A facile and efficient conversion of aldehydes into 1,1-diacetates (acylals) using iron(III) fluoride as a novel catalyst

Article abstract of DOI:10.1071/CH06166

Aldehydes are smoothly converted into the corresponding 1,1-diacetates (acylals) in high yields in the presence of a catalytic amount (0.1 mol-%) of iron(III) fluoride at room temperature. The noteworthy features of the present system are shorter reaction times, chemoselective protection of aldehydes, and solvent-free conditions. The procedure is especially useful for large-scale syntheses as the catalyst is highly effective from the view of activity, selectivity, reusability, and economy in the preparation of 1,1-diacetates (acylals). CSIRO 2007.

Full text of DOI:10.1071/CH06166

Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2007, 60, 590–594
www.publish.csiro.au/journals/ajc
A Facile and Efficient Conversion of Aldehydes into
1,1-Diacetates (Acylals) using Iron(III) Fluoride
as a Novel Catalyst
V. T. Kamble,A,D R. A. Tayade,B B. S. Davane,C and K. R. KadamA
AOrganic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramananad
Teerth Marathwada University, Nanded 431 606, M.S., India.
BDepartment of Chemistry, Institute of Science, Nagpur, M.S., India.
CDepartment of Chemistry, Yeshwant College, Nanded, M.S., India.
DCorresponding author. Email: vtkd@rediffmail.com
Aldehydes are smoothly converted into the corresponding 1,1-diacetates (acylals) in high yields in the presence of a
catalytic amount (0.1 mol-%) of iron(iii) fluoride at room temperature. The noteworthy features of the present system are
shorter reaction times, chemoselective protection of aldehydes, and solvent-free conditions. The procedure is especially
useful for large-scale syntheses as the catalyst is highly effective from the view of activity, selectivity, reusability, and
economy in the preparation of 1,1-diacetates (acylals).
Manuscript received: 16 May 2006.
Final version: 18 May 2007.
OAc
Introduction
Ac2O, FeF3 (0.1 mol-%)
neat, r.t.
R
RCHO
Since protective groups play an important role in the multi-
step synthesis of complex natural products, there are always
demands for selective reagents. Among the various functional
groups, protection of the carbonyl group as a 1,1-diacetate
(acylal) is important for the following reasons. First, they are
stable under neutral and mild conditions[1] and are easily con-
verted into the parent aldehydes.[2] Second, they are used as
building blocks for the synthesis of dienes[3] and cross-linking
reagents for cellulose in cotton.[4] Hence, methods for their syn-
thesis have received considerable attention. In the literature,
there are many methods reported for the preparation of 1,1-
diaceates (acylals) from aldehydes and acetic anhydride that
employ protic acids, such as sulfuric,[5a] methanesulfonic,[5b]
phosphoric,[5c] or perchloric acid[5d] and Lewis acids, such as
PCl3,[6a] ZnCl2,[6b] TMSCI-Nal,[6c] I2,[6d] FeCl3,[6e] NBS,[6f]
anhydrous ferrous sulfate,[6g] LiBr,[6h] InCl3,[6i] WCl6,[6j]
CAN,[6k] LiBF4,[6l] and CoCl2.[6m] Some heterogeneous cat-
alysts like clay,[7a,b] zeolites,[2a,7c,d] Nafion-H,[7e] expansive
graphite,[7f] and supported reagents[7g–i] are also used. But
these procedures are often accompanied by low product
yields, longer reaction times, stringent conditions, corrosive
reagents, high catalyst loading, high temperature, and require
the use of toxic solvents. Recently, other methods that employ
catalysts like ZrCl4,[8] Zn(BF4)2,[9] Fe2(SO4)3·xH2O,[10]
Bi(NO3)3·5H2O,[11] Cu(BF4)2·xH2O,[12] KHSO4,[13] InBr3,[14]
2,4,4,6-tetrabromo-2,5-cyclohexadienone,[15] AlPW12O40,[16]
Mg(ClO4)2,[17] Zn(ClO4)2,[18] [Zr(CH3PO3)1.2(O3PC6H4SO3
H)0.8],[19] H2NSO3H,[20] silica sulfuric acid,[21] and triflates,
such as Sc(OTf)3,[2b] Cu(OTf)2,[22] LiOTf,[23] and Er(OTf)3,[24]
have been reported for the synthesis of acylals. However, the
former catalysts[8–13,15–21] are required in large amounts where
OAc
1
2
Scheme 1.
as the later triflates[2b,22–24] are costly, moisture sensitive, and
special efforts are required for their preparation. In some of
the reported methods,[23] a large excess of acetic anhydride (5–
8 equiv.) is essential for the 1,1-diacetate (acylal) formation.
