinones 3a–l
Product
R1
R2
R3
Yield (%)
3a
3b
3c
3d
3e
3f
4-EtOC6H4
4-EtOC6H4
4-MeOC6H4
4-EtOC6H4
4-EtOC6H4
4-EtOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
C6H5
4-ClC6H4
4-ClC6H4
4-ClC6H4
PhO
91
87
85
90
83
88
93
87
91
94
82
92
PhthN
MeO
PhO
4-MeC6H4
4-MeC6H4
4-MeC6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
PhthN
MeO
PhO
3g
3h
3i
PhthN
MeO
PhO
=
=
=
3j
C
C
C
C-C6H5
C-C6H5
C-C6H5
3k
3l
C6H5
C6H5
PhthN
MeO

SYNTHESIS OF b-LACTAMS FROM ACIDS AND IMINES
731
CONCLUSION
In conclusion, we have developed a convenient and efficient method for the
synthesis of 2-azetidinones; purification of products was performed with simple
aqueous workup and recrystallization from EtOH. All b-lactams have cis stereo-
chemistry, and the yields of products were good to excellent.
EXPERIMENTAL
All required chemicals were purchased from Merck and Acros chemical
companies. The melting points were determined on a Buchi 535 apparatus and are
uncorrected. Infrared (IR) spectra were measured on a Shimadzu Fourier transform
(FT)–IR 8300 spectrophotometer. NMR spectra were recorded on a Bruker spectro-
photometer (1H NMR 250 MHz, 13C NMR 62.9 MHz) using tetramethylsilane as an
internal standard, and coupling constants are given in cycles per second (Hz).
Elemental analyses were run on a Vario EL III elemental analyzer. TLC was carried
out on silica-gel 254 analytical sheets obtained from Merck. The data for Schiff bases
previously have been reported in the literature.[24a,b,26] Phthaloylglycine was pre-
pared by a reported method.[27]
General Procedure for the Synthesis of 2-Azetidinones 3a–l Using
Thiocarbonyldiimidazole
Thiocarbonyldiimidazole (0.27 g, 1.5 mmol) was added to a solution of the
substituted acetic acid (1.5 mmol), corresponding Schiff base (1.0 mmol) and dry
triethylamine (0.51 g, 0.70 mL, 5.0 mmol) in 15 mL dry solvents [CH2Cl2, DMF,
tetrahydrofuran (THF), and toluene] at room temperature, and the mixture was stir-
red overnight. In the cases of DMF and THF, water was added, and extraction by
2 ꢁ 10 mL CHCl3 was performed. Then the organic solution was washed successively
with saturated NaHCO3 (20 mL) and brine (20 mL). The organic layer was dried
(Na2SO4) and filtered, and the solvent was removed under reduced pressure to give
the crude products. b-Lactams 3a–l were purified by recrystallization from EtOH.
1-(4-Methoxyphenyl)-4-(4-nitrophenyl)-3-phenoxyazetidin-2-one
(3g)
1
White solid (93%), mp: 195–197 ꢀC; IR (KBr) cmꢂ1: 1744 (CO, b-lactam); H
NMR (CDCl3) d 3.81 (OMe, s, 3H), 5.32 (H-4, d, 1H, J ¼ 4.6), 5.53 (H-3, d, 1H,
J ¼ 4.6), 6.77–7.49 (ArH, m, 13H); 13C NMR (CDCl3) d 56.3 (OMe), 60.9 (C-4),
82.7 (C-3), 113.4–160.1 (aromatic carbons), 161.7 (CO, b-lactam). Anal. calcd. for
C22H18N2O5: C, 67.69; H, 4.65; N, 7.18. Found: C, 67.61; H, 4.75; N, 7.14.
2-(1-(4-Methoxyphenyl)-2-(4-nitrophenyl)-4-oxoazetidin-
3-yl)isoindoline-1,3-dione (3h)
Light-yellow solid (87%), mp: 170–172 ꢀC. IR (KBr) cmꢂ1: 1736, 1773 (CO,
1
phth), 1784 (CO, b-lactam); H NMR (DMSO-d6) d 3.81 (OMe, s, 3H), 5.37 (H-4,

732
M. ZAREI, Z. KARIMI-JABERI, AND A. MOVAHEDI
d, 1H, J ¼ 4.8), 5.76 (H-3, d, 1H, J ¼ 4.8), 6.90–8.37 (ArH, m, 12H); 13C NMR
(DMSO-d6) d 58.3 (OMe), 60.7 (C-4), 63.2 (C-3), 113.4-157.5 (aromatic carbons),
162.3 (CO, phth), 165.4 (CO, b-lactam). Anal. calcd. for C24H17N3O6: C, 65.01;
H, 3.86; N, 9.48. Found: C, 64.93; H, 3.94; N, 9.42.
