Palladium-catalyzed alkoxycarbonylation of aryl- and alkenyl-iodonium salts

Article abstract of DOI:10.1039/a800209f

The palladium-catalyzed carbonylation of diaryliodonium tetrafluoroborates and tosylates (toluene-p-sulfonates) in the presence of methanol and phenol afforded aromatic esters at room temperature under one atmosphere of carbon monoxide. However, carbonylation of diaryliodonium triflates and bromides in methanol afforded 4-iodophenyl-substituted methyl esters.

Full text of DOI:10.1039/a800209f

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Palladium-catalyzed alkoxycarbonylation of aryl- and alkenyl-
iodonium salts
Suk-Ku Kang,* Tokutaro Yamaguchi, Pil-Su Ho, Won-Yeob Kim and
Hyung-Chul Ryu
Department of Chemistry, Sung Kyun Kwan University, Natural Science Campus,
Suwon 440-746, Korea
The palladium-catalyzed carbonylation of diaryliodonium
tetrafluoroborates and tosylates (toluene-p-sulfonates) in
the presence of methanol and phenol afforded aromatic
esters at room temperature under one atmosphere of car-
bon monoxide. However, carbonylation of diaryliodonium
triflates and bromides in methanol afforded 4-iodophenyl-
substituted methyl esters.
Table
1
Palladium-catalyzed alkoxycarbonylation of hypervalent
iodine compounds
Iodonium Reaction
Time
(min) Product
Isolated
yield (%)
a
b
Entry salts
conditions
A
20
20
PhCO2Me
83
91
+
–
6
a
1
2
Ph2I BF4
1
a
B
PhCO2Ph
The carbonylation of aryl and vinyl halides or triflates cata-
lyzed by palladium complexes in the presence of alcohols and
phenols represents an important procedure for the synthesis of
7
a
MeO
MeO
CO2Me
A
B
A
B
30
30
30
30
88
92
89
91
+
–
1
p-MeOC6H4I BF4
a variety of aromatic and α,β-unsaturated esters. The carbon-
6b
Ph
ylation of aryl bromides and iodides usually can be carried out
with Pd(PPh ) Cl as a catalyst under one atmosphere of car-
2
CO Ph
2
a
3
2
2
7
b
bon monoxide in an alcoholic solution, such as n-butanol, in
CO2Me
the presence of triethylamine, diethylamine, or sodium acetate
I+ –OTs
Ph
S
S
3
4
2–4
S
6c
as base, at 100 ЊC or less, to provide esters. In the case of
methyl esters, the reaction is slow at atmospheric pressure at
the boiling point of methanol and therefore the reaction
3
4
a
CO2Ph
7
6
c
5
requires the use of a higher pressure of carbon monoxide. In
I+BF4–
CO2Me
CO2Ph
A
B
20
20
93
89
Ph
Ph
connection with our programs to utilize hypervalent iodine
Ph
d
6
