Catalytic oxidative esterification of aldehydes and alcohols using KI-TBHP

Article abstract of DOI:10.1080/00397910902838920

A simple and mild procedure for the facile oxidative esterification of aldehydes and alcohols using potassium iodide (KI) in combinzation with tert-butyl hydroperoxide (TBHP) as an external oxidant is described. Oxidative esterification is induced by iodine generated in situ by the chemical oxidation of KI with TBHP.

Full text of DOI:10.1080/00397910902838920

This article was downloaded by: [University of Stellenbosch]
On: 04 May 2013, At: 10:52
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
Catalytic Oxidative Esterification of
Aldehydes and Alcohols Using KI–TBHP
K. Rajender Reddy a , M. Venkateshwar a , C. Uma Maheswari a & S.
Prashanthi a
a Inorganic and Physical Chemistry Division, Indian Institute of
Chemical Technology, Tarnaka, Hyderabad, India
Published online: 29 Dec 2009.
To cite this article: K. Rajender Reddy , M. Venkateshwar , C. Uma Maheswari & S. Prashanthi (2009):
Catalytic Oxidative Esterification of Aldehydes and Alcohols Using KI–TBHP, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 40:2, 186-195
To link to this article: http://dx.doi.org/10.1080/00397910902838920
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, 40: 186–195, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910902838920
CATALYTIC OXIDATIVE ESTERIFICATION OF ALDEHYDES
AND ALCOHOLS USING KI–TBHP
K. Rajender Reddy, M. Venkateshwar, C. Uma Maheswari, and
S. Prashanthi
Inorganic and Physical Chemistry Division, Indian Institute of Chemical
Technology, Tarnaka, Hyderabad, India
A simple and mild procedure for the facile oxidative esterification of aldehydes and alcohols
using potassium iodide (KI) in combinzation with tert-butyl hydroperoxide (TBHP) as an
external oxidant is described. Oxidative esterification is induced by iodine generated in situ
by the chemical oxidation of KI with TBHP.
Keywords: Alcohol; aldehydes; esterification; oxidation; potassium iodide
INTRODUCTION
The development of simple and convenient methods, which generate less waste
and avoid the use of toxic reagents, is an important strategy in an environmentally
conscious world.[1] Oxidations are an important class of reactions that have wide-
spread applications in synthetic organic chemistry.[2] Direct conversion of aldehyde
into ester is one such reaction often required in the synthesis of natural products.[3]
Traditional synthesis of esters generally involves the nucleophilic addition of an alco-
hol to activated carboxylic acid derivatives such as acid anhydrides or chlorides.[4]
Recently, several catalytic methods have been reported for the direct conversion of
aldehydes to esters using different catalysts and reagents, for example, MnO2–
hydrogen cyanide (HCN),[3a] bis(pyridine)iodonium tetrafluoroborate (Ipy2BF4),[5a]
N-iodosuccinimide (NIS),[5b] MTO (methyltrioxorhenium)–H2O2,[5c] oxone,[5d] V2O5–
sodium perborate (SPB) or SPC (sodium peroxide or sodium percarboate),[5e]
Cu(ClO4)2–InBr3–TBHP,[5f] Pd-siloxane,[5g] and NaIO4=LiBr.[5h] Unfortunately,
several of these methods have limitations in terms of cost, ready availability, and safe
and easy handling of the reagents and catalysts.
Molecular halogens and related reagents are well known for various oxidation
reactions because of their simple operation and low cost.[6] Among the several
reagents reported in the literature, molecular iodine is an attractive candidate
because it is cheap, readily available, and moreover less toxic than molecular
Received November 17, 2008.
Address correspondence to K. Rajender Reddy, Inorganic and Physical Chemistry Division, Indian
Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500607, India. E-mail: rajender@
iict.res.in, rajenderkallu@yahoo.com
186

