Lithium trifluoromethanesulfonate (LiOTf) as a recyclable catalyst for highly efficient acetylation of alcohols and diacetylation of aldehydes under mild and neutral reaction conditions

Article abstract of DOI:10.1021/jo026678+

A variety of alcohols and aldehydes were reacted with acetic anhydride at room temperature in the presence of a catalytic amount of lithium triflate (LiOTf) to produce the corresponding esters and 1,1-diacetates, respectively, in good to excellent yields under essentially neutral reaction conditions. Sensitive functional groups such as PhCO₂-, OMe, and OTBDMS ethers survived intact under the described reaction conditions.

Full text of DOI:10.1021/jo026678+

SCHEME 1
Lith iu m Tr iflu or om eth a n esu lfon a te (LiOTf)
a s a Recycla ble Ca ta lyst for High ly
Efficien t Acetyla tion of Alcoh ols a n d
Dia cetyla tion of Ald eh yd es u n d er Mild a n d
Neu tr a l Rea ction Con d ition s
types of structurally diverse alcohols with acetic anhy-
dride. Although these methods ensure good results in
many instances, there is still a great demand for mild
and especially neutral catalysts to generate esters. In our
development of new methods for functional group trans-
formation, we have been especially interested in explor-
ing the potential uses of various types of neutral cata-
lysts.9 In this regard, we have found that LiOTf is a mild
and neutral Lewis acid catalyst for highly chemoselective
dithioacetalization of aldehydes,10 transdithioacetaliza-
tion of acetals and acylals,11 and chemoselective tetrahy-
dropyranylation of alcohols under neutral reaction con-
ditions.12 LiOTf has also been shown to be a good catalyst
for the chemoselective aminolysis of oxiranes and glyco-
sylation of nucleophiles under mild and neutral reaction
conditions.13 In this paper, we wish to disclose a new mild
and efficient protocol for acetylation of a variety of
alcohols using Ac2O (5-8 equiv) in the presence of
catalytic amounts of LiOTf (0.2 equiv) under neutral
conditions (Scheme 1).
Babak Karimi* and J afar Maleki
Department of Chemistry, Institute for Advanced Studies in
Basic Sciences (IASBS), P.O. Box 45195-159,
Gava Zang, Zanjan, Iran
karimi@iasbs.ac.ir
Received November 8, 2002
Abstr a ct: A variety of alcohols and aldehydes were reacted
with acetic anhydride at room temperature in the presence
of a catalytic amount of lithium triflate (LiOTf) to produce
the corresponding esters and 1,1-diacetates, respectively, in
good to excellent yields under essentially neutral reaction
conditions. Sensitive functional groups such as PhCO2-,
OMe, and OTBDMS ethers survived intact under the
described reaction conditions.
Compounds that we acetylated in this protocol are
primary, allylic, benzylic, hindered and unhindered
secondary, and sterically hindered tertiary alcohols, the
results of which are summarized in Table 1. We first
examined the acetylation of benzyl alcohol using Ac2O
(5.0 equiv) in the absence of LiOTf. The reaction was very
sluggish so that the corresponding acetate was formed
in low yield even after 24 h (Table 1, entry 1). However,
in the case of simple primary and secondary alcohols, the
reactions progressed smoothly at room temperature in
the presence of LiOTf to afford excellent yields of the
corresponding acetate esters (Table 1, entries 2-13).
Moreover, primary and secondary allylic alcohols under-
went smooth acetylation under the same reaction condi-
tions (Table 1, entries 14-16). In general, it is known
that diaryl carbinols can also easily dimerize in the
presence of acidic catalyst.14
The acetylation of alcohols is one of the most frequently
employed reactions in organic synthesis that is normally
carried out using acetic anhydride or acetyl chloride in
the presence of tertiary amine bases such as either
pyridine or triethylamine,1 protonic or Lewis acids,2 or
sometimes solid acid catalyst.3 The rate of acetylation in
the basic conditions is known to be raised multifold if
4-(dimethylamino)pyridine (DMAP) is used as a cocata-
lyst.4 In 1993, Vedejs et al. introduced Bu3P as a less
basic catalyst than amines for acetylation of alcohols.5
Very recently, it has been shown that metal triflates such
as Sc(OTf)3 and Bi(OTf)3 as well as Me3SiOTf 8 are
excellent catalysts for efficient acetylation of various
6
7
(1) (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; Wiley: New York, 1999. (b) Kocienski, P. J .
