Chemoselective reduction and transesterification of α-keto propargylic esters mediated by NaBH4 and CeCl37H 2O

Article abstract of DOI:10.1080/00397911.2010.502993

An efficient one-pot synthesis of α-hydroxy propargylic esters by chemoselective reduction followed by transesterification using NaBH₄ in combination with CeCl₃7H₂O is described.

Full text of DOI:10.1080/00397911.2010.502993

This article was downloaded by: [North Carolina State University]
On: 16 June 2013, At: 07:01
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
Chemoselective Reduction and
Transesterification of α-Keto Propargylic
Esters Mediated by NaBH4 and
CeCl3 · 7H2O
Thangavel Saravanan a & Anju Chadha a b
a Department of Biotechnology, Laboratory of Bioorganic Chemistry,
Indian Institute of Technology Madras, Chennai, India
b National Centre for Catalysis Research, Indian Institute of
Technology Madras, Chennai, India
Published online: 14 Jun 2011.
To cite this article: Thangavel Saravanan & Anju Chadha (2011): Chemoselective Reduction and
Transesterification of α-Keto Propargylic Esters Mediated by NaBH4 and CeCl3 · 7H2O, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:16, 2350-2358
To link to this article: http://dx.doi.org/10.1080/00397911.2010.502993
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, 41: 2350–2358, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.502993
CHEMOSELECTIVE REDUCTION AND
TRANSESTERIFICATION OF a-KETO PROPARGYLIC
ESTERS MEDIATED BY NaBH4 and CeCl3 ꢀ 7H2O
Thangavel Saravanan1 and Anju Chadha1,2
1Department of Biotechnology, Laboratory of Bioorganic Chemistry, Indian
Institute of Technology Madras, Chennai, India
2National Centre for Catalysis Research, Indian Institute of Technology
Madras, Chennai, India
GRAPHICAL ABSTRACT
Abstract An efficient one-pot synthesis of a -hydroxy propargylic esters by chemoselective
reduction followed by transesterification using NaBH4 in combination with CeCl3 ꢀ 7H2O is
described.
Keywords NaBH4=CeCl3.7H2O; reduction; transesterification
INTRODUCTION
Propargylic alcohols and esters are versatile building blocks as they allow for
facile conversion to a variety of functional groups in the synthesis of allenes, lac-
tones, and heterocycles, which are part of biologically active molecules[1] such as
thrombin receptor antagonists[2] and reverse transcriptase inhibitors.[3] These key
intermediates can be obtained by various chemical methods, which include direct
coupling reaction[4] or coupling followed by reduction.[5] Selective 1,2-reduction of
conjugated aldehydes and ketones by NaBH4=CeCl3 ꢀ 7H2O are known.[6] Because
of its unique catalytic properties (i.e., inexpensive, nontoxic, and water tolerant),
catalyst CeCl3 ꢀ 7H2O was used as a potential Lewis acid which imparts high region-
and chemoselectivity[7] in organic transformations such as hydro oxacyclization of
unsaturated 3-hydroxy esters,[8] Michael addition,[9] esterification of phenolic
alcohols,[10] enamination of b-dicarbonyl compounds,[11] allylation of aldehydes,[12]
Received February 22, 2010.
Address correspondence to Anju Chadha, Laboratory of Bioorganic Chemistry, Department of
Biotechnology, Indian Institute of Technology Madras, Chennai 600036, India. E-mail: anjuc@iitm.ac.in
2350

CHEMOSELECTIVE REDUCTION AND TRANSESTERIFICATION
2351
Scheme 1. Reduction cum transesterification of a-keto propargylic esters using NaBH4=CeCl3 ꢀ 7H2O.
