Aryliodine(III) diacetates as substrates for Pd-Ag catalyzed arylation of alkenes

Article abstract of DOI:10.1016/j.tetlet.2011.06.051

An unprecedented application of aryliodine(III) diacetates as substrates in Pd-Ag catalyzed arylation of alkenes is described. The mechanistic studies revealed that the binary Pd-Ag catalysis leads to the decomposition of aryliodine(III) diacetates to oxygen and aryl iodides followed by arylation of alkenes forming Heck-type products. Under optimized conditions both electron-rich and electron-deficient alkenes undergo arylation in high yields. Advantageously, the reaction proceeds smoothly in water as a solvent and neither organic ligands nor inert atmosphere are required.

Full text of DOI:10.1016/j.tetlet.2011.06.051

Tetrahedron Letters 52 (2011) 4327–4329
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Aryliodine(III) diacetates as substrates for Pd–Ag catalyzed arylation of alkenes
⇑
Nikolai M. Evdokimov, Alexander Kornienko, Igor V. Magedov
Department of Chemistry, New Mexico Institute of Mining and Technology, Socorro, NM 87801, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
An unprecedented application of aryliodine(III) diacetates as substrates in Pd–Ag catalyzed arylation of
alkenes is described. The mechanistic studies revealed that the binary Pd–Ag catalysis leads to the
decomposition of aryliodine(III) diacetates to oxygen and aryl iodides followed by arylation of alkenes
forming Heck-type products. Under optimized conditions both electron-rich and electron-deficient
alkenes undergo arylation in high yields. Advantageously, the reaction proceeds smoothly in water as
a solvent and neither organic ligands nor inert atmosphere are required.
Received 18 May 2011
Revised 7 June 2011
Accepted 10 June 2011
Available online 2 July 2011
Keywords:
Synthesis in water
Palladium
Ó 2011 Elsevier Ltd. All rights reserved.
Cross-coupling
Hypervalent iodine
The arylation of alkenes using Heck-type transformations is an
important method in organic synthesis.1 The exploration of the
scope of this process has revealed a number of possible leaving
groups that can be utilized in the aryl electrophile coupling partner
(Scheme 1).1,2
of the expected dimethoxycinnamyl acetate we isolated only
unsubstituted cinnamyl acetate (3a) in 68% (Scheme 3).
8
Clearly, allyl acetate underwent cross-coupling with PhI(OAc)2
and not dimethoxybenzene. A search of the literature revealed that
Reactions formally involving the use of ‘H’ as a leaving group,
so-called dehydrogenative or oxidative Heck transformations,
involve Pd(II) catalysis and require an oxidant to regenerate the
active Pd(II) species.2d,e The successful oxidizing agents utilized
in this process include Cu or Ag salts, benzoquinone, oxygen and
peroxides.2e Interestingly, ArI(OAc)2 reagents, widely used in many
palladium-catalyzed oxidative transformations,3,4 fail in Heck-type
reactions because of their propensity to oxidize olefins3,5 and we
are unaware of a single example of such chemistry. Herein, we re-
port that such an attempt to use ArI(OAc)2 reagents in an oxidative
Heck process resulted in an unprecedented reaction of ArI(OAc)2
with alkenes under Pd–Ag binary catalysis (Scheme 2). This finding
expands the scope of Heck chemistry by including the formal
‘I(OAc)2’ leaving group to the existing arsenal of Heck nucleofuges.
When this project was started, a direct arylation of allyl acetate
through the functionalization of an aromatic C–H bond was un-
known.6 In an attempt to accomplish such a transformation, we
used PhI(OAc)2 as an oxidizing agent and electron-rich 2,4-dime-
thoxybenzene to facilitate the oxidative electrophilic palladination
of an aromatic C–H bond. In addition, we added one half equivalent
of silver carbonate, whose proposed function was to stabilize the
intermediate aryl-cationic Pd-complex1,7 and to scavenge acetate
ions produced during PhI(OAc)2 reduction. Surprisingly, instead
Pd cat.
R
X
R
+
Ar
Ar
X = I, Br, Cl, OTf, COCl,1 ArI+BF4-,1 N2+BF4
SO2Cl,2a SO2Na,2b COOH,2c H,2d,e
,
-
1
Scheme 1.
Pd(OAc)2, Ag2CO3
I(OAc)2
R
R
+
Ar
Ar
CH3CN or H2O,
70oC, 8h
Scheme 2.