3-Methoxy-1-(4-methoxyphenyl)-4-(4-nitrophenyl)azetidin-2-one (3i)
Light-yellow crystalline solid (91%), mp: 133–135 ꢀC. IR (KBr) cmꢂ1: 1750
1
(CO, b-lactam); H NMR (CDCl3) d 3.28, 3.69 (2 OMe, 2 s, 6H), 4.88 (H-4, d,
1H, J ¼ 4.6), 5.37 (H-3, d, 1H, J ¼ 4.6), 6.72–7.64 (ArH, m, 8H); 13C NMR (CDCl3)
d 55.3, 57.5 (2 OMe), 64.1 (C-4), 82.6 (C-3), 115.7–159.3 (aromatic carbons), 161.8
(CO, b-lactam). Anal. calcd. for C17H16N2O5: C, 62.19; H, 4.91; N, 8.53. Found:
C, 62.28; H, 5.04; N, 8.58.
3-Phenoxy-1-phenyl-4-styrylazetidin-2-one (3j)
1
White solid (94%), mp: 185–187 ꢀC. IR (KBr) cmꢂ1:1749 (CO, b-lactam); H
NMR (CDCl3) d 4.90 (H-4, dd, 1H, J ¼ 4.9, 8.5), 5.37 (H-3, d, 1H, J ¼ 4.9), 6.23
(H-5, dd, J ¼ 8.5, 16.0), 6.75 (H-6, d, 1H, J ¼ 16.0), 6.87–7.38 (ArH, m, 14H); 13C
=
NMR (CDCl3) d 63.7 (C-4), 81.5 (C-3), 115.0-157.4 (C C, aromatic carbons),
162.2 (CO, b-lactam). Anal. calcd. for C23H19NO2: C, 80.92; H, 5.61; N, 4.10.
Found: C, 80.84; H, 5.70; N, 4.12.
2-(2-Oxo-1-phenyl-4-styrylazetidin-3-yl)isoindoline-1,3-dione (3k)
White solid (82%), mp: 196–198 ꢀC. IR (KBr) cmꢂ1: 1732, 1753 (CO, phth),
1
1779 (CO, b-lactam); H NMR (CDCl3) d 5.13 (H-4, dd, 1H, J ¼ 5.4, 8.8), 5.61
(H-3, d, 1H, J ¼ 5.4), 6.29 (H-5, dd, J ¼ 8.8, 15.9), 6.87 (H-6, d, 1H, J ¼ 15.9),
7.04–7.86 (ArH, m, 13H); 13C NMR (CDCl3) d 61.5 (C-4), 64.1 (C-3), 113.7–158.6
=
(C C, aromatic carbons), 163.8 (CO, phth), 166.5 (CO, b-lactam). Anal. calcd.
for C25H18N2O3: C, 76.13; H, 4.60; N, 7.10. Found: C, 76.20; H, 4.73; N, 7.16.
3-Methoxy-1-phenyl-4-styrylazetidin-2-one (3l)
White crystal solid (92%), mp: 101–03 ꢀC. IR (KBr) cmꢂ1: 1748 (CO,
1
b-lactam); H NMR (CDCl3) d 3.28 (OMe, s, 3H), 5.03 (H-4, dd, 1H, J ¼ 5.5,
8.5), 5.68 (H-3, d, 1H, J ¼ 5.5), 6.32 (H-5, dd, J ¼ 8.5, 16.0), 6.85 (H-6, d, 1H,
J ¼ 16.0), 7.19–7.82 (ArH, m, 10H); 13C NMR (CDCl3) d 57.7 (OMe), 61.0 (C-4),
=
82.1 (C-3), 118.6–155.8 (C C, aromatic carbons), 167.3 (CO, b-lactam); Anal. calcd.
for C18H17NO2: C, 77.40; H, 6.13; N, 5.01. Found: C, 77.49; H, 6.25; N, 4.95.
ACKNOWLEDGMENT
The authors thank the Islamic Azad University (Firoozabad Branch) Research
Council for financial support.

SYNTHESIS OF b-LACTAMS FROM ACIDS AND IMINES
733
REFERENCES
1. (a) Ceric, H.; Sindler-Kulyk, M.; Kovacevic, M.; Peric, M.; Zivkovic, A. Bioorg. Med.
Chem. 2010, 18, 3053–3058; (b) Hwu, J. R.; Ethiraj, K. S.; Hakimelahi, G. H. Mini-Rev.