Moreover, only a few reports are available for the acylation of
aldehydes using low catalyst loading (0.1 mol-%).[14,24] There-
fore, an environmentally benign reagent that can catalyze this
transformation with low catalyst loading, is still desirable.
Results and Discussion
Although iron(iii) chloride has been used widely as a Lewis
acid catalyst in a variety of organic transformations,[6e,25] the
susceptibility to aqueous media impedes its use for large-scale
synthesis. On the other hand, iron(iii) fluoride has emerged as a
mild, non-toxic, inexpensive, and water-tolerant Lewis acid cat-
alyst for various organic transformations.[26a–c] However, there
havebeennoreportsontheuseofiron(iii)fluorideforthesynthe-
sis of 1,1-diacetates (acylals) from aldehydes under solvent-free
conditions. In a continuation of our work to apply iron(iii) fluo-
ride to organic reactions in the context of green and economical
chemistry, herein, we report a facile synthesis of 1,1-diacetates
(acylals) using a small amount of iron(iii) fluoride (0.1 mol-%)
without any solvent (Scheme 1).
To optimize the reaction conditions, initially, we tried to con-
vert benzaldehyde (1 mmol) into its corresponding acylal with
iron(iii) fluoride (0.1 mol-%) and acetic anhydride (3 mmol) in
© CSIRO 2007
10.1071/CH06166
0004-9425/07/080590

Conversion of Aldehydes into Acylals with FeF3
591
Table 1. The results of the reaction of benzaldehyde (1 mmol) with
acetic anhydride (3 mmol) under different reaction conditions
Table 2. Iron(iii) fluoride catalyzed synthesis of acylals
Entry Substrate
Time [min] YieldA,B [%] Ref.
Entry
CatalystA
SolventB
Time [min]
YieldC [%]
1
C6H5CHO
5
10
10
10
15
10
10
10
15
20
20
35
35
40
10
10
10
10
10
10
8
97
96
98
98
95
96
98
97
96
95
94
94
95
93
96
95
98
97
97
96
95
98
96
96
97
92
93
[20]
[20]
[14]
[14]
[14]
[21]
[20]
[20]
[6d]
[6e]
[5b]
[12]
[6m]
[6m]
[21]
[1b]
[21]
[6a]
[5b]
[2i]
–
1
2
3
4
5
6
None
FeF3
FeF3
FeF3
FeF3
FeF3
None
MeCN
THF
CH2Cl2
Et2O
6D
90
90
90
90
5
0
72
70
65
60
97
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
4-ClC6H4CHO
4-FC6H4CHO
4-MeC6H4CHO
4-MeOC6H4CHO
4-CNC6H4CHO
4-NO2C6H4CHO
3-NO2C6H4CHO
n-C3H7CHO
n-C5H11CHO
n-C7H15CHO
None
AThe reaction was carried out in the presence of FeF3 (0.1 mol-%).
BThe reaction was carried out in 5 mL of solvent at room temperature.
CYield of pure isolated product.
DTime in hours.
1-C10H7CHO
2-C10H7CHO
1-C14H9CHO
2-Furaldehyde
the presence of various solvents and also under solvent-free con-
ditions. As shown in Table 1, in comparison to conventional
methods (Table 1, entries 2–5), the yield of the reaction under
solvent-free conditions in the presence of FeF3 (0.1 mol-%)
is higher and the reaction time is shorter (Table 1, entry 6).
However, under solvent-free conditions without catalyst, ben-
zaldehyde did not give any product even after 6 h (Table 1,
entry 1).
Thiophene-2-carboxaldehyde
(E)-PhCH=CHCHO
(E)-MeCH=CHCHO
CH2CH=CHCHO
4-(OTBDMS)C6H4CHO
3-(O-Allyl)C6H4CHO
3-(OPNB)C6H4CHO
3-(OBz)C6H4CHO
3,4-(OCH2O)C6H3CHO
3-(OPh)C6H4CHO
4-(NHBoc)C6H4CHO
4-(OTIPS)C6H4CHO
4-NMe2C6H4CHO
10
15
10
20
15
15
[9]
[2i]
[14]
[6a]
[8]
[8]
–
The reaction of benzaldehyde (10 mmol) with acetic anhy-
dride (30 mmol) in the presence of iron(iii) fluoride (0.1 mol-%)
at room temperature afforded the corresponding 1,1-diacetate
(acylal) in excellent yield (97%). The catalyst was recovered
and reused five consecutive times to give excellent yields. The
reusability of iron(iii) fluoride was examined by using benzalde-
hyde as a model substrate and the results are described in the
typical experimental procedure. The results as summarized in
Table 2 clearly reveal the scope and generality of the reaction
with respect to a variety of aliphatic and aromatic aldehydes.