CATALYTIC OXIDATIVE ESTERIFICATION
187
bromine or chlorine.[7] Several reports appeared recently on the use of iodine for
organic transformations, including the formation of heterocycles,[8] C–C bond
formation,[9] iodocyclization,[10] and in protection=deprotections.[11] Furthermore,
molecular iodine is efficiently utilized for oxidation of alcohols and aldehydes into
the corresponding esters.[12] One of the limitations of these procedures is the use
of a large excess of iodine and a base, which could lead to a large amount of waste.
To overcome some of the problems encountered in the earlier methods, we
were interested in developing a catalytic system based on in situ generated iodine
and a base. Recently we reported oxidative amidation of aldehydes with amines
using a catalytic amount of KI in the presence of TBHP as an external oxidant.[13]
Using a similar approach, an efficient and an environmentally friendly system was
developed for the selective oxidation of aldehydes to esters.
RESULTS AND DISCUSSION
In an effort to develop an optimal catalytic system, a systematic study was
carried out with KI using 4-nitrobenzaldehyde as a model substrate in the presence
of TBHP as an external oxidant (Table 1). The reaction was carried out by adding
TBHP to a solution of 4-nitrobenzaldehyde and KI in methanol at room tempera-
ture. The reaction was completed in 1 h when 5 equivalents each of KI and TBHP
were used (Table 1, entry 1), whereas no reaction was observed under the blank con-
ditions even at longer reaction times (Table 1, entries 2 and 3). Decreasing the KI to
a catalytic amount (20 mol%) led to the completion of the reaction after 10 h, and
under similar reaction conditions, the use of hydrogen peroxide as an oxidant pro-
vided only 6% conversion after 21 h. Further optimization led to the use of 5 mol%
of KI and 1.5 mmol of TBHP at elevated temperatures (65ꢀC). The NMR spectrum
at different intervals of time clearly shows the formation of ester exclusively (Fig. 1).
Table 1. Screening of reaction parameters for the synthesis of 1a
S. no.
KI (mmol)
Oxidant (mmol)
Time (h)
Conv. (%)a
Sel. (%)a
1
2
3
4
5
6
7
5
TBHP (5)
––
1
18
19
10
21
16
16
99
––
2
99
––
95
98
95
98
98b
5
––
TBHP (5)
TBHP (5)
H2O2 (5)
TBHP (1.5)
TBHP (1.5)
0.2
0.2
0.2
0.05
99
6
99
99b
aConversion and selectivity by 1H NMR.
bReaction carried out at 65ꢀC.

188
K. RAJENDER REDDY ET AL.
Figure 1. 1H NMR spectra for the esterification reaction with KI–TBHP at room temperature: (A) pure
p-nitrobenzaldehyde, (B) reaction mixture after 6 h, and (C) reaction mixture after 16 h (ꢁcorresponds to
the signals from the p-nitrobenzaldehyde).
With the optimized reaction conditions in hand, we examined the scope of the
KI–TBHP catalytic system for the oxidative esterification of different aldehydes with
methanol (Table 2). In general, the KI–TBHP-catalyzed oxidative esterification
occured smoothly to provide the desired ester in good yields. The oxidative esterifi-
cation reaction was amenable to both electron-rich and electron-poor aromatic
aldehydes (entries 1–8). Electron-withdrawing groups on the aromatic ring enhance
the activity. More gratifying was the compatibility of the reaction to proceed success-
fully with hetero-aromatic and aliphatic aldehydes as substrates (entries 10–14).
Further, we looked at the feasibility of this reaction with different alcohols
(Scheme 1). Reaction of 4-nitrobenzaldehyde (1 mmol) with propanol (10 mmol)
resulted in complete conversion of aldehyde to ester, and similarly the reaction of
4-nitrobenzaldehyde with benzyl alcohol (10 mmol) provided 70% of the correspond-
ing ester.
Encouraged by these results, we made an investigation on the possible conver-
sion of benzyl alcohols to the corresponding methyl esters, and the results are shown
in Table 3. Reaction with 5 mol% of the catalyst resulted in less conversion; however,
increasing the catalyst concentration to 20 mol% provided the products in reasonable
conversion. In general, good selectivity for ester was observed with electron-
withdrawing groups.
A catalytic cycle is shown in Scheme 2, where the TBHP oxidizes potassium
iodide to generate molecular iodine and potassium hydroxide as the initiating
species. It is known that molecular iodine under alkaline conditions generates esters
via hemiacetal.[12,14] To test the role of in situ generated iodine and base, two reac-
tions have been carried out. The reaction with iodine and potassium hydroxide
(KOH) resulted in complete conversion to ester as reported earlier,[14] whereas the
reaction of a catalytic amount of I2 (10 mol%) with TBHP yielded acetal as the major
product. These results clearly confirm that both in situ generated iodine and base are
essential for the formation of ester. In the case of alcohols, the reaction proceeds
through the formation of an aldehyde intermediate.