dihydroxylation of unreactive olefins,[13] and Julia olefination of cyclopropyl
carbinols,[14] synthesis of N,N-disubtituted ureas,[15] and quinoline derivatives.[16]
Recently, Meng et al. developed the Ru-catalyzed enantioselective hydrogenation
of aromatic a-ketoesters with CeCl3 ꢀ 7H2O as an effective additive.[17] To prepare
racemic a-hydroxy propargylic esters as substrates[18] for Candida parapsilosis ATCC
7330, which is known to efficiently catalyze deracemization,[19] we followed the
reported procedure[5] using NaBH4=CeCl3 ꢀ 7H2O. Significantly, in addition to
reduction, a transesterfied product was formed; that is, reduction of methyl
2-oxo-phenylbut-3-ynoate in ethanol with NaBH4=CeCl3 ꢀ 7H2O resulted in the for-
mation of ethyl 2-hydroxy-4-phenylbut-3-ynoate. This interesting result prompted us
to study the importance of NaBH4=CeCl3 ꢀ 7H2O as a reducing cum transesterifiying
agent for various a-keto propargylic esters.
Esters are generally synthesized either from reaction of carboxylic acid with
alcohol[20] and=or by transesterification of an ester with an alcohol.[21] Poor solu-
bility of some acids in organic solvents makes transesterification more advantageous
than ester synthesis.[22] Transesterification is an important reaction as it used to pre-
pare organic intermediates in the synthesis of biologically important molecules and
also in the preparation of biodiesel.[21a,23] Thus, a number of useful procedures cat-
alyzed by a variety of protic and Lewis acids,[22,24] organic and inorganic bases,[25]
enzymes and antibodies[21c,26] have been developed for transesterification. However,
methods for the transesterification of a-keto esters[27] are rather few. Despite the
numerous methods of transesterification reported in literature, there is a constant
need to develop new protocols that require mild conditions, especially for com-
pounds with acid- and base-sensitive functionalities such as hydroxy, ester, and
alkyne moieties. To the best of our knowledge, there has been no report on transes-
terification of a-keto propargylic esters using NaBH4=CeCl3 ꢀ 7H2O. Earlier work
from our laboratory reported the reduction cum transesterification of b-keto esters
using NaBH4.[28] Herein, we report an efficient one-pot reaction to obtain different
types of a-hydroxy propargylic esters from a -keto propargylic esters by using
NaBH4=CeCl3 ꢀ 7H2O in different alcohols at room temperature under mild reaction
conditions (Scheme 1).
RESULTS AND DISCUSSION
In a typical experiment, a-keto propargylic esters were treated with the desired
alcohols, and the corresponding reduced cum transesterfied products were obtained
in moderate to good yields. The results are summarized in Table 1. In optimization
studies, we tried the reaction with various concentration of NaBH4 for methyl

2352
T. SARAVANAN AND A. CHADHA
Table 1. Reduction cum transesterification of a-keto propargylic esters using NaBH4=CeCl3 ꢀ 7H2O
a
Entry
1
Solvent
Product
Time (h)
3
Isolated yield (%)
71
CH3
CH3CH2OH
2
3
CH3
CH3
6
6
65
67
4
5
6
CH3
CH3
CH3
12
12
12
61
58
51
7
8
9
CH3CH2
CH3CH2
CH3CH2
CH3OH
3
6
69
62
63
12
10
11
12
CH3CH2
CH3CH2
CH3CH2
24
12
12
20
41
37
aMethyl 4-phenyl-2-oxobut-3-ynoate and ethyl 4-phenyl-2-oxobut-3-ynoate were synthesized according
to the literature report.[5]
2-oxo-4-phenylbut-3-ynoate in ethanol (with 1.2 equiv. of CeCl3 ꢀ 7H2O in 3 h reac-
tion time). The yields obtained for 0.25, 0.5, 0.75, and 1.0 equiv. of NaBH4 were
53%, 71%, 61%, and 42% respectively. The reaction was not complete with 0.25

CHEMOSELECTIVE REDUCTION AND TRANSESTERIFICATION
2353
Scheme 2. Reduction cum transesterification of methyl 2-oxo-4-phenylbut-3-ynoate using NaBH4/
CeCl3 ꢀ 7H2O.
equiv., and 38% of starting material was recovered. With 0.75 and 1.0 equiv. of
NaBH4, the corresponding diol product was also observed in 17% and 39% yields
respectively because of the reduction of both keto and ester groups (Scheme 2). With
0.5 equiv., a maximum yield of 71% was observed because of the selective reduction
of the keto group. On the basis of these results, all the experiments were done with
0.5 equiv. of NaBH4.