The aliphatic (Table 2, entries 9–11), aromatic (Table 2, entries
1–8), and α,β-unsaturated (Table 2, entries 17–18) aldehydes
can be efficiently transformed into their corresponding 1,1-
diacetates (acylals). The tolerance of various functional groups
under the present conditions have been examined by reacting
substrates that bear Cl, F, Me, OMe, CN, and NO2 groups,
and it was found that reaction conditions are compatible with
these functional groups. Acid sensitive substrates like furfural,
thiophene-2-aldehyde (Table 2, entries 15–16) are also protected
as 1,1-diacetates (acylals) in excellent yields without any side
reactions, which are normally encountered under acidic condi-
tions. It is noteworthy that substrates that have acid sensitive
protecting groups such as O-TBDMS, O-allyl, OPNB, OBz,
–OCH2O–, OPh, OBn, NHBoc, and OTIPS (Table 2, entries 20–
27) were converted into their acylals without cleavage, which is
normally observed in strong acidic medium. The present reac-
tion conditions work equally well for naphthaldehydes (Table 2,
entries 12–13) and anthraldehyde (Table 2, entry 14) to afford
excellent yields of the corresponding 1,1-diacetates (acylals)
although the time required for conversion is slightly longer.
In almost all cases, the reactions are quicker than those of
the recently reported methods and the yields are quite high.
4-(Dimethylamino)benzaldehyde (Table 2, entry 28), however,
because of deactivation of the carbonyl group, remained unaf-
fected even when the reaction mixture was stirred at room
temperature for 20 h, and the starting material was quantitatively
recovered.
C
D
–
–
AYield of pure isolated product.
BProducts were characterized by spectroscopic analysis.
CTime in minutes.
DThe starting material remained intact.
Table 3. Conversion of benzaldehyde into geminal dicarboxylates with
acid anhydrides
Aldehyde
Anhydride (RCO)2O
Time [min]
YieldA [%]
PHCHO
PHCHO
PHCHO
R = C3H7
90
120
120
85
80
80
R = i-C3H7
R = i-C4H9
AYield of pure isolated product.
CH(OAc)2
O
CHO
O
Ac2O, FeF3 (0.1 mol-%)
ϩ
ϩ
r.t., 5 min
97%
100%
Scheme 2.
Acylation of benzaldehyde with propionic, butyric, and iso-
butyric anhydrides resulted in 80–85% yields of the gem-
dicarboxylates (Table 3).
Next, we investigated the competitive reaction for the acyla-
tion of benzaldehyde in the presence of cyclohexanone. When
a 1 : 1 mixture of benzaldehyde and cyclohexanone was allowed
to react with acetic anhydride in the presence of 0.1 mol-% FeF3
for 5 min, TLC analysis of the reaction mixture indicated com-
plete disappearance of the benzaldehyde, while cyclohexanone
remained intact, even when the mixture continued to stir for
5 h (Scheme 2). Also, in the case of acetyl benzaldehyde, the
The utility of the present method was then extended by
employing it in the formation of other gem-dicarboxylates.

592
V. T. Kamble et al.
CH(OAc)2
CHO
NaHCO3 and brine, the organic layer was dried over Na2SO4.
Evaporation of the solvent under reduced pressure gave almost
pure product. Further purification was achieved by column chro-
matography or recrystallization from ethyl acetate/hexane to
afford pure acetoxyphenylmethyl acetate (97%), identical (mp,
Ac2O, FeF3 (0.1 mol-%)
r.t., 15 min
COCH3
COCH3
94%
1
IR, and H NMR) to an authentic sample. The recovered cata-
lyst was activated by heating at 100◦C under vacuum for 2 h and
reused for the acylation of a fresh lot of benzaldehyde (10 mmol)
to afford 89% yield of acetoxyphenylmethyl acetate after 10 min.
After activation, the recovered catalyst was reused for four more
consecutive acylation reactions of benzaldehyde (10 mmol) to
afford 88, 85, 83, and 80% yields in 15, 20, 25, and 30 min,
respectively.
Scheme 3.