Protecting Groups; Thieme, New York, 1994.
(2) (a) Larock, R. C. Comprehensive Organic Transformations; VCH
Publishers, Inc.: New York, 1989; p 980. For more recent leading
references, see: (b) Saravanan, P.; Singh, V. K. Tetrahedron Lett. 1999,
40, 2611. (c) Chandrasekhar, S.; Ramachander, T.; Takhi, M. Tetra-
hedron Lett. 1998, 39, 3263. (d) Damen, E. W. P.; Braamer, L.;
Scheeren, H. W. Tetrahedron Lett. 1998, 39, 6081. (e) Orita, A.;
Mitsutome, A.; Otera, J . J . Org. Chem. 1998, 63, 2420. (f) Breton, G.
W. J . Org. Chem. 1997, 62, 8952. (g) Orita, A.; Sakamoto, K.; Hamada,
Y.; Mitsutome, A.; Otera, J . Tetrahedron 1999, 55, 2899. (h) Karimi,
B.; Seradj, H. Synlett 2001, 519. (i) Iqbal, J .; Srivastava, R. R. J . Org.
Chem. 1992, 57, 2001.
(3) (a) Li, T. S.; Li, A. X. J . Chem. Soc., Perkin Trans. 1 1998, 1913.
(b) Ballini, R.; Bosica, G.; Carloni, L.; Maggi, R.; Sartori, G. Tetrahedron
Lett. 1998, 39, 6049. (c) Bhaskar, P. M.; Loganathan, D. Tetrahedron
Lett. 1998, 39, 2215.
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Engl. 1978, 17, 569. (b) Scriven, E. F. V. Chem. Soc. Rev. 1983, 12,
129.
However, benzhydrol as a model substrate was acety-
lated in 91% yield using Ac2O (6.0 equiv) in the presence
(7) Orita, A.; Tanahashi, C.; Kakuda, A.; Otera, J . Angew. Chem.,
Int. Ed. 2000, 39, 2877.
(8) (a) Procopiou, P. A.; Baugh, S. P. D.; Flack, S. S.; Inglis, G. G.
A. J . Org. Chem. 1998, 63, 2342. (b) Procopiou, P. A.; Baugh, S. P. D.;
Flack, S. S.; Inglis, G. G. A. J . Chem. Soc., Chem. Commun. 1996, 2625.
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Karimi, B.; Ebrahimian, G. R.; Seradj, H. Org. Lett. 1999, 1, 1737. (c)
Karimi, B.; Seradj, H. Synlett 2000, 641. (d) Karimi, B.; Miri Ashtiani,
A. Chem. Lett. 1999, 1199. (e) Karimi, B.; Seradj, H.; Ebrahimian, G.
R. Synlett 1999, 1456. (f) Firouzabadi, H.; Iranpoor, N.; Karimi, B.
Synthesis 1999, 58. (g) Karimi, B.; Seradj, H.; Tabaei, M. R. Synlett
2000, 1798. (h) Karimi, B.; Golshani, B. Synthesis 2002, 784. (i) Karimi,
B.; Zareyee, D. Synlett 2002, 346.
(5) (a) Vedejs, E.; Diver, S. T. J . Am. Chem. Soc. 1993, 115, 3358.
(b) Vedejs, E.; Bennett, N. S.; Conn, L. M.; Diver, S. T.; Gingras, M.;
Lin, S.; Oliver, P. A.; Peterson, M. J . J . Org. Chem. 1993, 58, 7286.
(6) (a) Ishihara, K.; Kubota, M.; Kurihara, H.; Yamamoto, H. J . Am.