According to these optimized reaction conditions, methyl 2-oxo-4-phenylbut-
3-ynoate on treatment with ethanol in the presence of NaBH4=CeCl3 ꢀ 7H2O led to
the corresponding reduced cum transesterfied product with 71% yield in 3 h due to
the good solubility of catalyst (entry 1). Furthermore, methyl 2-oxo-4-phenylbut-
3-ynoate with n-propanol, n-butanol, and iso-propanol gave the corresponding
transesterfied hydroxy (reduced) products with yields ranging from 61 to 67%
(entries 2–4). In the presence of allyl and propargyl alcohols, the formation of the
corresponding products, allyl 2-hydroxy-4-phenylbut-3-ynoate, and prop-2-ynyl
2-hydroxy-4-phenylbut-3-ynoate in 58% and 51% yield respectively (entries 5 and
6) were observed. These two compounds are reported here for the first time.
Ethyl 2-oxo-4-phenylbut-3-ynoate with methanol, n-propanol, and n-butanol
led to the formation of corresponding transesterfied reduced products in 62–69%
yields (entries 7–9) while with allyl and propargyl alcohols, the transesterfied reduced
products were isolated in 41% and 37% yields respectively (entries 11 and 12). With
iso-propanol, the reduction was completed within 15 min, but the transesterfied pro-
duct was obtained only after 24 h in 20% yield (entry 10). Use of tert-butanol,
2-methoxyethonol, and benzyl alcohol with methyl and ethyl 2-oxo-4-phenylbut-
3-ynoate did not give the desired transesterfied product even after 24 h, possibly
because of the poor solubility of the catalyst but the reduced untransesterfied
product formed within 30 min.
To ensure that CeCl3 ꢀ 7H2O facilitated the transesterification process, the reac-
tion (entry 1) was carried out in the absence of CeCl3 ꢀ 7H2O. The reaction did not
proceed even after 24 h. On the other hand, the same reaction in the absence of
NaBH4, after 24 h reaction time, gave only 18% of the transesterfied product without
reduction. The results of these experiments confirmed that both NaBH4 and
CeCl3 ꢀ 7H2O are necessary for the reduction cum transesterification reaction.
Mechanistically, NaBH4 alone acts as a soft reducing agent, and the active spe-
cies during the Luche reduction was believed to be an alkoxy borohydride, which in
combination with the hard Ce3þ cation acts as a hard reducing agent.[6c,29] The cerium
plays an important role as catalyst in the formation of alkoxy borohydrides and
increases the electrophilicity of the carbonyl carbon atom.[6c,29] From a mechanistic

2354
T. SARAVANAN AND A. CHADHA
Scheme 3. Plausible mechanism.
standpoint, cerium ions preferentially coordinate to the oxygen atom of solvent and
increase the acidity of the medium,[30] thus helping to activate the carbonyl carbon
of the ketone in the reduction and also activating the carbonyl carbon of the ester
in the transesterification (Scheme 3).
CONCLUSIONS
In conclusion, we have developed a highly efficient method for the chemoselec-
tive reduction and transesterification for a -keto propargylic esters mediated by
NaBH4=CeCl3 ꢀ 7H2O. The notable advantages of the procedure are (a) simple and
one-pot reaction, (b) easy availability and nontoxic nature of the reagent, (c) mild
reaction conditions (tolerance to sensitive functionalities such as hydroxy, ester,
and alkyne moieties during transesterification), (d) the solvents need not to be dried,
(e) CeCl3 can be used directly as its heptahydrate and no drying is needed, and (f)
neither inert atmosphere not the protection of hydroxy group is required.
EXPERIMENTAL
1H and 13C NMR spectra were recorded in CDCl3 solution on a Bruker
AV-400 spectrometer operating at 400 and 100 MHz, respectively. Chemical shifts
are expressed in parts per million (ppm) values using tetramethylsilane (TMS) as
an internal standard. TLC was carried out on Kieselger 60 F254 aluminium sheets
(Merck1.05554). All chemicals were obtained from Aldrich and Merck.
