Bismuth(III) salts as convenient and efficient catalysts for the selective acetylation and benzoylation of alcohols and phenols

Article abstract of DOI:10.1016/S0040-4020(01)00521-X

Efficient acetylation and benzoylation of alcohols and phenols with acetic and benzoic anhydrides have been carried out under catalysis of bismuth(III) salts including BiCl₃, Bi(TFA)₃ and Bi(OTf)₃. Selective acetylation and benzoylation of alcohols in the presence of phenols is an additional advantage of this procedure.

Full text of DOI:10.1016/S0040-4020(01)00521-X

TETRAHEDRON
Pergamon
Tetrahedron 57 *2001) 5851±5854
BismuthꢀIII) salts as convenient and ef®cient catalysts for the
selective acetylation and benzoylation of alcohols and phenols
Iraj Mohammadpoor-Baltork,p Hamid Aliyan and Ahmad Reza Khosropour
Department of Chemistry, Isfahan University, Isfahan 81744, Iran
Received 3 January 2001; revised 20 April 2001; accepted 10 May 2001
AbstractÐEf®cient acetylation and benzoylation of alcohols and phenols with acetic and benzoic anhydrides have been carried out under
catalysis of bismuth*III) salts including BiCl3, Bi*TFA)3 and Bi*OTf)3. Selective acetylation and benzoylation of alcohols in the presence of
phenols is an additional advantage of this procedure. q 2001 Elsevier Science Ltd. All rights reserved.
The protection of hydroxyl groups of alcohols and phenols
by the formation of esters is one of the most important and
widely used transformations in organic chemistry.1 Protec-
tion of such functional groups is often necessary during the
course of various transformations in a synthetic sequence,
especially in the construction of polyfunctional molecules
such as nucleosides, carbohydrates, steroids and natural
products. In general, acylations take place by treatment of
alcohols and phenols with acid anhydrides or acid chlorides
in the presence of tertiary amines such as triethylamine and
diacetates,25 and alcoholysis, hydrolysis and acetolysis of
epoxides.26 In continuation of our work on Bi*III) catalysis,
we now report a simple and ef®cient method for the
acetylation and benzoylation of alcohols and phenols
catalyzed by BiCl3, Bi*TFA)3 and Bi*OTf)3 *Scheme 1).
As shown in Table 1, primary and secondary alcohols and
phenols are acetylated with acetic anhydride in excellent
yields under catalysis of BiCl3, Bi*TFA)3 and Bi*OTf)3
*entries 1±23). Dihydroxyl compounds are converted into
the corresponding diacetates ef®ciently *entries 24±26).
Tertiary alcohols such as triphenylmethanol *entry 27)
remained unchanged when the reaction was catalyzed by
BiCl3 and Bi*TFA)3, but in the presence of Bi*OTf)3 the
corresponding acetate was obtained in 80% yield. However,
tert-butyl alcohol *entry 28) acetylated in excellent yield in
the presence of these catalysts.
pyridine.2
In
addition,
4-*dimethylamino)pyridine
*DMAP),3 N,N,N0,N0-tetramethylethylenediamine *TMEDA),4
tributylphosphine,5 iodine,6 p-toluenesulfonic acid,7
alumina,8 zinc chloride,9 cobalt chloride,10 montmorillonite
K-10 and KSF,11 scandium tri¯ate,12 sulfamic acid,13 indium
tri¯ate,14 copper tri¯ate,15 tantalum chloride,16 trimethyl-
silyl tri¯ate,17 magnesium bromide,18 bismuth tri¯ate,19
silica gel-supported sodium hydrogen sulfate,20 Pseudo-
monas cepacia PS lipase adsorbed on celite21 and twisted
amides22 have also been applied for the acylation of alcohols
and phenols. However, some of these methods are not
entirely satisfactory: triethylamine and pyridine have
unpleasant odors and are not so easy to remove; tributyl-
phosphine is an irritant which is highly ¯ammable and
expensive; indium and scandium tri¯ates are expensive
catalysts; magnesium bromide suffers from low yields of
the products and long reaction times. Therefore, introduc-
tion of new methods and catalysts for the preparation of
esters is still in demand.
In order to extend the scope of these catalysts further, the
benzoylation of alcohols and phenols with benzoic
anhydride, a less reactive anhydride, was also investigated.
The results of this investigation are shown in Table 2. Treat-
ment of a series of alcohols and phenols with benzoic
anhydride in the presence of catalytic amounts of BiCl3,
Bi*TFA)3 and Bi*OTf)3 provided the corresponding benzo-
ates in excellent yields *entries 1±23). Dihydroxyl
compounds such as catechol, resorcinol and hydroquinone
are transformed to their dibenzoates ef®ciently *entries
24±26). Tertiary alcohols such as triphenylmethanol and
tert-butyl alcohol remained intact or benzoylated in poor
yields *entries 27 and 28). The experimental results show
that Bi*OTf)3 is more reactive and works better than the two
The applications of bismuth compounds to organic transfor-
mations have been extensively investigated.19,23 Recently,
we introduced BiCl3 as an ef®cient catalyst for the
conversion of oxiranes to thiiranes,24 deprotection of 1,1-
Keywords: acylation; alcohols; phenols; catalysts; bismuth compounds.
Corresponding author. Tel.: 198-311-7932705; fax: 198-311-689732;
e-mail: imbaltork@ui.ac.ir
p
Scheme 1.
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020*01)00521-X