Chem. Soc. 1995, 117, 6639. (b) Ishihara, K.; Kubota, M.; Kurihara,
H.; Yamamoto, H. J . Org. Chem. 1996, 61, 4560. (c) Ishihara, K.;
Kubota, M.; Yamamoto, H. Synlett 1996, 265. (d) Barrett, A. G. M.;
Braddock, D. C. Chem. Commun. 1997, 351. (e) Zhao, H.; Pendri, A.;
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40, 4055.
(11) Firouzabadi, H.; Eslami, S. Karimi, B. Bull. Chem. Soc. J pn.
2001, 74, 2401.
(12) Karimi, B.; Maleki, J . Tetrahedron Lett. 2002, 43, 5353.
(13) (a) Auge, J .; Leroy, F. Tetrahedron Lett. 1996, 37. 7715. (b)
Lubineau, A.; Drouillat, B. J . Carbohydr. Chem. 1997, 16, 1179.
(14) Gauttret, P.; El-Ghamarti, S.; Legrand, A.; Coutrier, D.; Rigo,
B. Synth. Commun. 1996, 26, 707.
10.1021/jo026678+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/09/2003
J . Org. Chem. 2003, 68, 4951-4954
4951

TABLE 1. Acetyla tion of Alcoh ols Usin g Ac2O in th e
P r esen ce of LiOTf a t Room Tem p er a tu r e
SCHEME 2
thetically important precursors for the preparation of
1-acetoxydienes, valuable synthetic intermediates for
Diels-Alder cycloaddition reactions. In general, the
preparation of 1,1-diacetates was achieved under the
catalysis of strong protonic acids such as H2SO4,17 H3-
PO4, and CH3SO3H.18 However, in recent years, Lewis
acids such as ZnCl2,19 FeCl3,16 PCl3,20 I2,21 Sc(OTf)3,22
NBS,23 and also inorganic solid catalysts like Nafion-H,24
Zeolites,25 and clay26 have received attention for this
purpose. Very recently, it has been shown that LiBF4 is
a mild and efficient Lewis acid catalyst for the conversion
of aldehydes into 1,1-dicarboxylates.27 Once again, we
observed that no considerable amount of the correspond-
ing 1,1-diacetate was formed upon the reaction of benz-
aldehyde with Ac2O in the absence of LiOTf (Table 2,
entry 1). On the other hand, with the use of acetic
anhydride (5-8 equiv), various types of aromatic alde-
hydes can effectively be converted into 1,1-diacetates in
the presence of a catalytic amount of LiOTf (0.2 equiv)
under neutral conditions (Scheme 2, Table 2). Moreover,
the protocol could also equally work with aliphatic as well
as R,â-unsaturated aldehydes (Table 2, entries 21, 22).
Highly deactivated aldehydes as well as hindered
aldehydes were also diacetylated in excellent yields under
similar reaction conditions (Table 2, entries 3, 8-11).
Moreover, sensitive groups such as -OMe, -OCOPh,
thiophene ring, and TBDMS ethers are stable under the
described reaction conditions (Table 2, entries 9-13, 18-
20). It is also worth mentioning that ketones such as
acetophenone did not give any acylals with the above
catalyst even after 48 h (Table 2, entry 23). Therefore,
we also investigated the possible chemoselective protec-
tion of aldehydes in the presence of ketones. As shown
in Scheme 3, when a 1:1 mixture of benzaldehyde and
a
b
Isolated yields. GC yield. c No etherification product was
d
observed. No elimination product was detected.
(17) (a) Tomita, M.; Kikuchi, T.; Bessho, K.; Hori, T.; Inubushi, Y.
Chem. Pharm. Bull. 1963, 11, 1484. (b) Wegscheider, R.; Spath, E.
Monatsh. Chem. 1909, 30, 825.
of LiOTf (0.3 equiv) without any dimerization (Table 1,
entry 17). Interestingly, hindered tertiary alcohols such
as 1-methylcyclohexanol and adamantanol were also
converted to the corresponding acetates in excellent
yields (entries 18, 19), without the formation of any
detectable elimination products (entry 19). The last two
observations are undoubtedly due to the neutral feature
of LiOTf in our described protocol (Table 1, entries 17,
19).
