Copper(II) tetrafluoroborate-catalyzed formation of aldehyde-1,1-diacetates

Article abstract of DOI:10.1055/s-2004-816000

Aldehyde 1,1-diacetates are farmed in excellent yields from aldehydes and acetic anhydride under solvent-free conditions at room temperature in short times in the presence of a catalytic amount of copper(II) tetrafluoroborate hydrate.

Full text of DOI:10.1055/s-2004-816000

SHORT PAPER
831
Copper(II) Tetrafluoroborate-Catalyzed Formation of Aldehyde-1,1-di-
acetates
C
A
opper(II) Tetraflu
s
oroborate
i
-Cataly
t
ze
d
Formatio
K
nof Aldehyde-1,1
.
-diacetate
s
Chakraborti,* Ramasamy Thilagavathi, Raj Kumar
National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar, Punjab – 160062, India
Fax +91(172)2214692; E-mail: akchakraborti@niper.ac.in
Received 21 January 2004; revised 4 February 2004
Dedicated to Prof. Harkishan Singh.
Table 1 Cu(BF ) ·xH O Catalyzed 1,1-Diacetate Formation of Dif-
4
2
2
Abstract: Aldehyde 1,1-diacetates are formed in excellent yields
from aldehydes and acetic anhydride under solvent-free conditions
at room temperature in short times in the presence of a catalytic
amount of copper(II) tetrafluoroborate hydrate.
a
ferent Aldehydes with Ac O
2
Entry
Substrate
Time
min)
Yield
(%)
b,c
(
Keywords: 1,1-diacetates, copper compounds, catalysis, solvent-
free reactions
R2
CHO
R1
1
2
1
2
R = R = H
2
2
95
The formation of 1,1-diacetates (acylals) constitutes a
valuable method for the protection of aldehydes because
acylals are generally stable under neutral, acidic, and ba-
sic media adopted for routine work-up procedures.1 In
addition to serve as a masked aldehyde function, the 1,1-
diacetates find numerous applications. The ambident na-
1
94d
R = H
2
R = Me
–3
1
3
4
5
6
7
8
9
R = H
2
2
2
2
1
3
2
2
96
92
95e
2
R = OMe
4
1
ture of 1,1-diacetates, makes them synthetically impor-
R = H
5
2
tant precursors of 1-acetoxydienes and 2,2-dichlorovinyl
R = Cl
6
acetate for Diels–Alder reactions. Compounds bearing
1
R = H
the 1,1-diacetate functionality are used as cross-linking
2
R = F
7
agents for cellulose in cotton and activators in the compo-
sition of bleaching mixtures for wine-stained fabrics.8
1
88f
R = H
2
R = OCOPh
Classically, acylal formation involves the reaction of alde-
9
hydes with Ac O in the presence of strong protic acids.
1
92e
2
R = H
1
0
2
Various organic and inorganic Lewis-acid catalysts that
include metal halides, solid acids, metal tetrafluorobo-
R = CF
3
1
1
12
1
1
3
14
R = H
92
90
94
rates, and metal triflates have been introduced. The ex-
isting methodologies of acylal formation suffer from
disadvantages such as prolonged reaction times, high tem-
peratures, use of solvents, use of moisture sensitive and
costly catalysts, special efforts being required to prepare
2
R = NO
2
1
R = NO
2
2
R = H
1
1
0
R = H
the catalyst (e.g., Nafion-H, FeCl –SiO ), need to use ex-
2
3
2
R = CN
cess Ac O, and requirement of special apparatus. Thus,
2
R1
there was a necessity to develop a better catalyst for 1,1-
diacetate formation.
R2
Recently, we reported that metal tetrafluoroborates acti-
1
vate anhydrides for the acylation of alcohols, phenols, thi- 11
R = CHO
3
93
1
5
2
ols, and amines. We disclose herein our findings on the
catalytic effects of Cu(BF ) ·xH O for 1,1-diacetate for-
R = H
4
2
2
1
90g
1
1
1
2
3
4
R = H
2
mation from aldehydes.
2
R = CHO
1
97f
94g
R = CHO
20
20
2
R = OMe
CHO
SYNTHESIS 2004, No. 6, pp 0831–0833
x
x
.
x
x
.2
0
0
4
Advanced online publication: 05.03.2004
DOI: 10.1055/s-2004-816000; Art ID: Z01404SS.pdf
Georg Thieme Verlag Stuttgart · New York
©