General Procedure for the Reduction Cum Transesterification
Reaction
The a-keto propargylic ester (2.50 mmol) was treated with the desired alcohol
(15 ml) in the presence of NaBH4 (1.25 mmol) and CeCl3 ꢀ 7H2O (3.13 mmol) at room
temperature. The reaction was monitored by TLC, and after completion, excess alco-
hol was stripped off. The reaction mixture was quenched with dilute HCl and
extracted with dechloremethane (DCM). The organic layer was dried, concentrated,
purified by silica-gel column chromatography, and characterized by infrared (IR),
1H and 13C NMR, and high-resolution mass spectrometry (HRMS).

CHEMOSELECTIVE REDUCTION AND TRANSESTERIFICATION
2355
Some Selected Spectral Data of the Products
Allyl 2-Hydroxy-4-phenylbut-3-ynoate (entries 5 and 11). 1H NMR
(400 MHz, CDCl3): d ¼ 3.16 (1H, d, J ¼ 7.2 Hz), 4.78 (2H, m), 5.10 (1H, d,
J ¼ 7.2 Hz), 5.30 (1H, dd, J ¼ 10.4 Hz & 1.6 Hz), 5.41 (1H, dd, J ¼ 17.2 Hz &
1.6 Hz), 5.96 (1H, m), 7.31–7.33 (3H, m), 7.44–7.46 (2H, m). 13C NMR (100 MHz,
CDCl3) : d 170.0, 131.9, 131.0, 128.9, 128.3, 121.7, 119.1, 85.6, 84.1, 67.0, 61.9. IR
(n, cmꢁ1): 3451, 2926, 2155, 1742, 1602, 1489, 1445, 1263, 1197, 1079, 756. HRMS:
m=z, calcd. Mass: 239.0684 [(M þNa)þ]; found: 239.0689 [(M þNa)þ].
Prop-2-ynyl 2-Hydroxy-4-phenylbut-3-ynoate (entries 6 and 12). 1H
NMR (400 MHz, CDCl3): d ¼ 2.55 (1H, t, J ¼ 2 Hz), 3.08 (1H, d, J ¼ 7.6 Hz), 4.87
(2H, dq, J ¼ 15.2 Hz & 2 Hz), 5.12 (1H, d, J ¼ 7.6 Hz), 7.29–7.36 (3H, m),
7.45–7.47 (2H, m). 13C NMR (100 MHz, CDCl3): d 169.6, 132.1, 129.1, 128.4,
121.7, 86.2, 83.6, 76.5, 76.1, 62.1, 54.0 IR (n, cmꢁ1): 3417, 3290, 2955, 2233, 2188,
2164, 1754, 1441, 1192, 1082, 994, 761. HRMS: m=z, calcd. Mass: 237.0528 [(M
þNa)þ], found: 237.0515 [(M þNa)þ].
ACKNOWLEDGMENTS
One of the authors (Thangavel Saravanan) thanks Indian Institute of
Technology (IIT) Madras and the University Grants Commission, India, for the
fellowship. We thank the Sophisticated Analytical Instrumentation Facility (SAIF)
and Department of Chemistry, IIT Madras, for NMR and mass analysis.
REFERENCES
1. (a) Stang, P. J.; Diederich, F. (Eds.). Modern Acetylene Chemistry; VCH: Weinheim,
Germany, 1995; (b) Shi Shun, A. L. K.; Tykwinski, R. R. Synthesis of naturally occuring
polyynes. Angew. Chem. Int. Ed. 2006, 45, 1034–1057.
2. Li, T.; Tamaraz, M. M.; Zaks, A. Preparation of chiral propargylic alcohol and ester
intermediates of himbacine analogs. PCT Int. Appl. WO patent 2006076565, 2006.
3. Trost, B. M.; Weiss, A. H. Catalytic enantioselective synthesis of adociacetylene B. Org.
Lett. 2006, 8, 4461–4464.