O
OAc
Pd(OAc)2 (5 mol%)
Ag2CO3 (0.5 equiv.)
O
0%
O
+
PhI(OAc)2 (1.1 equiv.)
CH3CN, 70oC, 8h
O
OAc
2a
1
OAc
68%
3a
⇑
Corresponding author. Tel.: +1 575 835 6886; fax: +1 575 835 5364.
E-mail address: imagedov@nmt.edu (I.V. Magedov).
Scheme 3.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.06.051

4328
N. M. Evdokimov et al. / Tetrahedron Letters 52 (2011) 4327–4329
Table 1
Table 2
Optimization of coupling of ArI(OAc)2 with allyl acetate
Optimization of coupling of ArI(OAc)2 with alkenes
I(OAc)2
Pd(OAc)2, TEMPO
0.5 equiv. Ag2CO3
0.5 equiv. CaCO3
I(OAc)2
R2
R2
Pd(OAc)2, Ag2CO3
TEMPO, base
CH3CN, 70oC, 8h
+
OAc
+
OAc
R1
R1
CH3CN, 70oC, 8h
1a
2a
3a
2a: R2 = CH2OAc
2b: R2 = COOCH3
2c: R2 = Ph
3b: R1 = H, R2 = COOCH3
3c: R1 = H, R2 = Ph
1a: R1 = H
1b: R1 = OCH3
Entry 1a
2a
Pd
Ag2CO3 TEMPO Equiv of
Yielda
(%)
3d: R1 = OCH3, R2 = CH2 OAc
3e: R1 = OCH3 , R2 = COOCH3
3f: R1 = OCH3, R2 = Ph
(equiv) (equiv) (equiv) (equiv) (equiv) base
1
2
3
4
5
1
1
1
1
1
1
0.05
0.05
0.05
0.05
0.05
1
1
1
1
1
0
0
0.1
0.2
0.1
None
None
None
None
50
52
64
58
22
1.1
1.1
1.1
1.1
Entry
1
2
Pd
TEMPO
Product Yielda
(%)
(equiv)
(equiv)
(equiv)
(equiv)
1
2
3
4
5
6
7
8
9
1.1
1
1
0.05
0.05
0.03
0.03
0.05
0.05
0.03
0.03
0.05
0.05
0.05
0.05
0.1
0.1
0.1
0
0
0
3b
3b
3b
3b
3b
3c
3c
3c
3c
3d
3e
3f
68
75
72
71
85
69
31
73
88
89
87
91
0.5 of
K2CO3
0.5 of
Cs2CO3
0.5 of
CaCO3
0.5 of
CaCO3
0.5 of
CaCO3
0.5 of
CaCO3
0.5 of
CaCO3
0.5 of
CaCO3
0.5 of
CaCO3
0.5 of
CaCO3
1.1
1.1
1.1
1.1
1.1
1.1
1
1
1
1.1
1
1
1
1
1
6
7
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1
1
1
1
1
1
1
1
1
0.05
0.05
0.05
0.05
0.05
0
1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
2
88
3
1
1.1
1.1
1.1
1.1
1
0
8
0
0.1
0.1
0.1
0.1
0
9
0.1
0.5
0.5
0.5
0.5
0.5
28
87
0
10
11
12
10
11
12
13
14b
1.1
a
Isolated by column chromatography.
0.01
0.03
0.03
5
Table 3
82
80
Decomposition of 4-methoxyphenyl (III) diacetate to iodoanisole
I(OAc)2
I
CD3CN, 70oC
a
Isolated by column chromatography.
Water was used as a solvent.
O
catalyst
O
b
1b
Entry Catalyst
% of
Time for the full
iodoanisolea conversionb (h)
this was a new transformation, presumably missed by the previous
investigators because ArI(OAc)2 is not commonly employed as an
oxidazing agent in these oxidative Heck transformations. Further-
more, it is known that under acidic conditions PhI(OAc)2 reacts
with arenes and olefins under Pd catalysis to give acetoxyarenes9
and vicinal diacetyldiols,10 respectively. Neither was detected in
our experiment conducted under basic conditions. Our optimiza-
tion experiments are shown in Table 1.
1
2
3
4
5
6
7
None
CaCO3
Ag2CO3
Pd(OAc)2
Pd(OAc)2 + CaCO3
Pd(OAc)2 + Ag2CO3
16
50
57
86
90
93
78
60
48
15
13
12
5
Pd(OAc)2 + CaCO3 + Ag2CO3 100
a
After 8 h, monitored by NMR.