CATALYTIC OXIDATIVE ESTERIFICATION
189
Table 2. Oxidative esterification of aldehydes with methanol using KI–TBHPa
Entry
1
Substrate
Time (h)
Yield (%)b
10
97
2
3
4
5
6
7
16
14
12
17
17
18
90
98
96
83
78
78
8
20
69
9
10
11
20
18
19
60
81
75
12
20
74
(Continued )

190
K. RAJENDER REDDY ET AL.
Table 2. Continued
Entry
13
Substrate
Time (h)
Yield (%)b
20
74c
14
20
95c
aReaction conditions: aldehyde (1.0 mmol), KI (0.05 mmol), TBHP (1.5 mmol), and methanol (5 mL) at
65ꢀC.
bIsolated yield.
cBased on GC.
Scheme 1. Oxidative esterification on 4-nitro benzaldehyde with alcohols.
In conclusion, we have presented a facile and mild process for the conversion of
aldehyde to ester. The merits of this method are (a) it is a metal-free system, (b) a
catalytic amount of potassium iodide was required to promote the reaction, whereas
an equivalent amount of iodine was used in earlier methods, and (c) it is a green pro-
cess, where the by-products are water and t-BuOH. Moreover, this method does not
require the use of any external base. Further exploration of this method for different
organic transformations are in progress, and results will be reported in due course.
EXPERIMENTAL
1H NMR spectra were recorded on a Gemini 200-MHz or an Avance 300-MHz
spectrometer in CDCl3 with tetramethylsilane (TMS) as an internal standard. Gas
chromatographic (GC) data were recorded on a Schimdzu using BP-01 (30 M Â
0.25 mm  1.0 mm) column. GC-MS spectra were recorded on Trace DSQ GC-MS
spectrometer using BP-01 (30 M  0.25 mm  1.0 mm) column. Silica gel G (E.
Merck, India) was used for thin-layer chromatography (TLC).
General Procedure for the Synthesis of Esters from Aldehyde
A solution of 70% aqueous TBHP (1.5 mmol) was added dropwise to a solution
of aldehyde (1.0 mmol) and potassium iodide (0.05 mmol) in 5 mL of methanol over

CATALYTIC OXIDATIVE ESTERIFICATION
191
Table 3. Oxidative esterification of benzyl alcohol with methanol using KI–TBHPa
Entry
17
Substrate
Conv. (%)b
Sel. (%)b ester–aldehyde
71
98:2
18
19
60
66
98:2
52:48
20
62
94:6
21
22
23
24
66
50
45
61
100:0
77:23
96:4
87:13
25
26
59
68
98:02
86:14
aReaction conditions: aldehyde (1.0 mmol), KI (0.2 mmol), TBHP (3.0 mmol), and methanol (5 mL) at
65ꢀC, 24 h.
bBased on 1H NMR.
a period of 30 min and stirred at 65ꢀC. Progress of the reaction was monitored by
TLC, and after completion of the reaction, the mixture was quenched with saturated
aqueous Na2S2O3, washed with brine, extracted with ethyl acetate, and dried over
anhydrous Na2SO4. Removal of the solvent under vacuum afforded the crude pro-
duct, which was purified by column chromatography using a hexane=ethyl acetate
1
mixture and was analyzed by H NMR, GC, and GC-MS.

