CO/C-H as an acylating reagent: A palladium-catalyzed aerobic oxidative carbonylative esterification of alcohols

Article abstract of DOI:10.1002/anie.201400612

A palladium-catalyzed oxidative carbonylative esterification of a variety of functionalized alcohols under base- and ligand-free conditions has been demonstrated. A CO/olefin combination was utilized as the acylating reagent with O₂ as a benign oxidant. Notably, the scope of the substrate alcohols has been greatly broadened. New choice: A palladium-catalyzed oxidative carbonylative esterification of a variety of functionalized alcohols under base- and ligand-free conditions is demonstrated, and a CO/olefin combination is utilized as the acylating reagent with O₂ as a benign oxidant. Notably, scope of the substrate alcohols has been greatly broadened.

Full text of DOI:10.1002/anie.201400612

Angewandte
Chemie
DOI: 10.1002/anie.201400612
Synthetic Methods
CO/C-H as an Acylating Reagent: A Palladium-Catalyzed Aerobic
Oxidative Carbonylative Esterification of Alcohols**
Lu Wang, Yanxia Wang, Chao Liu,* and Aiwen Lei*
Abstract:
A
palladium-catalyzed oxidative carbonylative
alcohols with O2 as the terminal oxidant.[7] In almost all of
those reactions, the attention was mainly focused on the
esterification of a variety of functionalized alcohols under
base- and ligand-free conditions has been demonstrated. ACO/
olefin combination was utilized as the acylating reagent with
O2 as a benign oxidant. Notably, the scope of the substrate
alcohols has been greatly broadened.
À
generality of R H reagents. Actually, from the point view of
the alcohol, CO/RH could be considered an ideal acylating
reagent for alcohol esterification. However, to the best of our
knowledge, of the reported oxidative carbonylative esterifi-
cations, alcohols were all utilized as the sacrificial reagents in
excess to enhance the reaction efficiency.[6e,7a,8] In many cases,
alcohols need to be used as the solvents. The main issue might
be related to the easy oxidation of alcohols under the reaction
conditions. Thus, substrate applicability of different kinds of
alcohols is greatly restricted. Herein, we demonstrate a palla-
dium-catalyzed aerobic oxidative carbonylative esterification
of alcohols to directly construct a,b-unsaturated esters under
base- and ligand-free conditions, wherein a CO/olefinic
system was utilized as the acylating reagent (Scheme 1).
Importantly, only stoichiometric amounts of the alcohol are
required, and the use of structurally complex alcohols is
allowed in this oxidative carbonylative esterification for the
synthesis of a,b-unsaturated esters.
E
sterification is a fundamental transformation in both
academic research and industrial chemistry as esters are
among the most important functional groups and are found
widely in fine chemicals, natural products, and polymers.[1]
Traditionally, esters are prepared by the reaction of alcohols
with activated acid derivatives such as acyl halides.[2] How-
ever, the corrosive and unstable properties of acyl halides and
the generation of unwanted byproducts make this process far
from satisfactory.
In recent years, transition-metal catalysis has emerged as
a powerful tool for promoting the esterification of alcohols.
Several new type of acylating reagents, such as aldehydes,[3]
have been used for the esterification of alcohols under
transition-metal catalysis. In the meantime, carbonylation has
recently been utilized to introduce a synthetically versatile
carbonyl group to various organic molecules in a very
efficient manner.[4] In this case, the CO/RX (organo electro-
philes) system was used as the acylating reagent for esterify-
ing alcohols through carbonlyative esterifcation.[5] As a result,
the electrophiles (RX) are mainly obtained from the pre-
Scheme 1. Palladium-catalyzed oxidative carbonylative esterification of
alcohols.
À
functionalization of the corresponding C H compounds, and
more and more attention has been paid to the direct oxidative
À
R H carbonylation process, in which CO/RH are utilized as
a,b-Unsaturated esters are important chemical feedstocks
and they not only exist in numerous biologically active
molecules and natural products (Scheme 2),[9] but also serve
as useful synthetic intermediates in organic synthesis.[10]
Therefore, there is a demand for developing a sustainable
the acylating reagents on account of the high atom and step
economy.[4a–c,6] O2 is considered an ideal terminal oxidant in
oxidative transformations and several reports have been
demonstrated in oxidative carbonylative esterification of
[*] L. Wang, Y. Wang, Dr. C. Liu, Prof. A. Lei
College of Chemistry and Molecular Sciences, Wuhan University
Wuhan 430072 (P. R. China)
E-mail: aiwenlei@whu.edu.cn
Homepage: http://aiwenlei.whu.edu.cn/
Prof. A. Lei
State Key Laboratory for Oxo Synthesis and Selective Oxidation,
Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences
Lanzhou 730000 (P. R. China)
[**] This work was supported by the 973 Program (2011CB808600), the
National Natural Science Foundation of China (21390400,
21025206, 21272180 and 21302148), and the Research Fund for the
Doctoral Program of Higher Education of China (20120141130002).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201400612.
