Bismuth triflate-catalyzed fries rearrangement of aryl acetates

Article abstract of DOI:10.1055/s-2004-836025

Bismuth triflate was found to be an efficient catalyst in the Fries rearrangement of phenyl or 1-naphthyl acetates. Both reactions proceeded smoothly with a catalytic amount of bismuth triflate (10 mol%) to afford the corresponding hydroxyaryl ketone in moderate to good yields in most cases.

Full text of DOI:10.1055/s-2004-836025

2
794
LETTER
Bismuth Triflate-Catalyzed Fries Rearrangement of Aryl Acetates
B
T
ismuth Triflat
h
i
R
e
r
nt of
A
r
r
A
cetat
y
e
s
Ollevier,* Valerie Desyroy, Muhammad Asim, Marie-Christine Brochu
Département de Chimie, Université Laval, Québec (Québec), G1K 7P4, Canada
Fax +1(418)6567916; E-mail: thierry.ollevier@chm.ulaval.ca
Received 27 July 2004
at reflux (Table 1). Among various catalyst loadings test-
Abstract: Bismuth triflate was found to be an efficient catalyst in
the Fries rearrangement of phenyl or 1-naphthyl acetates. Both
reactions proceeded smoothly with a catalytic amount of bismuth
triflate (10 mol%) to afford the corresponding hydroxyaryl ketone
in moderate to good yields in most cases.
ed, 10 mol% of Bi(OTf) was found to give the expected
3
product 2a with the best yield (Table 1, entry 2). Clearly,
the optimal catalyst loading was 10 mol%, as the yield of
deacetylated product, 1-naphthol (3a), was minimized in
these conditions.12
Key words: Fries rearrangement, bismuth(III), Lewis acid, phenol,
hydroxyaryl ketone, green chemistry
Table 1 Bi(OTf) -Catalyzed Fries Rearrangement of 1-Naphthyl
3
Acetate
O
Hydroxyaryl ketones are versatile intermediates in the
synthesis of biologically active naphthoquinones, chal-
cones, and flavanones. Although Friedel–Crafts reactions
provide an efficient synthetic route for the preparation of
hydroxyaryl ketones by direct 2-acylation reactions of
phenols and 1-naphthols, the Fries rearrangement has
OH
O
OH
O
CH3
Bi(OTf)3
CH3
+
PhMe, 110 °C
1a
2a
3a
1
been reported to be the most efficient process. Both of
these reactions are usually carried out using stoichiomet- Entry
n Equiv
Bi(OTf)3
Time
(h)
Yield of 2a Yield of 3a
(%)a
(%)
a
ric amount of AlCl or strong acids. An excess of the acid
3
is often required, due to the quenching of the acid by the
reaction products. These corrosive reaction conditions
1
0.05
0.10
0.20
7
6
8
68
32
have led to severe side reactions and to environmental
problems. Lately, synthetic methodologies involving lan-
thanide triflates as catalysts for the Fries rearrangement
2
80
20
3
52
26
2
a
have been described. High catalytic activity, low toxicity,
Isolated yield.
moisture and air tolerance make use of lanthanide triflates
attractive catalysts. However, the high cost of these cata-
lysts limits their use. Clearly, there is a need for the devel-
opment of new cheap Lewis acids that can promote the
above reaction in a catalytic amount.
We hence further studied the scope and limitations of this
reaction with differently substituted naphthyl acetates.
Several examples of Bi(OTf) -catalyzed Fries rearrange-
3
ment of 4- or 5-substituted 1-naphthyl acetates 1 are sum-
Bismuth compounds have attracted recent attention due to marized in Table 2. The corresponding hydroxynaphthyl
3
their low toxicity, low cost, and good stability. Bis- ketones 2 are obtained in moderate to good yield with 10
muth(III) salts have been reported as catalysts for epoxide mol% of Bi(OTf) in toluene or nitroethane. Toluene can
3
4
5
6
opening, imine allylation, Mukaiyama-aldol reaction,
be replaced by nitroethane, which is an industrially com-
7
13
formation and deprotection of acetals, Friedel–Crafts re- patible solvent. Similar yields were indeed obtained
8
9
actions, Diels–Alder reactions, and intramolecular with the rearrangement of 1-naphthyl acetate and 4- or 5-
1
0
Sakurai cyclizations. Bi(OTf) is particularly attractive methoxy 1-naphthyl acetates (Table 2, entries 1–6). How-
3
because it is commercially available or can be easily pre- ever, nitroethane gave a decreased yield vs toluene of the
pared from commercially available starting materials.11
4-chloro derivative (Table 2, entries 7, 8). Surprisingly,
the reaction performed in nitroethane with the 4-acetoxy
derivative only led to decomposition (Table 2, entry 10).
Herein, we report an attractive method using bismuth(III)
triflate tetrahydrate as a catalyst for the Fries rearrange-
ment of aryl acetates. Hydroxyaryl ketones are obtained The same conditions applied to various phenyl acetates
efficiently in the presence of 10 mol% of Bi(OTf)3.
did not afford the corresponding rearranged products as
smoothly as in the naphthyl series. The Fries rearrange-
ment did not occur with phenyl acetate and only led to
traces of the expected product (Table 3, entry 1). The
reaction was efficient using electron-rich meta-substituted
phenyl acetates and the corresponding hydroxyphenyl
ketones 5b and 5c were obtained with moderate yields
Initially, we screened various quantities of catalyst for the
Fries rearrangement of 1-naphthyl acetate (1a) in toluene
SYNLETT 2004, No. 15, pp 2794–2796
0
7
.1
2
.2
0
0
4
Advanced online publication: 25.11.2004
DOI: 10.1055/s-2004-836025; Art ID: S07104ST
(
Table 3, entries 2 and 4). Using nitroethane instead of
©
Georg Thieme Verlag Stuttgart · New York