4. Meyer, A.; Flammang, M.; Wermuth, C. G. Synthesis of 3-unsubstituted 2-hydroxy-
4-oxoalkanoates. Synthesis 1976, 832–832.
5. (a) Guo, M.; Li, D.; Zhang, Z. Novel synthesis of 2-oxo-3-butynoates by copper-catalyzed
cross-coupling reaction of terminal alkynes and monooxalyl chloride. J. Org. Chem. 2003,
68, 10172–10174; (b) Tanaka, K.; Shoji, T.; Hirano, M. Cationic rhodium (I)=bisphos-
phane complex-catalyzed isomerization of secondary propargylic alcohols to a,b-enones.
Eur. J. Org. Chem. 2007, 2687–2699.
6. (a) Luche, J. L. Lanthanides in organic chemistry, 1: Selective 1,2-reductions of conjugated
ketones. J. Am. Chem. Soc. 1978, 100, 2226–2227; (b) Luche, J. L.; Rodriguez-Hahn, L.;
Crabbe, P. Reduction of natural enones in presence of cerium trichloride. J. Chem. Soc.,
Chem. Commun. 1978, 601–602; (c) Gemal, A. L.; Luche, J. L. Lanthanoids in organic syn-
thesis, 6: The reduction of a-enones by sodium borohydride in the presence of lanthanoid
chlorides: Synthetic and mechanistic aspects. J. Am. Chem. Soc. 1981, 103, 5454–5459.
7. (a) Bartoli, G.; Marcantoni, E.; Sambri, L. The CeCl3 ꢀ nH2O=NaI system in organic
synthesis: An efficient water-tolerant Lewis acid promoter. Synlett 2003, 2101–2106;

2356
T. SARAVANAN AND A. CHADHA
(b) Yadav, J. S.; Reddy, B. V. S.; Rao, C. V.; Chand, P. K.; Prasad, A. R. A facile and
selective cleavage of prenyl esters catalyzed by CeCl3 ꢀ 7 H2O-NaI. Synlett 2002, 137–
139; (c) Yadav, J. S.; Reddy, B. V. S.; Reddy, M. S.; Sabitha, G. A facile cleavage of
ketone N,N-dimethylhydrazones by CeCl3 ꢀ 7H2O-SiO2.. Synlett 2001, 1134–1136; (d)
Deo, D. M.; Marcantoni, E.; Torregiani, E. A simple, efficient, and general method for
the conversion of alcohols into alkyl iodides by a CeCl3 ꢀ 7H2O=NaI system in acetonitrile.
J. Org. Chem. 2000, 65, 2830–2833.
8. Marotta, E.; Foresti, E.; Marcelli, T.; Peri, F.; Righi, P.; Scardovi, N.; Rosini, G.
CeCl3 ꢀ 7H2O-NaI-catalyzed hydrooxocyclization of unsaturated 3-hydroxy esters. Org.
Lett. 2002, 4, 4451–4453.
9. (a) Boruah, A.; Baruah, M.; Prajapati, D.; Sandhu, J. S. Cerium-catalyzed Michael
addition of 1,3-dicarbonyl compounds under microwave irradiation. Synth. Commun.
1998, 28, 653–658; (b) Bartoli, G.; Bartolacci, M.; Giuliani, A.; Marcantoni, E.;
Massaccesi, M.; Torregiani, E. Improved heteroatom nucleophilic addition to
electron-poor alkenes promoted by CeCl3 ꢀ 7H2O=NaI system supported on alumina in
solvent-free conditions. J. Org. Chem. 2005, 70, 169–174.
10. Torregiani, E.; Seu, G.; Minassic, A.; Appendino, G. Cerium(III) chloride–promoted che-
moselective esterification of phenolic alcohols. Tetrahedron Lett. 2005, 46, 2193–2196.
11. Khodaei, M. M.; Khosropout, A. R.; Kookhazadeh, M. Enamination of b-dicarbonyl
compounds catalyzed by CeCl3 ꢀ 7H2O at ambient conditions: ionic liquids and
solvent-free media. Synlett 2004, 11, 1980–1984.
