Indium trichloride catalyzed chemoselective conversion of aldehydes to gem-diacetates

Article abstract of DOI:10.1081/SCC-120005425

Aldehydes are chemoselectively converted into the corresponding gem-diacetates at ambient temperature in high to quantitative yields using a catalytic amount of indium(III) chloride. The deprotection of the resulting gem-diacetates is achieved using the s

Full text of DOI:10.1081/SCC-120005425

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INDIUM TRICHLORIDE CATALYZED CHEMOSELECTIVE
CONVERSION OF ALDEHYDES TO GEM-DIACETATES*
a
a
a
J. S. Yadav , B. V. Subba Reddy & Ch. Srinivas
a
Division of Organic Chemistry , Indian Institute of Chemical Technology , Hyderabad, 500
07, India
0
Published online: 18 Oct 2011.
To cite this article: J. S. Yadav , B. V. Subba Reddy & Ch. Srinivas (2002) INDIUM TRICHLORIDE CATALYZED CHEMOSELECTIVE
CONVERSION OF ALDEHYDES TO GEM-DIACETATES*, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:14, 2149-2153, DOI: 10.1081/SCC-120005425
To link to this article: http://dx.doi.org/10.1081/SCC-120005425
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 14, pp. 2169–2174, 2002
INDIUM TRICHLORIDE CATALYZED
CHEMOSELECTIVE CONVERSION OF
ALDEHYDES TO GEM-DIACETATES*
y
J. S. Yadav, B. V. Subba Reddy, and Ch. Srinivas
Division of Organic Chemistry, Indian Institute of
Chemical Technology, Hyderabad 500 007, India
ABSTRACT
Aldehydes are chemoselectively converted into the corre-
sponding gem-diacetates at ambient temperature in high to
quantitative yields using a catalytic amount of indium(III)
chloride. The deprotection of the resulting gem-diacetates is
achieved using the same catalyst in the presence of water.
Aldehydes react with acetic anhydride in the presence of acid catalysts
[
to form gem-diacetates, which are important precursors for the synthesis
1]
of acetoxy dienes and dihalo vinyl acetates. Acylals are useful as cross
[2]
[3]
linking reagents for cellulose in cotton and serve as activators in the
composition of bleaching mixture used for the treatment of wine-stained
fabrics. In addition, gem-diacetates are also used as substrates in nucelo-
[
4]
philic substitution reactions. Due to the remarkable stability of gem-
diacetates towards a variety of reaction conditions, they are also gaining
importance in organic synthesis as an alternative to acetals for the
*
IICT Communication No. 4628.
Corresponding author. E-mail: yadav@iict.ap.nic.in
y
2
169
DOI: 10.1081/SCC-120005425
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

2
170
YADAV, REDDY, AND SRINIVAS
protection of aldehydes. Generally, they are prepared from aldehydes and
[
5]
[6]
acetic anhydride using strong Bronsted acids or Lewis acids but these
procedures are often accompanied by longer reaction times or low yields of
products in case of aliphatic aldehydes. Recently, metal triflates and
[
7]
N-bromo succinimide are also found to effect this transformation.
However, many of these methods involve strongly acidic or oxidizing
conditions, expansive and hazardous reagents, longer reaction times and
cumbersome experimental/isolation procedures. Further very few methods
are known for the chemoselective acetalization of aldehydes in presence of
ketones. Therefore, there is need to develop a mild, convenient and high
yielding protocol for the conversion of aldehydes to gem-diacetates.
[
8]
Recently, indium halides have emerged as potential Lewis acids imparting
high regio-and chemoselectivity in various chemical transformations due to
their exceptional stability, reactivity and recoverability from water. In view
of the recent surge in activity on the use of InCl as a mild Lewis acid, we
3
report herein a novel and highly efficient protocol for the chemoselective
conversion of aldehydes into gem-diacetates using indium trichloride
(
Scheme 1).
Scheme 1.
In a similar fashion, several aldehydes reacted well with acetic anhy-
dride to give the corresponding acylals in high yields. In all the cases the
reactions proceeded smoothly at ambient temperature and the products
were obtained in excellent yields with high chemoselectivity. The procedure
offers good selectivity for the protection of aldehydes in the presence of
ketones. The ketones like cyclohexanone, acetophenone, 3-pentanone did
not yield any acylals under the present reaction conditions and in the case of
substrates bearing both aldehyde and ketone functionalities, the keto group
remains unaffected with aldehyde getting converted into diacetate (Entry-k).
This indicated that the chemoselective protection of an aldehyde in the
presence of ketone could be achieved by this procedure. These reactions,
however, did not proceed in the absence of InCl . Both aromatic and ali-
3
phatic aldehydes gave the corresponding acylals in high yields (80–96%) in a
short reaction time (0.5–2.0 h). However, aromatic aldehydes with electron
withdrawing groups and bulky substrates like anthracene-9-carboxaldehyde
required comparatively longer reaction time (2–4 h) to achieve complete