8
32
A. K. Chakraborti et al.
SHORT PAPER
Table 1 Cu(BF ) ·xH O Catalyzed 1,1-Diacetate Formation of Dif- and aliphatic aldehydes. However, no diacetate formation
4
2
2
a
ferent Aldehydes with Ac O (continued)
2
was observed for acetophenone (entry 21). The reaction
rate was found to be dependent on the steric crowding sur-
rounding the aldehyde group. Thus, the presence of the
OMe group in 2-methoxy-1-naphthaldehyde (entry 13)
Entry
Substrate
Time
min)
Yield
(%)
b,c
(
CHO
necessitates the use of excess of Ac O and longer reaction
2
R
time. The two peri hydrogens in 9-anthraldehyde (entry
14) offer steric inhibition for the diacetate formation re-
sulting in an increase in the reaction time.
1
1
5
6
R = Ph
10
1
96h
88
R = Me
R
In conclusion, Cu(BF ) ·xH O is a novel and highly effi-
4
2
2
cient catalyst for 1,1-diacetate formation from aldehydes.
The advantages are high yields, fast reaction, low cost of
the catalyst, and operation at room temperature. With the
increasing tight legislation on the release of waste and use
of toxic substances as a measure to control environmental
pollution,16 the solvent-free conditions employed in the
present method make it ‘environmentally friendly’.
CHO
1
1
7
8
R = H
R = Ph
1
3
92
94
X
CHO
1
2
2
9
0
1
X = O
10
83
90
–i
X = S
10
1
,1-Diacetate Formation; Typical Procedure
O
Me
50 h
Ac O (0.35 mL, 3.75 mmol, 1.5 equiv) was added to 4-nitrobenzal-
2
dehyde (0.37 g, 2.5 mmol) in the presence of Cu(BF ) ·xH O(6 mg,
4
2
2
0
.025 mmol, 1 mol%) and the mixture was stirred magnetically un-
a
The aldehyde was treated with Ac O (1.5 equiv except for entries 6,
2
der neat conditions at r.t. till complete consumption of the aldehyde
had occurred (3 min, TLC). The reaction mixture was diluted with
EtOAc (15 mL), washed with brine (2 × 10 mL), dried (Na SO ),
1
2–14) in the presence of Cu(BF ) ·xH O (1 mol%) under neat condi-
4 2 2
tions at r.t.
2
4
b
Isolated yield of the corresponding 1,1-diacetate.
Except for entries 7, 11, and 13, all of the products were known and
and concentrated to afford the product (0.58 g, 92%), which was in
c
1
13
full agreement with the mp and spectral data (IR, H and C NMR,
and EIMS) of an authentic sample of diacetoxy(4-nitrophe-
nyl)methane. This general procedure was followed for the diacetate
formation of the remaining substrates. In all of the cases, the prod-
uct obtained after the usual work up gave satisfactory spectral (IR,
NMR, and MS) data without any further purification. Wherever ap-
plicable, purification was performed through crystallization in n-
hexane.
gave satisfactory spectral data (IR, NMR, and MS).
d
A 96% yield was obtained in carrying out the reaction with 1 equiv
of Ac O for 10 min.
2
e
A 95% yield was obtained in carrying out the reaction with 1 equiv
of Ac O for 2 min.
2
f
The reaction was carried out with 2.5 equiv of Ac O.
2
g
The reaction was carried out with 3 equiv of Ac O.
2
h
A 95% yield was obtained in carrying out the reaction with 1 equiv
of Ac O for 12 min.
The starting material remained intact.
2
i
Diacetoxy-1-(4-trifluoromethylphenyl)methane (Table 1, entry
7
)
Mp 31–33 °C.
Diverse aldehydes were subjected to 1,1-diacetate forma-
IR (neat): 1764 cm–1.
tion by the treatment with Ac O under the catalytic influ-
2
1
H NMR (300 MHz, CDCl ): d = 2.13 (s, 6 H), 7.67 (s, 4 H), 7.76
3
ence of Cu(BF ) ·xH O (Table 1). Optimum conditions
4
2
2
(s, 1 H).
for the reaction are 1.5 equivalents of Ac O in the absence
2
13
C NMR (300 MHz, CDCl ): d = 20.26, 88.56, 121.83, 125.32,
3
of solvent at room temperature. The use of 1 equivalent of
1
25.36, 127.02, 131.19, 131.62, 139.18, 168.45.
Ac O afforded comparable results, however, required rel-
2
Anal. Calcd for C H F O (276.2): C, 52.18; H, 4.01. Found: C,
1
2
11
3
4
atively longer reaction times and in some cases the reac-
tion did not proceed to completion as the solid product,
which formed trapped the starting aldehydes. The rate of
5
2.15; H, 4.03.
Diacetoxy(1-naphthyl)methane (Table 1, entry 11)
the reaction was found to be very fast and in most of the Mp 90–92 °C.
cases the diacetate formation was completed in 1–20 min-
utes (TLC, IR, NMR) with excellent yields. The progress
of the reaction can be monitored visually. For aromatic al-
dehydes, a clear solution is obtained after the addition of
IR (KBr): 1760 cm–1.
1
H NMR (300 MHz, CDCl ): d = 2.13 (s, 6 H), 7.44–7.59 (m, 3 H),
3
7
.71 (d, J = 6.9 Hz, 1 H), 7.88–7.91 (m, 2 H), 8.24–8.27 (m, 2 H).
1
3
C NMR (300 MHz, CDCl ): d = 20.82, 89.55, 124.06, 124.88,
3
Ac O, and the formation of a solid (except for entries 1, 3,
2
1
26.00, 126.69, 127.68, 128.70, 130.22, 130.55, 133.89, 168.71.
and 7) indicates completion of the reaction. For aliphatic
aldehydes, the reaction becomes exothermic after the ad-
Anal. Calcd for C H O (258.2): C, 69.76; H, 5.46. Found: C,
1
5
14
4
6
9.72; H, 5.47.
dition of Ac O, indicating the completion of diacetate for-
2
mation. In general, the products obtained after work-up
were clean (spectral analyses) and did not require any fur-
ther purification. The reaction works well for aromatic
Diacetoxy(2-methoxy-1-naphthyl)methane (Table 1, entry 13)
Mp 130–132 °C.
IR (KBr): 1752 cm–1.
Synthesis 2004, No. 6, 831–833 © Thieme Stuttgart · New York