5852
I. Mohammadpoor-Baltork et al. / Tetrahedron 57 %2001) 5851±5854
Table 1. Acetylation of alcohols and phenols catalyzed by Bi*III) salts
Run
Substrate
Producta
Yield *%)b/Condition/Time *min)
Bi*TFA)3
BiCl3
98/rt/35
97/rt/60
Bi*OTf)3
1
2
3
4
5
6
7
8
Benzyl alcohol
Benzyl acetate
96/rt/60
98/rt/90
97/rt/90
95/rt/180
95/rt/120
90/rt/60
97/rt/60
95/rt/105
95/rt/60
85/rt/135
98/rt/60
99/rt/5
99/rt/5
98/rt/5
97/rt/5
98/rt/5
98/rt/5
98/rt/5
99/rt/5
99/rt/5
97/rt/5
99/rt/5
2-Methoxybenzyl alcohol
3-Methoxybenzyl alcohol
2-Nitrobenzyl alcohol
3-Nitrobenzyl alcohol
4-Nitrobenzyl alcohol
4-Chlorobenzyl alcohol
4-Bromobenzyl alcohol
Benzoin
2-Methoxybenzyl acetate
3-Methoxybenzyl acetate
2-Nitrobenzyl acetate
3-Nitrobenzyl acetate
4-Nitrobenzyl acetate
4-Chlorobenzyl acetate
4-Bromobenzyl acetate
Benzoin acetate
98/rt/55
94/rt/180
95/rt/75
95/rt/30
98/rt/50
90/rt/60
98/re¯ux/35
90/re¯ux/60
98/rt/60
9
10
Cinnamyl alcohol
2-Phenylethanol
Cinnamyl acetate
2-Phenylethyl acetate
11
121-Heptanol
1-Heptyl acetate
98/rt/45
98/rt/60
99/rt/5
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
1-Octanol
2-Octanol
Cyclohexanol
*2)-Methanol
Phenol
2-Nitrophenol
4-Nitrophenol
4-Methoxyphenol
4-Hydroxybenzaldehyde
a-Naphthol
b-Naphthol
Catechol
Resorcinol
1-Octyl acetate
2-Octyl acetate
Cyclohexyl acetate
*2)-Menthyl acetate
Phenyl acetate
2-Nitrophenyl acetate
4-Nitrophenyl acetate
4-Methoxyphenyl acetate
4-Acetoxybenzaldehyde
a-Naphthyl acetate
b-Naphthyl acetate
Benzene-1,2-diyl diacetate
Benzene-1,3-diyl diacetate
Benzene-1,4-diyl diacetate
Triphenylmethyl acetate
tert-Butyl acetate
97/rt/45
95/rt/20
94/rt/35
94/re¯ux/20
97/re¯ux/50
92/re¯ux/120
96/re¯ux/60
97/re¯ux/35
80/re¯ux/90
98/re¯ux/65
95/re¯ux/90
95/re¯ux/180
94/re¯ux/65
94/re¯ux/60
0/re¯ux/120
98/re¯ux/20
95/rt/60
93/rt/40
90/rt/60
93/rt/25
98/rt/5
99/rt/5
98/rt/15
95/rt/20
98/rt/5
94/rt/45
98/rt/5
98/rt/5
90/rt/60
99/rt/5
98/rt/5
97/rt/15
98/rt/10
95/rt/15
80/rt/35
98/rt/10
90/re¯ux/120
85/re¯ux/180
80/re¯ux/120
94/re¯ux/120
80/re¯ux/180
95/re¯ux/120
85/re¯ux/120
95/re¯ux/90
90/re¯ux/45
85/re¯ux/60
0/re¯ux/120
96/re¯ux/30
Hydroquinone
Triphenylmethanol
tert-Butyl alcohol
a
All products were identi®ed by comparison of their physical and spectral data with those of authentic samples.
Isolated yields.
b
Table 2. Benzoylation of alcohols and phenols catalyzed by Bi*III) salts
Run
Substrate
Producta
Yield *%)b/Time *min)
Bi*TFA)3
BiCl3
Bi*OTf)3
1
2
3
4
5
6
7
8
Benzyl alcohol
Benzyl benzoate
97/45
90/60
91/60
96/80
97/70
94/80
95/45
98/40
91/60
95/70
97/40
95/60
90/80
90/65
91/80
90/70
88/100
94/60
91/60
92/80
92/75
94/60
98/30
95/35
99/30
98/30
97/25
99/40
98/30
99/30
99/35
95/35
98/25
2-Methoxybenzyl alcohol
3-Methoxybenzyl alcohol
2-Nitrobenzyl alcohol
3-Nitrobenzyl alcohol
4-Nitrobenzyl alcohol
4-Chlorobenzyl alcohol
4-Bromobenzyl alcohol
Benzoin
2-Methoxybenzyl benzoate
3-Methoxybenzyl benzoate
2-Nitrobenzyl benzoate
3-Nitrobenzyl benzoate
4-Nitrobenzyl benzoate
4-Chlorobenzyl benzoate
4-Bromobenzyl benzoate
Benzoin benzoate
9
10
Cinnamyl alcohol
2-Phenylethanol
Cinnamyl benzoate
2-Phenylethyl benzoate
11
121-Heptanol
1-Heptyl benzoate
94/35
95/60
0
96/2
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
1-Octanol
2-Octanol
Cyclohexanol
*2)-Menthol
Phenol
2-Nitrophenol
4-Nitrophenol
4-Methoxyphenol
4-Hydroxybenzaldehyde
a-Naphthol
b-Naphthol
Catechol
Resorcinol
1-Octyl benzoate
2-Octyl benzoate
Cyclohexyl benzoate
*2)-Menthyl benzoate
Phenyl benzoate
2-Nitrophenyl benzoate
4-Nitrophenyl benzoate
4-Methoxyphenyl benzoate
4-Benzoyloxybenzaldehyde
a-Naphthyl benzoate
b-Naphthyl benzoate
Benzene-1,2-diyl dibenzoate
Benzene-1,3-diyl dibenzoate
Benzene-1,4-diyl dibenzoate
Triphenylmethyl benzoate
tert-Butyl benzoate
92/40
95/45
93/60
94/50
97/25
98/30
94/35
95/30
98/25
95/60
95/50
94/45
95/45
92/45
95/45
94/60
95/60
99/60
5/120
45/80
90/60
91/85
90/60
91/45
96/120
94/180
90/120
93/80
94/100
90/100
94/90
91/120
93/100
97/100
0/120
95/180
80/180
93/180
82/180
89/120
83/120
90/120
82/180
91/180
92/120
0/120
Hydroquinone
Triphenylmethanol
tert-Butyl alcohol
40/120
10/120
Reactions were performed in re¯uxing CH3CN.
All products were identi®ed by comparison of their physical and spectral data with those of authentic samples.
Isolated yields.
a
b