1,1-Diacetates, on the other hand, are ambident sub-
strates containing two types of reactive carbon centers,
the carbon atom of the protected aldehyde function and
the carbonyl group in the ester moieties.15 The relative
acid stability of 1,1-diacetates is another interesting
feature of such 1,1-diacetates in the field of protection-
deprotection chemistry.16 1,1-Diacetates are also syn-
(18) Freeman, I.; Karchefski, E. M. J . Chem. Eng. Data 1977, 22,
355.
(19) Scriabire, I. Bull. Chem. Soc. Fr. 1961, 1194.
(20) Michie, J . K.; Miller, J . A. Synthesis 1981, 824.
(21) Deka, N.; Kalita, D. J .; Borah, R.; Sarma, J . C. J . Org. Chem.
1997, 62, 1563.
(22) Aggarwal, V. K.; Fonquerna, S.; Vennall, G. P. Synlett 1998,
849.
(23) Karimi, B.; Seradj, H.; Ebrahimian, G. R. Synlett 2000, 623.
(24) Olah, G. A.; Mehrotra, A. K. Synthesis 1982, 962.
(25) (a) Pereira, C.; Gigante, B.; Marcelo-Curto, M. J .; Carreyre, H.;
Perot, G.; Guisnet, M. Synthesis 1995, 1077. (b) Kumar, P.; Hegda, V.
R.; Kumar, T. P. Tetrahedron Lett. 1995, 36, 601.
(26) (a) Zhang, Z. H.; Li, T. S.; Fu, C. G. J . Chem. Res., Synop. 1997,
174. (b) Li, T. S.; Zhang, Z. H.; Gao, Y. J . Synth. Commun. 1998, 28,
4665.
(27) Sumida, N.; Nishioka, K.; Sato, T. Synlett 2001, 1921.
(28) (a) McKillop, A.; Ford, M. E. Tetrahedron 1974, 30, 2467. (b)
Hilborn, J . W.; MacKnight, E.; Picock, J . A.; Wedge, P. J . J . Am. Chem.
Soc. 1994, 116, 3337. (c) Cervinka, O.; Karel, B.; Oldrich, S. Collect.
Czech. Chem. Commun. 1973, 441. (d) Perine, T. D.; White, W. C. J .
Am. Chem. Soc. 1947, 69, 1542. (e) Tsuji, J .; Tsuruoka, K.; Yamamoto,
K. Bull. Chem. Soc. J pn. 1976, 49, 1701. (f) The Aldrich Library of 13
C
(15) Sandberg, M.; Sydnes, L. K. Tetrahedron Lett. 1998, 39, 6361
and references therein.
(16) Kochhar, K. S.; Bal, B. S.; Deshpande, R. P.; Rajadhyaksha, S.
N.; Pinnick, H. W. J . Org. Chem. 1983, 48, 1765.
and 1H FT NMR Spectra 1; Aldrich Chemical Co.: Milwaukee, WI; p
209A. (g) Grob, C. A.; Sawlewicz, P. Helv. Chim Acta 1988, 71, 1508.
(h) Dictionary of Organic Compounds, 6th ed.; Chapman & Hall: New
York, 1996.
4952 J . Org. Chem., Vol. 68, No. 12, 2003

TABLE 2. Acetyla tion of Ald eh yd es Usin g Ac2O in th e
P r esen ce of LiOTf a t Room Tem p er a tu r e
of the solvent under reduced pressure gave the almost pure
acetates. Further purification of products was achieved by
column chromatography to afford pure acetate(s) (Table 1).
Gen er a l P r oced u r e for th e P r ep a r a tion of 1,1-Dia c-
eta tes. To a magnetically stirred solution of aldehyde (2 mmol)
and freshly distilled acetic anhydride (5-8 mmol) was added
LiOTf (0.4 mmol) at room temperature, and the mixture was
stirred until complete disappearance of starting material (as
monitored by TLC). After completion, the reaction was quenched
with water (25 mL), and the mixture was extracted with CH2-
Cl2 (2 × 30 mL). The aqueous layer was separated and could be
evaporated under reduced pressure to afford the crude recycled
catalyst. The organic layer was separated, washed with satu-
rated NaHCO3 (2 × 25 mL) and water (15 mL), and dried over
anhydrous Na2SO4. Evaporation of the solvent under reduced
pressure gave the almost pure 1,1-diacetate. Further purification
using column chromatography gave the corresponding pure
product (Table 2).