Med. Chem. 2003, 3, 305–313; (c) Alcaide, B.; Almendros, P. in Topics in Heterocyclic
Chemistry; B. K. Banik (Ed.); Springer-Verlag: Berlin, 2010; Vol. 22, pp. 1–48.
2. (a) Granados, C. A.; Cardo, D. M.; McGowan, J. E. Int. J. Antimicrob. Agents 2008, 32,
1–9; (b) Hakimelahi, G. H.; Li, P.-C.; Moosavi-Movahedi, A. A.; Chamani, J.;
Khodarahmi, G. A.; Ly, T. W.; Valiyev, F.; Leong, M. K.; Hakimelahi, S.; Shia, K.-S.;
Chao, I. Org. Biomol. Chem. 2003, 1, 2461–2467.
3. (a) Xu, X.; Fu, R.; Chen, J.; Chen, S.; Bai, S. Bioorg. Med. Chem. Lett. 2007, 17, 101–104;
(b) Clader, J. W. Curr. Top. Med. Chem. 2005, 5, 243–256.
4. For review, see Mehta, P. D.; Sengar, N. P. S.; Pathak, A. K. Eur. J. Med. Chem. 2010, 45,
5541–5560.
5. Gerona-Navarro, G.; de Vega, J. P.; Garcia-Lopez, M. T.; Andrei, G.; Snoeck, R.;
Balzarini, J.; De Clercq, E.; Gonzalez-Muniz, R. Bioorg. Med. Chem. Lett. 2004, 14,
2253–2256.
6. (a) Marchand-Brynaert, J.; Dive, G.; Galleni, M.; Gerard, S. Bioorg. Med. Chem. 2004,
12, 129–138; (b) Firestone, R. A.; Barker, P. L.; Pisano, J. M.; Ashe, B. M.; Dahlgren,
M. E. Tetrahedron 1990, 46, 2255–2262.
7. Sutton, J. C.; Bolton, S. A.; Harti, K. S.; Huang, M. H.; Jacobs, G.; Meng, W.; Zhao, G.;
Bisacchi, G. S. Bioorg. Med. Chem. Lett. 2004, 14, 2233–2239.
8. Bode, W.; Meyer Jr., E.; Powers, J. C. Biochemistry 1989, 28, 1951–1963.
9. Tozser, J.; Sperka, T.; Pitlik, J.; Bagossi, P. Bioorg. Med. Chem. Lett. 2005, 15, 3086–3090.
10. Setti, E. L.; Davis, D.; Janc, J. M.; Jeffery, D. A.; Cheung, H.; Yu, W. Bioorg. Med. Chem.
Lett. 2005, 15, 1529–1534.
11. (a) Chen, D.; Falsetti, S. C.; Frezza, M.; Milacic, V.; Kazi, A.; Cui, Q. C.; Long, T. E.;
Turos, E.; Ping Dou, Q. Cancer Lett. 2008, 268, 63–69; (b) Banik, B. K.; Banik, I.; Becker,
F. F. Bioorg. Med. Chem. 2005, 13, 3611–3622.
12. O’Driscoll, M.; Greenhalgh, K.; Young, A.; Turos, E.; Dickey, S.; Lim, D. V. Bioorg.
Med. Chem. 2008, 16, 7832–7837.
13. Nivsarkar, M.; Thavaselvam, D.; Prasanna, S.; Sharma, M.; Kaushik, M. P. Bioorg. Med.
Chem. Lett. 2005, 15, 1371–1373.
14. Zoidis, G.; Fytas, C.; Papanastasiou, I.; Foscolos, G. B.; Fytas, G.; Padalko, E.; De Clercq,
E.; Naesens, L.; Neyts, J.; Kolocouris, N. Bioorg. Med. Chem. 2006, 14, 3341–3348.
15. Goel, R. K.; Mahajan, M. P.; Kulkarni, S. K. J. Pharm. Pharmaceut. Sci. 2004, 7, 80–83.
16. Goel, R. K.; Singh, A.; Naidu, P. S.; Mahajan, M. P.; Kulkarni, S. K. J. Pharm. Pharma-
ceut. Sci. 2005, 8, 182–189.
17. Ji, H.-F.; Shen, L.; Zhang, H.-Y. Biochem. Biophys. Res. Commun. 2005, 333, 661–663.
18. Carr, M.; Greene, L. M.; Knox, A. J. S.; Lloyd, D. G.; Zisterer, D. M.; Meegan, M. J.
Eur. J. Med. Chem. 2010, 45, 5752–5766.