12. Bartoli, G.; Giuliani, A.; Marcantoni, E.; Massaccesi, M.; Melchiorre, P.; Lanari, S.;
Sambri, L. Allylation of aldehydes promoted by the cerium(III) chloride heptahydrate=
sodium iodide system: The dependence of regio- and stereocontrol on the reaction
conditions. Adv. Synth. Catal. 2005, 347, 1673–1680.
13. Plietker, B.; Niggemann, M. RuCl3=CeCl3=NaIO4: A new bimetallic oxidation system
for the mild and efficient dihydroxylation of unreactive olefins. J. Org. Chem. 2005, 70,
2402–2405.
14. Li, W. D. Z.; Peng, Y. An effective and highly stereoselective julia olefination of cyclo-
propyl carbinol mediated by CeCl3 ꢀ 7H2O=NaI. Org. Lett. 2005, 7, 3069–3072.
15. Li, Z.; Wang, Z. Y.; Zhu, W.; Xing, Y. L.; Zhao, Y. L. CeCl3 ꢀ 7H2O-KI catalysed envir-
ontmentally friendly synthesis of N,N-disubstituted ureas in water under microwave
irradiation. Synth. Commun. 2005, 35, 2325–2331.
16. (a) Bose, D. S.; Kumar, R. K. An efficient, high-yielding protocol for the synthesis of
functionalized quinolines via tandem addition=annulation reaction of o-aminoaryl
ketones with a -methylene ketones. Tetrahedron Lett. 2006, 47, 813–816; (b) Jia, C. S.;
Dong, Y. W.; Tu, S. J.; Wang, G. W. Microwave-assisted solvent-free synthesis of substi-
tuted 2-quinolones. Tetrahedron 2007, 63, 892–897; (c) Yadav, J. S.; Reddy, B. V. S.;
Sathaiah, K.; Vishnumurthy, P. First example of functionalization of activated quinolines
by indoles using CeCl3 ꢀ 7H2O. Synlett 2005, 18, 2811–2813.
17. Meng, Q.; Sun, Y.; Ratovelomanana-Vidal, V.; Genet, J. P.; Zhang, Z. CeCl3 ꢀ 7H2O:
An effective additive in Ru-catalyzed enantioselective hydrogenation of aromatic a-ketoe-
sters. J. Org. Chem. 2008, 73, 3842–3847.
18. Saravanan, T.; Chadha, A. Biocatalytic deracemization of alkyl-2-hydroxy-4-arylbut-3-
ynoates using whole cells of Candida parapsilosis ATCC 7330. Tetrahedron: Asymmetry
2010, 21, 2973–2980.
19. Chadha, A.; Baskar, B. Biocatalytic deracemisation of a-hydroxy esters: High yield prep-
aration of (S)-ethyl 2-hydroxy-4-phenylbutanoate from the racemate. Tetrahedron: Asym-
metry 2002, 13, 1461–1464; (b) Baskar, B.; Pandian, N. G.; Priya, K.; Chadha, A.
Deracemisation of aryl substituted a-hydroxy esters using Candida parapsilosis ATCC
7330: Effect of substrate structure and mechanism. Tetrahedron 2005, 61, 12296–12306;

CHEMOSELECTIVE REDUCTION AND TRANSESTERIFICATION
2357
(c) Padhi, S. K.; Chadha, A. Deracemisation of aromatic b-hydroxy esters using immobi-
lised whole cells of Candida parapsilosis ATCC 7330 and determination of absolute
configuration by 1H NMR. Tetrahedron: Asymmetry 2005, 16, 2790–2798; (d) Thangavel,
V.; Chadha, A. Preparation of optically pure (3E,5E)-alkyl-2-hydroxy-6-
arylhexa-3,5-dienoates by Candida parapsilosis ATCC 7330–mediated deracemization of
the racemates. Tetrahedron 2007, 63, 4126–4133; (e) Titu, D.; Chadha, A. Enantiomeri-
cally pure allylic alcohols: Preparation by Candida parapsilosis ATCC 7330–mediated
deracemization. Tetrahedron: Asymmetry 2008, 19(14), 1698–1701.