Reactions conducted in sealed NMR tubes.
b
It was found (Table 1) that the reaction critically requires both
Pd and Ag catalysts; if either is omitted no product is obtained
(entries 8 and 11). In addition, base is important for the coupling,
indeed the highest yields were obtained with 0.5 equiv of CaCO3
(entries 7, 10, 13, and 14). Also, using TEMPO we were able to
improve the product yield (entries 2 and 3). The precise role of
TEMPO is not clear at this point, however, this reagent was re-
ported to improve reaction yields in oxidations of allylic alcohols
10 mol % excess of the alkene and no TEMPO (entry 5), whereas
the behavior of styrene was similar to that of allyl acetate, requir-
ing 10 mol % of TEMPO (entry 9). In addition, the reaction was suc-
cessful with 4-methoxyphenyliodine (III) diacetate12 (entry 10–12)
giving excellent product yields.
Sanford13a,b and Ritter13c have shown that ArI(OAc)2 are sub-
strates for Pd(II) oxidative insertion into I–O bond, forming Pd(IV)
or Pd(III) bimetallic species and aryliodide as a side product. Thus,
we studied the conversion of 4-methoxyphenyliodine(III) diacetate
into iodoanisole (Table 3). Indeed, we found that such decomposi-
tion14 is fastest when all our reaction components are present
(entry 7).
3
to unsaturated aldehydes by PhIðOAcÞ2 and in general is known
to facilitate various redox processes.11 Pleasingly, the reaction also
proceeded in high yield when water was used as a solvent
(entry 14).
The effects of electron properties of alkenes were explored next
(Table 2). The reactions of electron-deficient alkenes required
Ar
Ar-I(OAc)2
R
X2Pd(II)
CaCO3
AcOOAc
Pd(II), Ag (I)16
Ag(I)
1/2 O2
CO2
Ca(OAc)2
Ar-I
X2(OAc)2Pd(IV)
R
Scheme 4.

N. M. Evdokimov et al. / Tetrahedron Letters 52 (2011) 4327–4329
4329
OAc
I
1 equiv.
I(OAc)2
+
0.05 equiv. Pd(OAc)2
OAc
OAc
+
0.5 equiv. Ag2CO3
O
0.5 equiv. CaCO3
CH3CN, 70 oC, 8h
O
37%
33%
0.5 equiv.
0.5 equiv.
Scheme 5.
Additionally, we subjected this cross-coupling reaction (Table
1) to a thorough analysis by HPLC–MS and GC–MS. Trans-cinnamyl
acetate was detected as a major product along with the traces of 3-
phenylpropanaldehyde (product of b0-hydride elimination), phenyl
iodide (decomposition product), and cis-cinnamyl acetate. These
findings prompted us to propose a plausible mechanism for the
reaction (Scheme 4).
the reviewer of this manuscript for suggesting the experiment
shown in Scheme 5.
References and notes
1. Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100, 3009.
2. (a) Dubbaka, S. R.; Vogel, P. Angew. Chem., Int. Ed. 2005, 44, 7674; (b) Zhou, X.;
Luo, J.; Liu, J.; Peng, S.; Deng, G.-J. Org. Lett. 2011, 13, 1432; (c) Hu, P.; Kan, J.; Su,
W.; Hong, M. Org. Lett. 2009, 11, 2341; (d) Le Bras, J.; Muzart, J. Chem. Rev. 2011,
111, 1170; (e) Yeung, C. S.; Dong, V. M. Chem. Rev. 2011, 111, 1250. and
references cited therein.
The evolution of oxygen in stoichiometric quantities was con-
firmed by the indigo carmine and sodium dithionite methods.15
It is well known that aryliodine(III) compounds can be obtained
by oxidation of aryliodides with peroxy acids.12 Thus, the reverse
process involves decomposition of ArI(OAc)2 and generation of
AcOOAc and ArI. It is feasible that Pd catalyzes this reaction
through the formation of an unstable PdX2(OAc)2. Under basic con-
ditions AcOOAc undergoes Ag-catalyzed decomposition with the
production of O2. The in situ formed aryl iodide reacts with the al-
kene under these conditions as has been reported previously16 and
shown in a control experiment, in which 0.5 equiv of each
PhI(OAc)2 and 4-methoxyiodoanisole were used giving the equal
amounts of the respective cinnamyl acetates (Scheme 5).