compounds, we have found that the palladium-catalyzed car-
Ph
I
bonylation of hypervalent iodonium salts with methanol and
phenol as nucleophiles at room temperature and one atmos-
phere of carbon monoxide affords esters or 4-iodophenyl-
substituted esters depending on the counterions present
7
d
CO Me 62
2
8
+
Ph2I+ –OTf
[
eqn. (1)].
5
A
30
1
b
MeO2C
CO2Me 25
91
R1CO2Me(Ph) or
CO2Me(Ph)
Pd catalyst
(1)
9
8
+
–
R1I PhX
Ph
O
Ph
I
6
7
I
I
A
A
30
30
CO
MeOH
OTf OTf
R1 = aryl, alkenyl
X = BF4 , OTs, OTf, Br
(or PhOH)
–
–
–
–
5
8
+
9
72
13
p-MeOC6H4I –OTf
+
Ph
The results of the palladium-catalyzed carbonylation of
hypervalent iodine compounds are summarized in Table 1.
2
b
Methoxycarbonylation of diphenyliodonium tetrafluoroborate
I
OMe
OMe
29
7
1
a
was accomplished without using base in the presence of
p-MeC6H4I+ –OTf
Ph
10
+
methanol and Pd(OAc) (0.2 mol%) as a catalyst under mild
2
8
9
A
A
30
60
conditions to afford the methyl ester 6a with high catalytic
turnovers under one atmosphere pressure of CO and at room
temperature in 93% yield (entry 1, Method A). However,
carbonylation of 1a in the presence of phenol was carried
out in the presence of 1 equiv. of NaOH and PhOH in DMF to
provide the phenyl ester 7a (entry 1, Method B). In this
reaction, the presence of NaOH (1 equiv.) was crucial. For
MeO2C
52
76
2
c
6
b
+
–
PhI Br
C6H4-p-NO2
8
1
c
8
the p-methoxyphenyl(phenyl)iodonium tetrafluoroborate 2a,
a
All the reactions were run with iodonium salts (1 equiv.) in the pres-
ence of CO (1 atm). Reaction conditions A: Pd(OAc)2 (0.2 mol%),
MeOH (1.2 equiv.), CO, DMF, rt; B: Pd(OAc) (0.2 mol%), PhOH
1.2 equiv.), NaOH (1 equiv.), CO, DMF, rt. The yields are isolated
during carbonylation in the presence of methanol and phenol,
the p-methoxyphenyl group was transferred and p-methoxy-
benzoic acid esters 6b and 7b were obtained as the sole products
2
b
(
(
entry 2, Method A and B). By utilizing 2-thienyl(phenyl)-
yields.
9
iodonium tosylate 3a, 2-thienylcarboxylic acid ester 6c and 7c
were successfully afforded (entry 3). This methodology was also
applied to alkenyliodonium tetrafluoroborate 4 to provide
α,β-unsaturated ester 7d. Accordingly the iodonium salt 4 was
reacted with CO (1 atm) in the presence of methanol and
phenol to furnish α,β-unsaturated esters 6d and 7d in 93 and
89% yields, respectively (entry 4). Unexpectedly, when diphenyl-
7
J. Chem. Soc., Perkin Trans. 1, 1998
841