Table 4. Comparison of the effect of catalysts in the acylation of
4-nitrobenzaldehyde (1 equiv.) as an example
Catalyst
Catalyst load [mol-%]
Time [min]
YieldA [%]
ZrCl4
5
0.6
2
1
0.1
2
2.5
20
0.1
0.1
30
3B
1.5B
3
0.1
10
4B
15B
45
92[8]
93[9]
85[10]
92[12]
99[14]
99[2b]
94[22]
99[23]
89[16]
99
Zn(BF4)2
Fe2(SO4)3·xH2O
Cu(BF4)2·xH2O
InBr3
Sc(OTf)3
Cu(OTf)2
LiOTf
Spectroscopic Data for Some Compounds
Entry 1.
Mp 43–44◦C (lit.[20] 44–45◦C). νmax (KBr)/cm−1 700, 760,
1010, 1065, 1215, 1245, 1375, 1470, 1605, 1750, 3060. δH 2.02
(s, 6H), 7.37–7.40 (m, 3H), 7.50–7.53 (m, 2H), 7.70 (s, 1H).
AlPW12O40
FeF3
Entry 2.
10
Mp 81–82◦C (lit.[20] 82–83◦C). νmax (KBr)/cm−1 620, 780,
1010, 1210, 1375, 1480, 1605, 1760, 3020, 3060. δH 2.12 (s,
6H), 7.38–7.42 (m, 2H), 7.43–7.46 (m, 2H), 7.65 (s, 1H).
AYield of pure isolated product.
BTime in hours.
Entry 3.
aldehyde group was converted into the corresponding diacetate,
while the ketone functionality remained unaffected (Scheme 3).
This result suggests that the present protocol is useful for
carrying out similar chemoselective reactions.
Mp 51–52◦C (lit.[14] 50–51◦C). νmax (KBr)/cm−1 630, 775,
1015, 1215, 1475, 1605, 1755, 3020, 3055. δH 2.13 (s, 6H),
7.40–7.42 (m, 2H), 7.45–7.47 (m, 2H), 7.67 (s, 1H).
Furthermore, we studied the catalytic ability of other iron
salts such as FeCl3, FeBr3, and FeI3 for the synthesis of 1,1-
diacetates (acylals). Among these catalysts, FeF3 is found to
be more effective than the aforementioned catalysts. By using
0.1 mol-% of FeCl3, FeBr3, and FeI3, benzaldehyde was con-
vertedintothecorresponding1,1-diacetate(acylal)in50, 45, and
40% yield, respectively, when the reaction mixture was stirred
for 30 min. This result clearly shows the strong catalytic ability
of FeF3 in comparison with FeCl3, FeBr3, and FeI3. The catalyst
FeF3 shows better activity in comparison with FeCl3, FeBr3, and
FeI3, because of high activation of the carbonyl group.
Entry 4.
Mp 81–82◦C (lit.[14] 82–83◦C). νmax (KBr)/cm−1 625, 780,
1015, 1210, 1250, 1490, 1650, 1755, 3020, 3055. δH 2.14 (s,
6H), 2.40 (s, 3H), 7.22 (d, J 8.0, 2H), 7.42 (d, J 8.0, 2H), 7.68
(s, 1H).
Entry 5.
Mp 63–64◦C (lit.[14] 64–65◦C). νmax (KBr)/cm−1 925, 990,
1220, 1245, 1670, 1765, 3010, 3050. δH 2.10 (s, 6H), 3.75 (s,
3H), 7.45–7.47 (m, 2H), 7.48–7.51 (m, 2H), 7.68 (s, 1H).
While comparing the effect of catalysts on the acylation of
4-nitrobenzaldehyde, we found that FeF3 is more efficient than
some of the recently reported catalysts in terms of the amount
of catalyst used, yields, and reaction times (Table 4).
In conclusion, iron(iii) fluoride is a highly efficient and prac-
tical catalyst for the conversion of aldehydes into 1,1-diacetates
(acylals). The advantages include the low cost, ease of cata-
lyst handling, mild reaction conditions, short reaction times, and
excellent chemoselectivity. Moreover, the solvent-free condition
employed in the present method should make it ‘environmentally
friendly’ and useful for industrial applications.
Entry 6.
Mp 101–102◦C (lit.[21] 100–102◦C). νmax (KBr)/cm−1 815,
1010, 1220, 1250, 1385, 1490, 1765, 2225, 3070. δH 2.13 (s,
6H), 7.50–7.55 (m, 2H), 7.60–7.65 (m, 2H), 7.67 (s, 1H).
Entry 7.