substrate/
Ac2O/LiOTf
time yielda
entry
R1
R2
(h)
(%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Ph
Ph
H
1:5:0.0
1:5:0.2
1:6:0.2
1:8:0.2
1:5:0.2
1:5:0.2
1:5:0.2
1:8:0.2
1:8:0.2
1:8:0.2
1:8:0.2
1:8:0.2
1:8:0.2
1:6:0.2
1:6:0.2
1:6:0.2
1:8:0.2
1:8:0.2
1:8:0.2
1:8:0.2
1:5:0.2
1:5:0.2
1:8:0.2
24
12
14
19
12
12
12
20
29
22
36
16
21
12
15
16
17
31
26
21
23
25
48
11b
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
9621
96
3-(Br)C6H4
2,6-(Cl)2C6H3
4-(Me)C6H4
3-(Me)C6H4
4-(i-Pr)C6H4
2,4,6-(Me)3C6H2
4-(MeO)C6H4
3-(MeO)C6H4
2,5-(MeO)2C6H3
4-(PhCO2)C6H4
4-(MeS)C6H4
3-(NO2)C6H4
4-(NO2)C6H4
2-(NO2)C6H4
2-naphthyl
95
9520
93
95
89
9121
95
90
89
93
9326a
9421
9026b
8625a
8725a
91
Recover y of th e Ca ta lyst LiOTf fr om Th ese Rea ction s.
The aqueous layer was separated in the first stage of the above
workup procedure and could be evaporated under reduced
pressure to afford the crude recycled catalyst. After evaporation
of water, the resulting solid residue was recrystalized in CH3-
CN to give the corresponding pure LiOTf in 90-91% recovery
after drying at 110 °C for 12 h.
2-thenyl
4-(TBDMSO)C6H4
3-(TBDMSO)C6H4
n-propyl
CH3CHdCH
Ph
96
9021
9221
nr
1
2-Cycloh exyleth yl Aceta te. H NMR (500 MHz, CDCl3, 25
°C, TMS): δ 3.95-3.98 (t, J ) 6.9 Hz, 2H), 1.90 (s, 3H), 1.51-
1.60 (m, [4 + 1]H), 1.37-1.42 (m, 2H), 1.24 (m, 1H), 1.04-1.13
(m, 3H), 0.79-0.84 (m, 2H). 13C NMR (125 MHz, CDCl3, 25 °C,
TMS): δ 170.73, 62.52, 35.95, 34.50, 33.10, 26.41, 26.12, 20.77.
4-i-P r op ylben zyl Aceta te. 1H NMR (500 MHz, CDCl3, 25
°C, TMS): δ 7.45-7.47 (d, J ) 7.4 Hz, 2H), 7.35-7.37 (d, J )
7.4 Hz, 2H), 4.83 (s, 2H), 2.85-2.90 (septet, J ) 7.1 Hz, 1H),
2.01 (s, 3H), 1.27-1.29 (d, J ) 7.1 Hz, 6H). 13C NMR (125 MHz,
CDCl3, 25 °C, TMS): δ 171.02, 151.24, 136.10, 127.32, 126.59,
72.47, 34.55, 24.85, 20.11.
a
b
Isolated yields. GC yield.
SCHEME 3
1,1-Dia cetoxy-1-(4-ben xoyloxyp h en yl)m eth a n e. 1H NMR
(500 MHz, CDCl3, 25 °C, TMS): δ 8.19-8.21 (d, J ) 8.4 Hz,
2H), 7.73 (s, 1H), 7.64-7.67 (tt, J ) 7.50, 1 Hz, 1H), 7.59-7.61
(d, J ) 8.4 Hz, 2H), 7.50-7.53 (t, J ) 7.50 Hz, 2H), 7.27-7.28
(d, J ) 8.4 Hz, 2H), 2.13 (s, 3H). 13C NMR (125 MHz, CDCl3, 25
°C, TMS): δ 168.75, 164.96,152.01, 134.07, 133.27, 131.30,
130.26, 128.68, 128.18, 122.03, 89.09, 20.88.
acetophenone was allowed to react with acetic anhydride
(5.0 equiv) in the presence of LiOTf (0.2 equiv) and the
reaction mixture was worked up after 12 h, NMR
analysis of the crude products consisted of a 1:1 mixture
of benzaldehyde diacetyl acetal and acetophenone. How-
ever, unfortunately both aliphatic and aromatic alde-
hydes showed similar reactivity and, in our system, no
chemoselectivity was observed.