192
K. RAJENDER REDDY ET AL.
Scheme 2. Mechanism for the oxidative esterification of aldehyde with alcohols using KI–TBHP.
General Procedure for the Synthesis of Esters from Alcohol
A solution of 70% aqueous TBHP (3.0 mmol) was added to a solution of
alcohol (1.0 mmol) and potassium iodide (0.20 mmol) in 5 mL of methanol dropwise
over a period of 30 min and stirred at 65ꢀC. Progress of the reaction was monitored
by TLC, and after completion of the reaction, the mixture was quenched with
saturated aqueous Na2S2O3, washed with brine, extracted with ethyl acetate, and
dried over anhydrous Na2SO4. Removal of the solvent under vacuum afforded the
1
crude product, which was analyzed by H NMR, GC, and GC-MS.
Data
4-Nitro-benzoic acid methyl ester (Table 2, Entry 1). 1H NMR: d ¼ 4.00
(s, 3H), 8.23 (d, J ¼ 8.9, 2H), 8.31 (d, J ¼ 8.9, 2H). EI-MS (GC-MS): 181.0 (Mþ).
4-Fluoro-benzoic acid methyl ester (Table 2, Entry 2). 1H NMR: d ¼ 3.90
(s, 3H), 7.02–7.14 (m, 2H), 7.98–8.10 (m, 2H). EI-MS (GC-MS): 154.0 (Mþ).
4-Chloro-benzoic acid methyl ester (Table 2, Entry 3). 1H NMR: d ¼ 3.90
(s, 3H), 7.40 (d, J ¼ 8.8, 2H), 7.95 (d, J ¼ 8.8, 2H). EI-MS (GC-MS): 169.9 (Mþ).
4-Bromo-benzoic acid methyl ester (Table 2, Entry 4). 1H NMR: d ¼ 3.85
(s, 3H), 7.50 (d, J ¼ 7.8, 2H), 7.82 (d, J ¼ 8.6, 2H). EI-MS (GC-MS): 213.9 (Mþ).
4-Cyano-benzoic acid methyl ester (Table 2, Entry 5). 1H NMR: d ¼ 4.00
(s, 3H), 7.78 (d, J ¼ 8.7, 2H), 8.17 (d, J ¼ 8.7, 2H). EI-MS (GC-MS): 160.9 (Mþ).
1
Benzoic acid methyl ester (Table 2, Entry 6). H NMR: d ¼ 3.95 (s, 3H),
7.42–7.48 (m, 2H), 7.52–7.60 (m, 1H), 8.02–8.08 (m, 2H). EI-MS (GC-MS): 135.9 (Mþ).
4-Methyl-benzoic acid methyl ester (Table 2, Entry 7). 1H NMR:
d ¼ 2.43(s, 3H), 3.90 (s, 3H), 7.22 (d, J ¼ 8.5, 2H), 7.92 (d, J ¼ 8.3, 2H). EI-MS
(GC-MS): 150.0 (Mþ).
4-Isopropyl-benzoic acid methyl ester (Table 2, Entry 8). 1H NMR:
d ¼ 1.31 (d, J ¼ 6.8, 6H), 2.92–3.04 (m, 1H), 3.92 (s, 3H), 7.28 (d, J ¼ 8.3, 2H),
7.96 (d, J ¼ 9.0, 2H). EI-MS (GC-MS): 178.0 (Mþ).