Mp 124–126◦C (lit.[20] 125–127◦C). νmax (KBr)/cm−1 850, 955,
995, 1090, 1200, 1210, 1345, 1535, 1615, 1765, 2225, 3095. δH
2.10 (s, 6H), 7.55 (d, J 9, 2H), 8.0 (d, J 9, 2H), 7.50 (s, 1H).
Entry 8.
Mp 64–65◦C (lit.[20] 65–66◦C). νmax (KBr)/cm−1 735, 820, 955,
1040, 1090, 1200, 1230, 1535, 1755, 3095. δH 2.12 (s, 6H),
7.52–7.78 (m, 3H), 8.1 (d, J 7.2, 1H), 8.22 (s, 1H).
Experimental
Typical Experimental Procedure
A mixture of benzaldehyde (10 mmol) and freshly distilledAc2O
(30 mmol) was stirred at room temperature in the presence of a
catalytic amount of iron(iii) flouride (0.01 mmol) for an appro-
priate time (Table 1). After completion of the reaction, as indi-
cated byTLC, the reaction mixture was quenched with water and
extracted with ethyl acetate. After being washed with aqueous
Entry 10.
Liquid (128–129/2).[6e] νmax (neat)/cm−1 650, 990, 1015, 1090,
1205, 1235, 1375, 1460, 1750, 2960. δH 1.02 (t, J 5.6, 3H),
1.25–1.80 (m, 8H), 2.05 (s, 6H), 6.68 (s, 1H).

Conversion of Aldehydes into Acylals with FeF3
593
Entry 12.
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Mp 90–91◦C (lit.[12] 90–92◦C). νmax (KBr)/cm−1 950, 995,
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7.60 (m, 3H), 7.75 (d, J 7.0, 1H), 7.85–7.90 (m, 2H), 8.25–8.30
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Mp 84–85◦C (lit.[21] 84–86◦C). νmax (KBr)/cm−1 695, 750, 945,
1010, 1110, 1210, 1245, 1375, 1490, 1610, 1655, 1765, 2930,
3090. δH 2.12 (s, 6H), 5.92 (dd, J 16.0, 1H), 6.85 (d, J 16, 1H),
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1175. doi:10.1081/SCC-120003607
Entry 20.
Mp 91–92◦C (lit.[2i] 91–94◦C). νmax (KBr)/cm−1 690, 955,
1010, 1165, 1210, 1239, 1371, 1515, 1610, 1655, 1767, 2935.
δH 0.28 (s, 2H), 0.95 (s, 9H), 2.07 (s, 6H), 6.65 (d, J 8.2, 2H),
7.03 (d, J 8.2, 2H), 7.60 (s, 1H).
Entry 21.
Mp 39–40◦C (lit.[6a] 40–41◦C). νmax (KBr)/cm−1 925, 1010,
1165, 1210, 1250, 1370, 1430, 1525, 1625, 1767, 2990, 3035.
δH 2.10 (s, 6H), 4.55 (d, J 5.2, 2H), 5.30 (d, J 10.2, 1H), 5.45
(d, J 16.2, 1H), 5.95–6.10 (m, 1H), 6.95 (d, J 8.2, 2H), 7.45 (d,
J 8.2, 2H), 7.60 (s, 1H).
(j) B. Karimi, G. R. Ebrahiminan, H. Seradj, Synth. Commun. 2002,
32, 669. doi:10.1081/SCC-120002503
(k) S. C. Roy, B. Banerjee, Synlett 2002, 1677. doi:10.1055/S-2002-
34243
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2002, 0604. doi:10.1055/S-2002-22705
(m) A. J. Fry, A. K. Rho, L. R. Sherman, C. S. Sherwin, J. Org. Chem.
1991, 56, 3283. doi:10.1021/JO00010A021
Entry 23.
Mp 52–54◦C (lit.[2i] 52–55◦C). νmax (KBr)/cm−1 825, 1010,
1167, 1225, 1375, 1511, 1605, 1750, 2930. δH 2.12 (s, 6H), 5.15
(s, 2H), 7.11 (d, J 8.2, 2H), 7.42 (m, 5H), 7.63 (s, 1H), 7.80 (d,
J 8.2, 2H).
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Mp 79–80◦C (lit.[14] 78–79◦C). νmax (KBr)/cm−1 790, 825, 930,
1005, 1040, 1150, 1225, 1365, 1445, 1490, 1605, 1755, 2955.
δH 2.03 (s, 6H), 5.85 (s, 2H), 6.65 (m, 3H), 7.50 (s, 1H).

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