19. (a) Okuyama, K.-I.; Momoi, Y.; Sugimoto, K.; Okano, K.; Tokuyama, H. Synlett 2011,
73–76; For a review, see (b) Alcaide, B.; Almendros, P.; Aragoncillo, C. Chem. Rev. 2007,
107, 4437–4492; (c) Palomo, C.; Oiarbide, M. in Topics in Heterocyclic Chemistry; B. K.
Banik (Ed.); Springer-Verlag: Berlin, 2010; Vol. 22, pp. 211–259; (d) Suffness, M. Taxol
Science and Applications; CRC Press: Boca Raton, FL, 1995.
20. (a) Alcaide, B.; Almendros, P. Progress in Heterocyclic Chemistry 2011, 22, 85–107; (b)
Singh, G. S.; D’hooghe, M.; De Kimpe, N. Tetrahedron 2011, 67, 1989–2012; (c) Georg,
G. I. The Organic Chemistry of b-Lactams; Verlag Chemie: New York, 1993.
21. Staudinger, H. Liebigs Ann. Chem. 1907, 356, 51–123.

734
M. ZAREI, Z. KARIMI-JABERI, AND A. MOVAHEDI
22. (a) Fodor, L.; Csomos, P.; Holczbauer, T.; Kalman, A.; Csampai, A.; Sohar, P.
Tetrahedron Lett. 2011, 52, 224–227; (b) Keri, R. S.; Hosamani, K. M.; Shingalapur,
R. V.; Reddy, H. R. S. Eur. J. Med. Chem. 2009, 44, 5123–5130; (c) Keri, R. S.; Hosamani,
K. M. Monatsh. Chem. 2010, 141, 883–888; (d) Jarrahpour, A.; Motamedifar, M.; Zarei,
M.; Mimouni, M. Phosphorusm, Sulfur Silicon Relat. Elem. 2010, 185, 287–297; (e)
Jarrahpour, A.; Zarei, M. Molecules 2006, 11, 49–58; (f) Jarrahpour, A.; Khalili, D.
Tetrahedron Lett. 2007, 48, 7140–7143; (g) Jarrahpour, A.; Ebrahimi, E. Molecules
2010, 15, 515–531.
23. (a) Qi, H.; Yang, Z.; Xu, J. Synthesis 2011, 723–730; (b) Tidwell, T. T. Ketenes II; John
Wiley & Sons: Hoboken, NJ, 2006, pp. 55–192.
24. (a) Jarrahpour, A.; Zarei, M. Tetrahedron 2010, 66, 5017–5023; (b) Jarrahpour, A.; Zarei,
M. Tetrahedron Lett. 2009, 50, 1568–1570; (c) Jarrahpour, A.; Zarei, M. Tetrahedron
2009, 65, 2927–2934; (d) Bose, A. K.; Manhas, M. S.; Amin, S. G.; Kapur, J. C.; Kreder,
J.; Mukkavilli, L.; Ram, B.; Vincent, J. E. Tetrahedron Lett. 1979, 20, 2771–2774; (e) Bose,
A. K.; Kapur, J. C.; Sharma, S. D.; Manhas, M. S. Tetrahedron Lett. 1973, 2319–2320; (f)
Jarrahpour, A.; Zarei, M. Molecules 2007, 12, 2364–2379; (g) Sharma, S. D.; Kanwar, S.
Org. Process Res. Dev. 2004, 8, 658–659; (h) Jarrahpour, A.; Zarei, M. Tetrahedron Lett.
2007, 48, 8712–8714; (i) Bhalla, A.; Nagpal, Y.; Kumar, R.; Mehta, S. K.; Bhasin, K. K.;
Bari, S. S. J. Organomet. Chem. 2009, 694, 179–189; (j) Meshram, J.; Ali, P.; Tiwari, V.
J. Heterocycl. Chem. 2010, 47, 1454–1458; (k) Jarrahpour, A.; Fadavi, A.; Zarei, M. Bull.
Chem. Soc. Jpn. 2011, 84, 320–327.
25. (a) Banfi, L.; Guanti, G.; Basso, A. Eur. J. Org. Chem. 2000, 939–946; (b) Nefzi, A.;
Giulianotti, M. A.; Ong, N. A.; Houghten, R. A. Org. Lett. 2000, 2, 3349–3350; (c)
Lee, J.; Gauthier, D.; Rivero, R. A. Tetrahedron Lett. 1998, 39, 201–204; (d) Georg, G.
I.; Kant, J. J. Org. Chem. 1988, 53, 692–695.
26. Layer, R. W. Chem. Rev. 1962, 62, 489–510, and references cited therein.
27. Billman, J. H.; Harting, W. F. J. Am. Chem. Soc. 1948, 70, 1473–1474.