In continuation of our studies, we interestingly found,
for the first time, that LiOTf can be effectively recovered
from the reaction mixture during the workup procedure
by a simple evaporation of the aqueous phase and
subsequent recrystallization of the solid residues. The
percent of recovery in most cases was more than 90%
without any changes in the Lewis acid properties. This
undoubtedly renders the above protocol relatively envi-
ronmentally acceptable and makes LiOTf a strictly
neutral and recoverable Lewis acid in organic synthesis.
Further application of LiOTf and the other neutral
catalysts are currently ongoing in our laboratories.
1,1-Diacetoxy-1-(2,5-dim eth oxyph en yl)m eth an e. 1H NMR
(500 MHz, CDCl3, 25 °C, TMS): δ 7.98 (s, 1H), 7.04-7.05 (d, J
) 3.0 Hz, 1H), 6.87-6.89 (dd, J ) 9.0 Hz, 3.0 Hz, 1H), 6.82-
6.84 (d, J ) 9.0 Hz, 1H), 3.79 (s, 3H), 3.77 (s, 3H), 2.10 (s, 6H).
13C NMR (125 MHz, CDCl3, 25 °C, TMS): δ 168.51, 153.68,
151.34, 124.96, 115.49, 113.15, 112.51, 85.61, 56.41, 55.84, 20.83.
1,1-Dia cetoxy-1-(4-th iom eth ylp h en yl)m eth a n e. 1H NMR
(500 MHz, CDCl3, 25 °C, TMS): δ 7.61 (s, 1H), 7.39-7.41 (d,
J ) 8.3 Hz, 2H), 7.21-7.22 (d, J ) 8.3 Hz, 2H), 2.42 (s, 3H),
2.06 (s, 6H). 13C NMR (125 MHz, CDCl3, 25 °C, TMS): δ 168.70,
140.94,132.16,127.19, 126.17, 89.55, 20.80, 15.36.
1,1-Dia cetoxy-1-(2,6-d ich lor op h en yl)m eth a n e. 1H NMR
(500 MHz, CDCl3, 25 °C, TMS): δ 8.13 (s, 1H), 7.20-7.22 (d,
J ) 8.5 Hz), 7.12-7.16 (pseudo t, J ) 8.5 Hz), 1.98 (s, 6H). 13C
NMR (125 MHz, CDCl3, 25 °C, TMS): δ 166.24, 135.44, 131.14,
130.34, 129.35, 87.41, 20.38.
1,1-Dia cet oxy-1-(3-ter t-b u t yld im et h ylsilyloxyp h en yl)-
m eth a n e. 1H NMR (500 MHz, CDCl3, 25 °C, TMS): δ 7.59 (s,
1H), 7.17-7.20 (t, J ) 8.0 Hz, 1H), 7.05-7.07 (d, J ) 8.0 Hz,
1H), 6.95-6.96 (t, J ) 2.0 Hz, 1H), 6.80-6.83 (dd, J ) 8.0 Hz,
2.4 Hz), 2.04 (s, 6H), 0.96 (s, 9H), 0.18 (s, 6H). 13C NMR (125
MHz, CDCl3, 25 °C, TMS): δ 168.34, 155.78, 137.13, 129.65,
121.23, 119.56, 118.36, 89.40, 25.70, 20.63, 18.19, -4.43.