I. Mohammadpoor-Baltork et al. / Tetrahedron 57 %2001) 5851±5854
5853
Table 3. Competitive acetylation and benzoylation of alcohols and phenols catalyzed by Bi*III) salts

5854
I. Mohammadpoor-Baltork et al. / Tetrahedron 57 %2001) 5851±5854
other catalysts in terms of reaction times, temperature and
the yields of the products. It is also noteworthy that bismuth
tri¯ate is better when compared with indium and scandium
tri¯ates as it is easier to handle and less expensive.
Acknowledgements
We are thankful to the Isfahan University Research Council
for the partial support of this work.
In order to show the selectivity of the described method, we
have also investigated the competitive acetylation and
benzoylation of alcohols and phenols, and found that
alcohols were acetylated and benzoylated selectively in
the presence of phenols *Table 3). This may be considered
as a useful practical achievement in esteri®cation reactions.
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In conclusion, we have developed an ef®cient and excellent
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alcohols and phenols. In addition, high chemoselectivity,
mild reaction conditions, high reaction rates and easy
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To a solution of alcohol or phenol *1 mmol) and acetic
anhydride *1.5 equiv. for each hydroxyl group of alcohol
or phenol) in CH3CN *3 mL) was added the catalyst
*0.1 mmol of BiCl3, 0.05 mmol of Bi*TFA)3 and
0.01 mmol of Bi*OTf)3). The reaction mixture was stirred
at room temperature or under re¯ux conditions for the
appropriate time according to Table 1. The progress of the
reaction was followed by GLC or TLC. The solvent was
evaporated and ether *20 mL) was added. The reaction
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Evaporation of the solvent followed by chromatography
on a silica-gel plate or silica-gel column afforded the pure
acetate *Table 1).
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To a solution of alcohol or phenol *1 mmol) and benzoic
anhydride *1.5 equiv. for each hydroxyl group of alcohol or
phenol) in CH3CN *3 mL) was added the catalyst *0.1 mmol
of BiCl3, 0.05 mmol of Bi*TFA)3 and 0.01 mmol of
Bi*OTf)3). The reaction mixture was stirred under re¯ux
conditions for the appropriate time according to Table 2.
The progress of the reaction was followed by GLC or
TLC. The solvent was evaporated and ether *20 mL) was
added. The reaction mixture was washed with 5% aqueous
solution of NaHCO3, then with water, and dried with
Na2SO4. Evaporation of the solvent followed by chromato-
graphy on a silica-gel plate or silica-gel column afforded the
pure benzoate *Table 2).
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