ALDEHYDE CONVERSION TO GEM-DIACETATES
2171
conversion. The products were obtained in pure form after aqueous work-
up without further purification. The water soluble substrate like phenyl
glyoxal hydrate, was also chemoselectively converted into their correspond-
ing gem-diacetate in high yield using 10% indium trichloride and 2 moles of
acetic anhydride per mole of aldehyde. The acid sensitive substrates like
furfural and cinnamaldehyde were also converted into gem-diacetates in
high yields without the formation of any side products, which are normally
observed under strongly acidic conditions. Further, the reaction of acylals
derived from aldehydes with water in the presence of 10% indium(III)
chloride gave the parent aldehydes in high yields in a short reaction time
(
Scheme 2).
Scheme 2.
Similarly, several acylals were deprotected to the corresponding alde-
hydes using the same catalyst by a mere variation in the experimental pro-
tocol. The tolerance of various functional groups under the present reaction
conditions have been examined by reacting the substrates bearing OBn,
OPh, OMe, methylenedioxy, cyano and olefinic groups. Finally, chemo-
selectivity of the present method was observed by the use of keto aldehydes.
Several examples illustrating this novel and rapid procedure for the prepara-
tion of gem-diacetates are summarized in Table 1.
In summary, InCl is found to be a superior Lewis acid for the
3
chemoselective conversion of aldehydes into gem-diacetals under mild reac-
tion conditions. The possibility of deprotection using the same catalyst with
slight change in experimental protocol makes it an attractive strategy, offer-
ing advantages over methods, which use difference catalysts for protection
and deprotection of aldehydes.
EXPERIMENTAL
1
Melting points were recorded on Buchi R535 apparatus. H NMR
spectra were recorded on Varian Gemini-200 spectrometer. Mass spectra

2
172
YADAV, REDDY, AND SRINIVAS

ALDEHYDE CONVERSION TO GEM-DIACETATES
2173
were recorded on micromass 7070H mass spectrometer operating at 70 eV.
Thin layer chromatography was performed on precoated silica gel 60f 245
(
0.5 mm) glass plates.
General Procedure
Acetylation of aldehydes: A mixture of aldehyde (5 mmol), freshly
distilled acetic anhydride (5 mmol) and InCl3 (10 mol%) in dichloro-
methane (15 mL) was stirred at ambient temperature for an appropriate
time, After complete conversion, as indicated by TLC, the reaction
mixture was poured into saturated sodium bicarbonate solution (30 mL)
and extracted twice with dicholoromethane (2 Â 15 mL). The combined
organic layers were dried, concentrated in vacuo to afford the pure
diacetate.
Deacetylation of aldehydes: A solution of diacetate (5 mmol) and InCl3
10 mol%) in water (5 mL) was stirred at room temperature for an appro-
(
priate time as required to complete the reaction. After complete conversion,
as indicated by TLC, the reaction mixture was diluted with water and
extracted twice with dichloromethane (2 Â 10 mL). The combined organic
layers were dried over anhydrous Na SO and concentrated in vacuo to give
2
4
the corresponding aldehyde. Spectral data for product 2f: solid, m.p. 84–85
1
[
5]
(
lit. 84–86) H NMR (CDCl ): ꢀ ¼ 2.15 (s, 6H), 5.95 (dd, 1H, J ¼ 16.5 and
3
þ
7
1
9
.2 Hz), 6.85 (d, 1H, J ¼ 16.5), 7.20–7.45 (m, 6H). EIMS: m/z: 234 M , 191,
75, 132, 101, 91. IR (KBr): 3035, 2955, 1750, 1680, 1490, 1240, 1015,
70 cm
ꢁ
1
.
1
2
k: H NMR (CDCl ): ꢀ ¼ 2.20 (s, 6H), 7.80 (t, 2H, J ¼ 8.2 Hz), 7.60 (s,
3
þ
1
7
H), 7.65 (m, 1H), 7.95 (d, 2H, J ¼ 8.2 Hz). EIMS: m/z: 236 M , 193, 105,
ꢁ
1
7, 51, 43. IR (KBr): 3025, 2970, 1760, 1720, 1210, 1080 cm
.
[
5]
1
2
m: Solid, m.p. 65–67 (lit. 66–67) H NMR (CDCl ): ꢀ ¼ 2.15 (s, 6H),
3
7
.10 (dd, 1H, J ¼ 5.0, 4.5 Hz), 7.30 (d, 1H, J ¼ 4.5 Hz), 7.40 (d, 1H,
þ
J ¼ 5.0 Hz), 7.90 (s, 1H). EIMS: m/z: 214 M , 171, 155, 112, 85. IR
ꢁ
1
neat): 3025, 2955, 1750, 1765, 1465, 1240, 1015, 845 cm .
(
[
5]
1
2
p: Solid, m.p. 201–203 (lit. 204) H NMR (CDCl ): ꢀ ¼ 2.20 (s, 6H),
3
7
.40–7.55 (m, 4H), 8.05 (d, 2H, J ¼ 8.5 Hz), 8.45 (s, 1H), 8.75 (d, 2H,
þ
J ¼ 8.5 Hz), 9.25 (s, 1H). EIMS: m/z: 308 M , 265, 249, 206, 190, 177. IR
ꢁ
1
neat): 3020, 2950, 1740, 1650, 1520, 1240, 1020, 935 cm .
(
[
5]
1
2
q: Liquid, 127–129/2 mm (lit. 128/2 mm) HNMR (CDCl ): ꢀ ¼ 0.95
3
(
t, 3H, J ¼ 6.5 Hz), 1.25–1.5 (m ,6H), 1.80 (m, 2H), 2.15 (s, 3H), 6.70 (t, 1H,
þ
J ¼ 6.0 Hz). EIMS: m/z: 202 , 159, 143, 100, 84. IR (neat): 3010, 2930, 2870,
ꢁ1
1
750, 1465, 1245, 1030, 945 cm .

2
174
YADAV, REDDY, AND SRINIVAS
ACKNOWLEDGMENTS
BVS and ChS thank CSIR, New Delhi, for the award of fellowships.
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Received in Japan May 22, 2001