CATALYTIC OXIDATIVE ESTERIFICATION
193
Naphthalene-1-carboxylic acid methyl ester (Table 2, Entry 9). 1H
NMR: d ¼ 4.00 (s, 3H), 7.42–7.62 (m, 4H), 7.82 (d, J ¼ 7.8, 1H), 7.98 (d, J ¼ 7.8,
1H), 8.18 (d, J ¼ 6.5, 1H), 8.94 (d, J ¼ 7.8, 1H). EI-MS (GC-MS): 185.9 (Mþ).
Isonicotinic acid methyl ester (Table 2, Entry 10). 1H NMR: d ¼ 4.00 (s,
3H), 7.86 (d, J ¼ 6.0, 2H), 8.80 (d, J ¼ 6.0, 2H). EI-MS (GC-MS): 136.9 (Mþ).
Thiophene-2-carboxylic acid methyl ester (Table 2, Entry 11). 1H NMR:
d ¼ 3.85 (s, 3H), 7.07 (t, J ¼ 8.8, 1H), 7.50 (d, J ¼ 6.6, 1H), 7.75 (d, J ¼ 3.7, 1H).
EI-MS (GC-MS): 141.8 (Mþ).
Furan-2-carboxylic acid methyl ester (Table 2, Entry 12). 1H NMR:
d ¼ 3.90 (s, 3H), 6.50 (s, 1H), 7.15 (s, 1H), 7.57 (s, 1H). EI-MS (GC-MS): 125.9 (Mþ).
Cyclohexanecarboxylic acid methyl ester (Table 2, Entry 13). 1H NMR:
d ¼ 1.22–1.52 (m, 4H), 1.62–1.94 (m, 6H), 2.24–2.34 (m, 1H), 3.66 (s, 3H). EI-MS
(GC-MS): 141.9 (Mþ).
Octanoic acid methyl ester (Table 2, Entry 14). 1H NMR: d ¼ 0.87 (t,
J ¼ 6.0, 3H), 1.24–1.64 (m, 10H), 2.26 (t, J ¼ 6.8, 2H), 3.64 (s, 3H). EI-MS (GC-MS):
158.0 (Mþ).
ACKNOWLEDGMENTS
M. V. and C. U. M. thank the Department of Biotechnology (DBT) and
the Council of Scientific Industrial Research (CSIR), India, respectively, for their
fellowships.
REFERENCES
1. Anastas, P. T.; Williamson, T. C. (Eds.). In Green Chemistry: Frontiers in Benign Chemical
Syntheses and Processes; Oxford University Press: Oxford, 1998.
2. (a) Sheldon, R. A.; Arends, I.; Ten Brink, G. J.; Dijksman, A. Green, catalytic oxidations
of alcohols. Acc. Chem. Res. 2002, 35, 774–781; (b) Caron, S.; Dugger, R. W.; Ruggeri, S.
G.; Ragan, J. A.; Ripin, D. H. B. Large-scale oxidations in the pharmaceutical industry.
Chem. Rev. 2006, 106, 2943–2989; (c) Larock, R. C. In Comprehensive Organic Transform-
ation; VCH: New York, 1999.
3. (a) Corey, E. J.; Gilman, N. W.; Ganem, B. E. New methods for the oxidation of
aldehydes to carboxylic acids and esters. J. Am. Chem. Soc. 1968, 90, 5616–5617; (b)
Ogawa, T.; Matsui, M. A novel oxidative transformation: Oxidative esterification. J.
Am. Chem. Soc. 1976, 98, 1629–1630; (c) Wilson, S. R.; Tofigh, S.; Misra, R. N. A novel,
nonoxidative method for the conversion of aldehydes to esters. J. Org. Chem. 1982, 47,
1360–1361; (d) Garegg, P. J.; Olsson, L.; Oscarson, S. Synthesis of methyl (ethyl 2-O-acyl-
3,4-di-O-benzyl-1-thio-b-D-glucopyranosid)uronates and evaluation of their use as
reactive b-selective glucuronic acid donors. J. Org. Chem. 1995, 60, 2200–2204.
4. March, J. In Advanced Organic Chemistry; John Wiley & Sons: New York, 1992; p. 392.
5. (a) Barluenga, J.; Gonzalez-Bobes, F.; Murguia, M. C.; Ananthoju, S. R.; Gonzalez, J. M.
Bis(pyridine)iodonium tetrafluoroborate (IPy2BF4): A versatile oxidizing reagent. Chem.
Eur. J. 2004, 10, 4206–4213; (b) Mcdonald, C.; Holcomb, H.; Kennedy, K.; Kirkpatrick,
E. The N-iodosuccinimide-mediated conversion of aldehydes to methyl esters. J. Org.
Chem. 1989, 54, 1213–1215; (c) Espenson, J. H.; Zhu, Z.; Zauche, T. H. Bromide ions