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1
0
iodonium triflate 1b instead of diphenyliodonium tetrafluoro-
borate 1a was used as the iodonium source, the only difference
being the different counterion, p-iodobenzoic acid methyl ester
In summary, Pd(OAc) (0.2 mol%)-catalyzed carbonylation
in the presence of methanol afforded aromatic methyl esters
with diaryliodonium tetrafluoroborates or tosylates and p-
iodophenyl-substituted esters with diaryliodonium triflates and
bromides depending on the counterions of the iodonium salts.
2
1
1
8
was obtained (62%) together with dimethyl terephthalate 9†
25%) as a minor product (entry 5). Utilizing Zefirov’s reagent
(
5
1
2
as hypervalent iodine compound, treatment of 5 with
CO in the presence of Pd(OAc) (0.2 mol%) and methanol
2
Experimental
afforded methyl p-iodobenzoate 8 in 91% yield (entry 6). For
10
the p-methoxyphenyl(phenyl)iodonium triflate 2b, methyl
p-iodobenzoate 8 (72%) was obtained as a major product
along with dimethyl terephthalate 9 (13%) (entry 7). In the
Preparation of methyl p-benzoate 8
To a stirred solution of Zefirov’s reagent [Ph(OTf)OI(OTf)Ph]
(800 mg, 1.67 mmol) in MeOH (10 ml) under one atmosphere
pressure of carbon monoxide at room temperature was added
Pd(OAc) , (0.75 mg, 0.2 mol%). The reaction mixture was
stirred at room temperature for 30 min and then extracted with
diethyl ether (30 ml × 3). The organic layer was dried over
10
case of p-tolyl(phenyl)iodonium triflate 2c, unexpected p-
iodoanisole 10‡ was isolated as a minor product and methyl p-
methoxybenzoate 6b was obtained as a major product (entry
2
8
). As indirect evidence of the incorporation of a mexthoxy
group (entry 8), when the same reaction was conducted in
PhOH, p-iodophenoxybenzene and the p-phenoxy ester were
produced.
anhydrous MgSO , and the solvent evaporated in vacuo. The
4
crude product was separated by SiO column chromatography
2
(eluting with EtOAc–hexanes 1:10, R = 0.50) to afford 8 (264
f
For the formation of the unusual methyl p-iodobenzoate with
mg, 91%); δ (400 MHz, CDCl ) 3.91 (s, 3 H), 7.74 (m, 2 H),
H
3
13
Ϫ1
iodonium triflate, it is presumed that the intermediate p-
iodophenylpalladium complexes A generated by oxidative add-
7.80 (m, 2 H); νmax(KBR)/cm 3057, 2987, 1726, 1269; m/z 262,
230, 127, 75 (base peak), 73.
0
ition of Pd species to the para-position of the phenyl group
would be subjected to methoxycarbonylation to give 8, which
was subjected to further carbonylation to provide 9. With
reagent 2c, the intermediate A generated would couple with
MeOH without incorporation of carbon monoxide to afford
p-iodoanisole 10 as an unexpected product along with ester 6b
after carbonylation (Scheme 1). As indirect evidence of the
Acknowledgements
Generous financial support by KOSEF-OCRC and the Minis-
try of Education (BSRI-97-3420) is gratefully acknowledged.
References
I
CO2Me
1 (a) H. M. Colguboun, D. J. Thompson and M. V. Twigg, in
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MeOH
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Pd0
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I
CO Me
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b-c
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Pd0
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5
K. V. Nikitin, N. P. Andryukhova, N. A. Bumagin and I. P.
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–
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6
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A
I
CO2Me
–
–
X = OTf, Br
CO
MeOH
1
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8 The p-methoxyphenyl(phenyl)iodonium tetrafluoroborate 2a was
prepared by adaptation of the procedure reported by M. Ochiai. See
reference 7.
OMe
OMe
1
0
6b
Scheme 1
7
intermediacy of 8 and 10, when readily available methyl p-
iodobenzoate 8 and p-iodoanisole 10 were treated with CO and
MeOH under the same conditions, the esters 9 and 6b were also
produced, respectively.
Finally, it is noteworthy that the reaction of iodonium brom-
ide 1c with carbon monoxide in methanol with Pd(OAc) (0.2
9
A. J. Margida and G. F. Koser, J. Org. Chem., 1984, 49, 3643.
0 T. Kitamura, J. Matsuyuki, K. Nagata, R. Furuki and H. Taniguchi,
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11 M. D. Hylarides, D. S. Wilbur, S. W. Hardley and A. R. Fritzberg,
1
14
2
mol%) as a catalyst under one atmosphere pressure of carbon
monoxide at room temperature afforded methyl p-iodobenzoate
J. Organomet. Chem., 1989, 367, 259.
1
1
2 R. T. Hembre, C. P. Scott and R. Norton, J. Org. Chem., 1987, 52,
8
as the sole product in 76% yield (entry 9).
3
650.
3 S.-K. Kang, H.-W. Lee, J.-S. Kim and S.-C. Choi, Tetrahedron Lett.,
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14 P. Kazmierczak and L. Skulski, Synthesis, 1995, 1027.
1
†
9: TLC; SiO , EtOAc–hexane 1:10, R = 0.29; δ (400 MHz, CDCl )
2 f H 3
Ϫ1
3
.95 (s, 6 H), 8.11 (s, 4 H); νmax(KBr)/cm 3057, 2986, 1733, 1266;
m/z 194, 193, 162 (base peak), 134, 102.
Paper 8/00209F
Received 6th January 1998
Accepted 13th January 1998
‡
3
1
10: TLC; SiO , EtOAc–hexane 1:10, R = 0.53; δ (400 MHz, CDCl )
2 f H 3
Ϫ1
.78 (s, 3 H), 6.68 (m, 2 H), 7.55 (m, 2 H); νmax(KBr)/cm 2985, 1374,
242; m/z 234, 233 (base peak), 218, 91, 62.
8
42
J. Chem. Soc., Perkin Trans. 1, 1998