1,1-Dia cet oxy-1-(4-ter t-b u t yld im et h ylsilyloxyp h en yl)-
m eth a n e. 1H NMR (500 MHz, CDCl3, 25 °C, TMS): δ 7.59 (s,
1H), 7.01-7.05 (d, J ) 8.4 Hz, 2H), 6.68-6.73 (d, J ) 8.4 Hz,
2H), 1.95 (s, 6H), 0.92 (s, 9H), 0.18 (s, 6H). 13C NMR (125 MHz,
CDCl3, 25 °C, TMS): δ 168.55, 154.22, 132.68, 127.85, 124.38,
89.68, 23.59, 21.03, 18.21, -4.65.
Exp er im en ta l Section
Gen er a l P r oced u r e for Acetyla tion of Alcoh ols. To a
solution of alcohol (2 mmol) and acetic anhydride (5-8 mmol)
was added LiOTf (0.4-0.6 mmol) at room temperature, and the
mixture was stirred until complete disappearance of the starting
material (as monitored by TLC or GC). After completion, the
reaction was quenched with water (25 mL), and the mixture was
extracted with CH2Cl2 (2 × 30 mL). The organic layer was
separated, washed with saturated NaHCO3 (2 × 25 mL) and
water (15 mL), and dried over anhydrous Na2SO4. Evaporation
1,1-Dia cetoxy-1-(3-br om op h en yl)m eth a n e. 1H NMR (500
MHz, CDCl3, 25 °C, TMS): δ 7.58 (s, 1H), 7.55 (s, 1H), 7.33-
J . Org. Chem, Vol. 68, No. 12, 2003 4953

7.38 (dd, J ) 15.1 Hz, J ) 7.9 Hz, 2H), 7.11-7.14 (t, J ) 7.9
Hz), 1.98 (s, 6H). 13C NMR (125 MHz, CDCl3, 25 °C, TMS): δ
168.43, 137.89, 132.69, 130.43, 129.68, 125.50, 122.46, 88.66,
20.56.
(s, 9H), 2.11 (s, 6H). 13C NMR (125 MHz, CDCl3, 25 °C, TMS):
δ 168.63, 139.34, 137.76, 129.74, 128.88, 88.76, 20.92, 20.58,
19.87.
1,1-Diacetoxy-1-(3-m eth oxyph en yl)m eth an e. 1H NMR (500
MHz, CDCl3, 25 °C, TMS): δ 7.64 (s, 1H), 7.27-7.30 (t, J ) 7.9
Hz, 1H), 7.07-7.09 (d, J ) 7.9 Hz, 1H), 7.04 (s, 1H), 6.89-6.92
(dd, J ) 7.9 Hz, J ) 2.3 Hz, 1H), 3.78 (s, 3H), 2.09 (s, 6H). 13C
NMR(125 MHz, CDCl3, 25 °C, TMS): δ 168.72, 159.81, 137.01,
129.79, 118.93, 115.36, 112.22, 89.55, 55.30, 20.80.
Ack n ow led gm en t. The authors thank the Institute
for Advanced Studies in Basic Sciences (IASBS) Re-
search Council for support of this work. The authors also
thank the referees of the manuscripts for their helpful
and effective comments.
1,1-Diacetoxy-1-(4-i-pr opylph en yl)m eth an e. 1H NMR (500
MHz, CDCl3, 25 °C, TMS): δ 7.67 (s, 1H), 7.44-7.46 (d, J ) 8.0
Hz, 2H), 7.25-7.26 (d, J ) 8.0 Hz, 2H), 2.89-2.93 (septet, J )
6.9 Hz, 1H), 2.08 (s, 6H), 1.21-1.22 (d, J ) 6.9 Hz, 6H). 13C
NMR (125 MHz, CDCl3, 25 °C, TMS): δ 168.44, 150.54, 133.18,
126.81, 126.68, 89.83, 34.04, 23.92, 20.76.
Su p p or tin g In for m a tion Ava ila ble: NMR spectra for
selected compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
1,1-Diacetoxy-1-(2,4,6-tr im eth ylph en yl)m eth an e. 1H NMR
(500 MHz, CDCl3, 25 °C, TMS): δ 8.19 (s, 1H), 6.89 (s, 2H), 2.62
J O026678+
4954 J . Org. Chem., Vol. 68, No. 12, 2003