20. (a) Larock, R. C. In Comprehensive Organic Transformation; Wiley-VCH: New York,
1999; (b) Smith, M. B.; March, J. In Advanced Organic Chemistry, 5th ed.; Wiley: New
York, 2001; (c) Dhimitruka, L.; SantaLucia, J. Jr. Investigation of the Yamaguchi esteri-
fication mechanism: Synthesis of a Lux-S enzyme inhibitor using an improved esterificaion
method. Org. Lett. 2006, 8, 47–50.
21. (a) Green, T. W.; Wuts, P. G. M. In Protective Groups in Organic Synthesis, 3rd ed.; Wiley:
New York, 1999; (b) Otera, J. Transesterification. Chem. Rev. 1993, 93, 1449–1470, and
references cited therein; (c) Guieysse, D.; Salagnad, C.; Monsan, P.; Remaud-Simeon,
M. Lipase-catalyzed enantioselective transesterification toward ester of 2-bromo-
tolylacetic acids. Tetrahedron: Asymmetry 2003, 14, 317–323; (d) Chavan, S. P.;
Shivasankar, K.; Sivappa, R.; Kale, R. Zinc-mediated transesterification of b-ketoesters
and coumarin synthesis. Tetrahedron Lett. 2002, 43, 8583–8586.
22. Palaniappan, S.; Chandra Shekhar, R. Transesterification of ketoesters with alcohols
using polyaniline salts as catalysts. Polym. Adv. Technol. 2004, 15, 140–143.
23. (a) Solhy, A.; Clark, J. H.; Tahir, R.; Sebti, S.; Larzek, M. Transesterification catalyzed by
solid, reusable apatite-zinc chloride catalysts. Green Chem. 2006, 8, 871–874; (b) Ghesti,
G. F.; Macedo, J. L.; Parente, V. C. I.; Dias, J. A.; Dias, S. C. L. Synthesis, characteriza-
tion, and reactivity of Lewis acid=surfactant cerium trisdodecylsulfate catalyst for
transesterification and esterification reactions. Appl. Catal. A: Gen. 2009, 355, 139–147.
24. (a) Ramalinga, K.; Vijayalakshmi, P.; Kaimal, T. N. B. A mild and efficient method for
esterification and transesterification catalyzed by iodine. Tetrahedron Lett. 2002, 43, 879–
882; (b) Shapiro, G.; Marzi, M. Facile and selective O-alkyl transesterification of primary
carbamates with titanium(IV) alkoxides. J. Org. Chem. 1997, 62, 7096–7097; (c) Rethberg,
C. E.; Fisher, C. H. Preparation and properties of the n-alkyl acrylates. J. Am. Chem. Soc.
1944, 66, 1203–1207; (d) Holmquist, C. R.; Roskamp, E. J. A selective method for diace-
tate catalysed the direct conversion of aldehyde into b-keto esters with ethyl diazoacetate
catalyzed by tin(II) chloride. J. Org. Chem. 1989, 54, 3258–3260; (e) Ranu, B. C.; Dutta,
P.; Sarkar, A. A simple and efficient procedure for transesterification catalyzed by indium
triiodide. J. Org. Chem. 1998, 63, 6027–6028; (f) Ponde, D. E.; Deshpande, V. H.; Bulbule,
V. J.; Sudalai, A.; Gajare, A. S. Selective catalytic transesterification, transthiolesterifica-
tion, and protection of carbonyl compounds over natural kaolinitic clay. J. Org. Chem.
1998, 63, 1058–1063; (g) Madje, B. R.; Patil, P. T.; Shindalkar, S. S.; Benjamin, S. B.;
Shingare, M. S.; Dongare, M. K. Facile transesterification of b-ketoesters under
solvent-free condition using borate zirconia solid acid catalyst. Catal. Commun. 2004, 5,
353–357.