LETTER
Bismuth Triflate-Catalyzed Fries Rearrangement of Aryl Acetates
2795
Table 2 Bi(OTf) -Catalyzed Fries Rearrangement of Substituted 1-
Table 3 Bi(OTf) -Catalyzed Fries Rearrangement of Substituted
3
3
Naphthyl Acetates
Phenyl Acetates
O
O
O
CH3
OH
O
O
CH3
OH
O
10% Bi(OTf)3
10 % Bi(OTf)3
CH3
CH3
Solvent, 110 °C
Solvent, 110 °C
R
R
R1
R2
R1
R2
4
5
1
2
Entry
R
H
Solventa
Compound Yield of 5
Entry R1
R2
Solventa
Compound Yield of 2
(%)b
b
(
%)
1
2
3
4
5
6
PhMe
PhMe
EtNO2
5a
5b
5b
5c
5c
5d
5e
10c
61
12
72
50
13c
12
1
2
3
4
5
6
7
8
9
0
H
H
PhMe
EtNO2
PhMe
EtNO2
PhMe
EtNO2
PhMe
EtNO2
PhMe
EtNO2
2a
2a
2b
2b
2c
2c
2d
2d
2e
2e
80
84
71
81
65
66
82
41
64
m-CH3
m-CH3
H
H
H
OCH3
OCH3
H
m-OCH3
m-OCH3
p-OCH3
PhMe
EtNO2
EtNO2
PhMe
H
OCH3
OCH3
H
H
7
p-O CCH
2
3
Cl
a
Conditions: substituted phenyl acetate (1.00 equiv), Bi(OTf) ·4H O
3
2
H
Cl
(0.10 equiv), solvent, 110 °C, 6–33 h.
b
Isolated yield.
GC yield.
H
O CCH
c
2
3
1
H
O CCH
6c
2
3
a
Conditions: 4-/5-substituted naphthyl acetate (1.00 equiv),
Table 4 Bi(OTf) -Catalyzed ortho-Acylation of 1-Naphthol
3
Bi(OTf) ·4H O (0.10 equiv), solvent, 110 °C, 3–15 h.
Isolated yield.
GC yield.
3
2
b
c
OH
OH
O
cat. Bi(OTf)3
CH3COX
CH3
Solvent, 110 °C
toluene led to very poor yield or decomposition (Table 3,
entries 3 and 5). Para-substituted phenyl acetates only led
to rearranged products in low yields (Table 3, entries 6
and 7).
3a
2a
Entry Conditions
Solvent Time (h) Yield (%)a
Following recent reports of direct 2-acylation reactions of
1
0.10 equiv Bi(OTf)3,
PhMe/
MeNO2
5
25
14
69
57
74
1
4
phenols and 1-naphthols with Sc(OTf) and Hf(OTf) ,
1.10 equiv CH COCl
3
4
3
we compared the direct Friedel–Crafts ortho-acylation of
-naphthol with the Fries rearrangement of naphthyl ace-
2
0.10 equiv Bi(OTf)3,
PhMe
PhMe
1
1
.50 equiv (CH CO) O
3 2
tate. As seen from Table 4, our conditions are efficient us-
ing acetyl chloride or acetic anhydride as acylating agent.
The reaction is chemoselective in that only C-acylation is
observed. Although the precise mechanism has not been
elucidated, we suppose that the reaction occurs by forma-
tion of a Bi(III)–phenolate complex. However, O-acyla-
3
0.20 equiv Bi(OTf)3,
1
.50 equiv (CH CO) O
3 2
a
Isolated yield.
tion followed by Fries rearrangement cannot be ruled out proven to be effective for the direct ortho-acylation of 1-
as Bi(OTf) is a known catalyst for the acylation of alco- naphthol with acetyl chloride or acetic anhydride. Both
3
1
5
hols and phenols. Further investigations on the mecha- methods offer several advantages including mild reaction
nism of this transformation are in progress.
conditions, low quantity of the catalyst (10%), and no for-
mation of decomposition products. Because of its various
In summary, we have found that Bi(OTf) is an efficient
3
benefits, the Bi(OTf) protocol should find utility in the
catalyst for the Fries rearrangement of naphthyl acetates.
The reaction appeared to be more general for naphthyl
acetates as compared to phenyl acetates. An optimization
of the catalyst amount showed that the reaction works best
3
synthesis of biologically active compounds. Development
of other Bi(OTf) -catalyzed Fries rearrangements and re-
3
lated mechanistic studies will be reported in due course.
1
6
with a catalyst loading of 10 mol%. Bi(OTf) has also
3
Synlett 2004, No. 15, 2794–2796 © Thieme Stuttgart · New York