194
K. RAJENDER REDDY ET AL.
and methyltrioxorhenium as cocatalysts for hydrogen peroxide oxidations and bromina-
tions. J. Org. Chem. 1999, 64, 1191–1196; (d) Travis, B. R.; Sivakumar, M.; Hollist, G. O.;
Borhan, B. Facile oxidation of aldehydes to acids and esters with oxone. Org. Lett. 2003,
5, 1031–1035; (e) Gopinath, R.; Barkakaty, B.; Talukdar, B.; Patel, B. K.
Peroxovanadium-catalyzed oxidative esterification of aldehydes. J. Org. Chem. 2003, 68,
2944–2947; (f) Woo, W. J.; Li, C. J. Copper-catalyzed oxidative esterification of alcohols
with aldehydes activated by Lewis acids. Tetrahedron Lett. 2007, 48, 1033–1035; (g)
Lerebours, R.; Wolf, C. Chemoselective nucleophilic arylation and single-step oxidative
esterification of aldehydes using siloxanes and a palladium-phosphinous acid as a reaction
switch. J. Am. Chem. Soc. 2006, 128, 13052–13053; (h) Shaikh, T. M. A.; Emmanuvel, L.;
Sudalai, A. NaIO4=LiBr-mediated direct conversion of benzylic alcohols and aromatic
aldehydes to aromatic esters. Synth. Commun. 2007, 37, 2641–2646.
6. (a) Liu, R.; Liang, X.; Dong, C.; Hu, X. Transition-metal-free: A highly efficient catalytic
aerobic alcohol oxidation process. J. Am. Chem. Soc. 2004, 126, 4112–4113; (b) Miller, R.
A.; Hoerner, R. S. Iodine as a Chemoselective reoxidant of TEMPO: Application to the
oxidation of alcohols to aldehydes and ketones. Org. Lett. 2003, 5, 285–287; (c) Bjorsvik,
H. R.; Liguori, L.; Constantino, F.; Minisci, F. A New modified ‘‘Montanari oxidation
process’’ by means of chlorine dissolved in the reaction solvent as oxidant and TEMPO
as catalyst: Oxidation of 3-S-quinuclidinol to 3-quinuclidinone. Org. Process Res. Dev.
2002, 6, 197–200; (d) Corey, E. J.; Kim, C. U. Oxidation of primary and secondary
alcohols to carbonyl compounds using dimethylsulfoxide–chlorine complex as reagent.
Tetrahedron Lett. 1973, 14, 919–922; (e) Wicha, J.; Zarecki, A. Oxidation with chlorine
complexes: Specific oxidation of secondary hydroxyl groups in the presence of primary
hydroxyl groups in polyhydric alcohols. Tetrahedron Lett. 1974, 15, 3059–3062; (f)
Farkas, L.; Schachter, O. The oxidation of alcohols by bromine in the presence of
bromate. J. Am. Chem. Soc. 1949, 71, 2827–2828; (g) Hayman, B. P.; Weissmann, Y.
Oxidation of 2-propanol by bromine and by hypobromous acid in aqueous solution. J.
Am. Chem. Soc. 1969, 91, 668–672; (h) Tohma, H.; Maegawa, T.; Kita, Y. Facile and
efficient oxidative transformation of primary alcohols to methyl esters in water using
hypervalent iodine(III) reagents. Synlett 2003, 723–725.
7. Togo, H.; Iida, S. Synthetic use of molecular iodine for organic synthesis. Synlett 2006,
2159–2175, and references therein.
8. (a) Yadav, J. S.; Reddy, B. V. S.; Hashim, S. R. A new and effficent synthesis of
2,2-disubstituted-3,4-dihydro-2H-1-benzopyrans. J. Chem. Soc., Perkin Trans. 1 2000,
3082–3084; (b) Ishihara, M.; Togo, H. An efficient preparation of 2-imidazolines and imi-
dazoles from aldehydes with molecular iodine and (diacetoxyiodo)benzene. Synlett 2006,
227–230; (c) Pedras, M. S. C.; Jha, M. Concise syntheses of the cruciferous phytoalexins
brassilexin, sinalexin, wasalexins, and analogues: Expanding the scope of the vilsmeier
formylation. J. Org. Chem. 2005, 70, 1828–1834.
9. (a) Nierengarten, J.; Gramlich, V.; Cardullo, F.; Diederich, F. Regio- and diastereoselec-
tive bisfunctionalization of C60 and enantioselective synthesis of a C60 derivative with a
chiral addition pattern. Angew. Chem., Int. Ed. Engl. 1996, 35, 2101–2103; (b) Yadav, J.
S.; Reddy, B. V. S.; Rao, K. V.; Raj, K. S.; Rao, P. P.; Prasad, A. R.; Gunasekar, D. First
example of molecular iodone-catalyzed allylation and alkynylation of cyclic allylic acet-
ates. Tetrahedron Lett. 2004, 45, 6505–6507; (c) Yeh, H. C.; Yeh, S.; Chen, C. Readily
synthesised arylamino fumaronitrile for nondoped red organic light-emitting diodes.
Chem. Commun. 2003, 2632–2633; (d) Enes, R. F.; Tome, A. C.; Cavaleiro, J. A. S.;
El-Agamey, A.; McGarvey, D. J. Synthesis and solvent dependence of the photophysical
properties of [60]fullerene–sugar conjugates. Tetrahedron 2005, 61, 11873–11881.
10. (a) Dowle, M. D.; Davies, D. I. Synthesis and synthetic utility of halolactones. Chem. Soc.
Rev. 1979, 8, 171–197; (b) Cardillo, G.; Orena, M. Stereocontrolled cyclofunctionalization