25. (a) Suarez-Castillo, O. R.; Montiel-Ortega, L. A.; Fragoso-Vazquez, M. J.; Melendez-
Rodriguez, M.; Sanchez-Zavala, M. Transesterifications mediated by t-BuNH2. Tetra-
hedron Lett. 2008, 49, 996–999, and references cited therein; (b) Meth-Cohn, O. A simple,
powerful, and efficient method for transesterification. J. Chem. Soc., Chem. Commun.
1986, 695–697; (c) Billman, J. H.; Smith, W. T. Jr.; Rendall, J. L. Anticonvulsants, V:
Esters of c-diethylamino-a-phenylbutyric acid. J. Am. Chem. Soc. 1947, 69, 2058–2059;
(d) Choudary, B. M.; Kantam, M. L.; Reddy, C. V.; Aranganathan, S.; Santhi, P. L.;
Figueras, F. Mg–Al–O–t-Bu hydrotalcite: A new and efficient heterogeneous catalyst

2358
T. SARAVANAN AND A. CHADHA
for trans-esterification. J. Mol. Catal. A: Chem. 2000, 159, 411–416; (e) Balaji, B. S.;
Chanda, B. M. Simple and high-yielding syntheses of b-keto esters catalysed by zeolites.
Tetrahedron 1998, 54, 13237–13252; (f) Ilankumaran, P.; Verkade, J. G.
P(RNCH2CH2)3N: Efficient catalysts for transesterifications, acylations, and deacyla-
tions. J. Org. Chem. 1999, 64, 3086–3089.
26. (a) Fernholz, E.; Schloeder, D.; Liu, K. K. C.; Bradshaw, C. W.; Haung, H.; Janda, K.;
Lerner, R. A.; Wong, C. H. Specificity of antibody-catalysed transesterification using enol
esters: A comparision with lipase reactions. J. Org. Chem. 1992, 57, 4756–4761; (b) Priya,
K.; Chadha, A. Synthesis of hydrocinnamic esters by Pseudomonas cepacia lipase. Enzyme
Microb. Technol. 2003, 32, 485–490; (c) Vidya, P.; Chadha, A. The role of different anions
in ionic liquids on Pseudomonas cepacia lipase–catalyzed transesterification and hydroly-
sis. J. Mol. Catal. B: Enzymatic 2009, 57, 145–148; (d) Wirsching, P.; Ashley, J. A.;
Benkovic, S. J.; Janda, K. D.; Lerner, R. A. An unexpectedly efficient catalytic anitbody
operating by ping-pong and induced fit mechanism. Science 1991, 252, 680–685.
27. (a) Coskun, N.; Er, M. New alkoxyzinc salts–mediated chemoselective transesterification
reactions. Turk. J. Chem. 2005, 29, 455–461; (b) Yang, Y. H.; Shi, M. Lewis acid–
mediated reactions of cyclopropyl aryl ketones with a-ketoesters: Facile preparation of
5,6-dihydropyran-2-ones. J. Org. Chem. 2005, 70, 10082; (c) Yang, Y. H.; Shi, M. A
stereoselective synthetic route to 1,6-dioxaspiro[4.4]non-3-en-2-ones from cyclopropyl
alkyl ketones and a-ketoesters. Org. Lett. 2006, 8, 1709–1712.
28. Padhi, S. K.; Chadha, A. Sodium borohydride reduction and selective transesterification
of b-keto ester in a one-pot reaction under mild conditions. Synlett 2003, 639.
29. (a) Lefour, J. M.; Loupy, A. The effect of cations on nucleophilic additions to carbonyl
compounds: carbonyl complexation control versus ionic association control. Application
to the regioselectivity of addition of a-enones. Tetrahedron 1978, 34, 2597–2605; (b)
Ohwada, T. Orbital-controlled stereoselections in sterically unbiased cyclic system. Chem.
Rev. 1999, 99, 1337–1375.
30. Cockerill, A. F.; Davies, G. L. O.; Harden, R. C.; Rackham, D. M. Lanthanide shift
reagents for nuclear magnetic resonance spectroscopy. Chem. Rev. 1973, 73, 553–588.