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796
T. Ollevier et al.
LETTER
Acknowledgment
(8) (a) For a review on bismuth chloride and bismuth triflate in
acylation reactions: Le Roux, C.; Dubac, J. Synlett 2002,
This work was financially supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC, Canada), the
Fonds Québécois de la Recherche sur la Nature et les Technologies
1
81. (b) Desmurs, J. R.; Labrouillère, M.; Le Roux, C.;
Gaspard, H.; Laporterie, A.; Dubac, J. Tetrahedron Lett.
997, 38, 8871. (c) Répichet, S.; Le Roux, C.; Dubac, J.;
1
(
FQRNT, Québec, Canada), the Canada Foundation for Innovation,
Desmurs, J. R. Eur. J. Org. Chem. 1998, 2743. (d) Laporte,
C.; Marquie, J.; Laporterie, A.; Desmurs, J. R.; Dubac, J. C.
R. Acad. Sci. II C 1999, 2, 455.
and Université Laval. M.-C. B. thanks NSERC for an undergraduate
student research award. We thank Sidech s.a. (Tilly, Belgium) for a
generous gift of Bi O .
2
3
(9) (a) Garrigues, B.; Oussaid, A. J. Organomet. Chem. 1999,
585, 253. (b) Laurent-Robert, H.; Garrigues, B.; Dubac, J.
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(
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1
characterized by IR and H NMR spectroscopy, and accord
exactly with those that have been previously reported in the
literature.
Synlett 2004, No. 15, 2794–2796 © Thieme Stuttgart · New York