In summary, we discovered a new alkene arylation reaction
with ArI(OAc)2. Since oxidative alkene arylations are commonly
achieved with diaryliodonium salts, which are in turn prepared17
from ArI(OAc)2, our process is synthetically more convenient. This
reaction does not involve the use of organic ligands or inert atmo-
sphere and can be performed in water as a solvent. Because of the
high yields, the purification of the products is advantageously sim-
ple and consists only of a short silica gel pad to separate inorganic
salts.18
3. Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2008, 108, 5299.
4. Deprez, N. R.; Sanford, M. S. Inorg. Chem. 2007, 46, 1924.
5. (a) Rodriguez, A.; Moran, W. J. Eur. J. Org. Chem. 2009, 1313; (b) Satterfield, A.
D.; Kubota, A.; Sanford, M. S. Org. Lett. 2011, 13, 1076.
6. Pan, D.; Yu, M.; Chen, M.; Jiao, N. Chem. Asian J. 2010, 5, 1090.
7. (a) Jeffery, T. Tetrahedron Lett. 1991, 32, 2121; (b) Su, Y.; Jiao, N. Org. Lett. 2009,
11, 2980; (c) Pan, D.; Jiao, N. Synlett 2010, 1577.
8. Notably, iodoaryl diacetates were used as reactants in catalyst-free Suzuki-type
coupling: (a) Yan, J.; Zhou, Z.; Zhu, M. Tetrahedron Lett. 2005, 46, 8173; and in a
domino carbopalladation/C–H activation/C–C bond forming process: (b) Tang,
S.; Peng, P.; Zhong, P.; Li, J.-H. J. Org. Chem. 2008, 73, 5476.
9. Yoneyama, T.; Crabtree, R. H. J. Mol. Catl. A: Chem. 1996, 108, 35.
10. Li, Yang; Song, D.; Dong, V. M. J. Am. Chem. Soc. 2008, 130, 2962.
11. Vogler, T.; Studer, A. Synthesis 2008, 1979.
12. Hossain, M. D.; Kitamura, T. J. Org. Chem. 2005, 70, 6984.
13. (a) Dick, A. R.; Kampf, J. W.; Sanford, M. S. J. Am. Chem. Soc. 2005, 127, 12790;
(b) Racowski, J.; Dick, A. R.; Sanford, M. S. J. Am. Chem. Soc. 2009, 131, 10974; (c)
Powers, D. C.; Geibel, M. A. L.; Klein, J. E. M. N.; Ritter, T. J. Am. Chem. Soc. 2009,
131, 17050.
14. About thermal decomposition of aryl iodine diacetates, see: Leffer, J. E.; Story,
L. J. J. Am. Chem. Soc. 1967, 89, 2333.
15. (a) Brotto, L.; Battistutta, F.; Tat, L.; Comuzzo, P.; Zironi, R. J. Agric. Food Chem.
2010, 58, 3567; (b) Tao, Z.; Goodisman, J.; Souid, A.-K. J. Phys. Chem. 2008, 112,
1511.
16. Pan, D.; Chen, A.; Su, Y.; Zhou, W.; Li, S.; Jia, W.; Xiao, J.; Liu, Q.; Zhang, L.; Jiao,
N. Angew. Chem., Int. Ed. 2008, 47, 4729.
17. Chen, D.-W.; Ochiai, M. J. Org. Chem. 1999, 64, 6804.
18. General Procedure. A suspension of 0.023 g of CaCO3 (0.225 mmol), 0.062 g of
Ag2CO3 (0.225 mmol), 0.007 g of TEMPO (0.045 mmol), 0.005 g of Pd(OAc)2
(0.0225 mmol), diacetyliodoarene (0.495 mmol) and 0.049 ml of allyl acetate
(0.45 mmol) was stirred in 3 mL of acetonitrile at 70 °C for 8 h. After that time
the solvent was evaporated under reduced pressure, the residue was
transferred in 1 mL of CHCl3 to silica gel column and eluted first with
hexanes (40 mL) and then with pure hexanes or EtOAc/hexanes (1/20) to yield
pure 3a–f.
Acknowledgments
This work is supported by the US National Institute of Health
(Grants RR-16480 and CA-135579) under the BRIN/INBRE and
AREA programs. Collaboration with Mass Spectroscopy Facility at
University of New Mexico is acknowledged. In addition, we thank