CATALYTIC OXIDATIVE ESTERIFICATION
195
of double bonds through heterocyclic intermediates. Tetrahedron 1990, 46, 3321–3408; (c)
Robin, S.; Rousseau, G. Electrophilic cyclization of unsaturated amides. Tetrahedron
1998, 54, 13681–13736; (d) Ranganathan, S.; Muraleedharan, K. M.; Vaish, N. K.;
Jayaraman, N. Halo- and selenolactonasition: The two major strategies for cyclo functio-
nalisation. Tetrahedron 2004, 60, 5273–5308.
11. (a) Chavan, S. P.; Kale, R. R.; Shivasankar, K.; Chandake, S. I.; Benjamin, S. B. A simple
and efficient method for transesterification of b-ketoesters catalysed by iodine. Synthesis
2003, 2695–2698; (b) Mukhopadhyay, B.; Kartha, K. P. R.; Russell, D. A.; Field, R. A.
Streamlined synthesis of per-O-acetylated sugars, glycosyl iodides, or thioglycosides from
unprotected reducing sugars. J. Org. Chem. 2004, 69, 7758–7760; (c) Banik, B. K.; Chapa,
M.; Marguez, J.; Cardona, M. A remarkable iodine catalysed protection of carbonyl
compounds. Tetrahedron Lett. 2005, 46, 2341–2343; (d) Yadav, J. S.; Satyanarayana,
M.; Raghavendra, S.; Balanarsaiah, E. Chemoselective hydrolysis of terminal isopropyli-
dine acetals in acetonitrile using molecular iodine as a mild and efficient catalyst.
Tetrahedron Lett. 2005, 46, 8745–8748.
12. Mori, N.; Togo, H. Facile oxidative conversion of alcohols to esters using molecular
iodine. Tetrahedron 2005, 61, 5915–5925.
13. Reddy, K. R.; Maheswari, C. U.; Venkateshwar, M.; Kantam, M. L. Oxidative amidation
of aldehydes and alcohols with primary amines catalyzed by KI–TBHP. Eur. J. Org. Chem
2008, 21, 3619–3622.
14. Yamada, S.; Morizono, D.; Yamamoto, K. Mild oxidation of aldehydes to corresponding
carboxylic acids and esters: Alkaline iodine oxidation revisited. Tetrahedron Lett. 1992,
33, 4329–4332.