SHORT PAPER
Copper(II) Tetrafluoroborate-Catalyzed Formation of Aldehyde-1,1-diacetates
833
1
H NMR (300 MHz, CDCl ): d = 2.09 (s, 6 H), 4.01 (s, 3 H), 7.26
(8) Eanderson, W. R. Eur. Pat. Appl. EP 125 781, 1985; Chem.
3
(
(
d, J = 8.3 Hz, 1 H), 7.36-7.41 (m, 1 H,), 7.50–7.55 (m, 1 H), 7.79
d, J = 8.0 Hz, 1 H), 7.87 (d, J = 9.1 Hz, 1 H), 8.42 (d, J = 8.6 Hz,
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(9) (a) H PO : Davey, W.; Gwilt, J. R. J. Chem. Soc. 1957,
3
4
1
H), 8.66 (s, 1 H).
1008. (b) H SO : Tomita, M.; Kikuchi, T.; Bessho, K.; Hori,
2 4
1
3
T.; Inubushi, Y. Chem. Pharm. Bull. 1963, 11, 1484.
c) HClO : Marshall, J. A.; Wuts, P. G. M. J. Org. Chem.
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3
(
4
1
1
16.08, 123.82, 125.22, 126.87, 128.47, 129.45, 131.71, 132.26,
55.78, 168.73.
1
977, 42, 1794. (d) MeSO H: Freeman, I.; Karchefski, E.
3
M. J. Chem. Eng. Data 1977, 22, 355.
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6
16
16
5
(10) (a) PCl : Michie, J. K.; Miller, J. A. Synthesis 1981, 824.
3
6.62; H 5.61.
(
b) I : Deka, N.; Kalita, D. J.; Borah, R.; Sarma, J. C. J. Org.
2
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Acknowledgment
(
11) (a) ZnCl : Scriabine, I. Bull. Soc. Chim. Fr. 1961, 1194.
2
(
b) FeCl : Trost, B. M.; Lee, C. B.; Weiss, J. M. J. Am.
RT thanks CSIR, New Delhi, India, for the award of a Senior Rese-
arch Fellowship.
3
Chem. Soc. 1995, 117, 7247. (c) See also: Wang, C.; Li, M.
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3
Subba Rao, B. V.; Srinivas, Ch. Synth. Commun. 2002, 32,
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12) (a) Nafion-H: Olah, G. A.; Mehrotra, A. K. Synthesis 1982,
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Synthesis 2004, No. 6, 831–833 © Thieme Stuttgart · New York