Scheme 2. Selected examples of significant a,b-unsaturated esters
containing pharmaceuticals and natural products.
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Table 2: Palladum-catalyzed oxidative carbonylative esterification of
various alcohols 1 with 2a.[a]
and atom-economic method for the synthesis of a,b-unsatu-
rated esters.
We started our experiments by using benzyl alcohol (1a)
and 4-methylphenylene (2a) as the substrates in a ratio of 1:1.
After considerable effort, we found that a cosolvent system of
toluene and DMSO was appropriate. In the presence of PdCl2
(3 mol%), and Cu(OAc)2·H2O (20 mol%) under an atmos-
phere of CO/O2 (1:7) at 808C for 14 hours, the desired
product 3aa was obtained in 80% yield (Table 1, entry 1).
Entry
1
3
Yield [%][b]
1
2
3
R=OMe (1b)
R=NO2 (1c)
R=F (1d)
3ba
3ca
3da
81
69
97
Table 1: Impact of reaction parameters on the efficiency of palladium
catalyzed oxidative carbonylation of 1a with 2a.[a]
4
5
(1e)
(1 f)
3ea
3 fa
83
85
Entry
[Pd]
[Cu]
Yield [%][b]
6
7
(1g)
(1h)
3ga
3ha
98
66
1
PdCl2
PdCl2
Pd(OAc)2
[PdCl2(PPh3)2]
PdCl2
PdCl2
PdCl2
PdCl2
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
–
CuCl2
CuBr2
Cu(OAc)2·H2O
80
88 (85)
76
2[c]
3
4
5
6
71
8
9
(1i)
(1j)
(1k)
3ia
3ja
3ka
91
94
64
n.d.
n.d.
n.d.
52
10
7
8[d]
11
12
13
(1l)
3la
57
80
79
[a] Reaction conditions: 1a (0.5 mmol), 2a (0.5 mmol), palladium salts
(0.015 mmol) and copper salts (0.1 mmol), CO/O2 =1:7 (1 atm),
toluene/DMSO=1.0 mL:0.1 mL, 808C, 14 h. [b] The yield was deter-
mined by GC analysis and calibrated using biphenyl as the internal
standard. [c] 20 h. The yield within parentheses is that of the isolated
product. [d] Toluene/DMF=1:0.1 mL. DMSO=dimethylsulfoxide,
n.d.=not detected.
(1m)
(1n)
3ma
3na
14
15[c]
(1o)
(1p)
3oa
3pa
50
89
[a] Reaction conditions: 1 (0.5 mmol), 2a (0.5 mmol), PdCl2
(0.015 mmol), Cu(OAc)2·H2O (0.1 mmol), CO/O2 =1:7 (1 atm), in
toluene (1 mL) and DMSO (0.1 mL) at 808C for 20 h. [b] Yield of isolated
product. [c] 1.0 mmol 2a was applied.
Prolonging the reaction time to 20 hours resulted in an
increased yield of 88% (85% upon isolation; Table 1,
entry 2). The yield of the desired product 3aa was decreased
slightly when PdCl2 was replaced by either [PdCl2(PPh3)2] or
Pd(OAc)2 (Table 1, entries 3 and 4). Product was not obtained
in the absence of Cu(OAc)2·H2O (Table 1, entry 5). Replacing
of Cu(OAc)2·H2O with CuCl2 or CuBr2 delivered no desired
product (Table 1, entries 6 and 7). The variation of the mixed
solvent to toluene/DMF also led to reduced efficiency in
terms of chemical yield (Table 1, entry 8). Notably, when
toluene was employed as the sole solvent, only 5% yield of
the desired product 3aa was obtained, and no benzaldehyde
was detected (see Figure 1a in the Supporting Information).
When toluene was replaced by DMSO, the yield of the
desired product increased to 11%, and the amount of alcohol
oxidation increased greatly to a 57% yield (see Figure 1b in
the Supporting Information). These results hihglighted the
significance of the cosolvent system.
Next, the substrate scope of various alcohols with 2a was
explored. Delightfully, the results in Table 2 demonstrated
a high degree of functional-group tolerance for the alcohols.
A series of a,b-unsaturated esters were obtained in good to
excellent yields. Various substituted aryl methanols bearing
electron-withdrawing groups, such as 4-NO2 (3ca), and
electron-donating groups, such as 4-OMe (3ba), were well
tolerated, thus giving the desired products in good yields. 3,5-
Dimethoxylphenylmethanol also proceeded to afford the
desired product 3ea (83%). Aryl methanols substituted with
halogens, such as F and Cl, could also be acylated to generate
the desired products in excellent yields (3da and 3 fa). Other
aromatic substrates such as the naphthyl 3ga and furyl 3ha
were well tolerated.
Notably, a variety of primary aliphatic alcohols were
tested and proved to be perfect coupling partners in this
oxidative carbonylative esterification, thus giving the corre-
sponding products in good to excellent yields (Table 2,
entries 8–12). In addition, different kinds of functional
groups such as chloro (3ja), carbonyl (3la), and even acetal
groups (3ma) were tolerated in this transformation. Allylic
alcohol derivatives also showed good reaction efficiency, thus
generating the target products in moderate to good yields
(Table 2, entries 13 and 14). For diol compounds such as 2,2-
dimethylpropane-1,3-diol, both of the hydroxy groups par-
ticipated in the oxidative carbonylative esterification to
afford the corresponding diester 3pa in good yield (Table 2,
entry 15). In the cases shown in entries 10, 11, and 14 of
Table 2, the relatively low yields are due to the incomplete
conversion of the starting materials, and might result from the
catalyst decay as palladium black was also observed.
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To further explore the applicability of alcohols, various
secondary alcohols were also investigated (Scheme 3). l-
Menthol and dehydroepiandrosterone (DHEA), which
widely exist in plants and animals, reacted smoothly with 2a
to provide the corresponding oxidative carbonylation prod-
ucts in good to excellent yields (3qa and 3ra). Ethyl lactate
was also compatibile, and the desired product 3sa was
obtained in 64% yield. The reaction of 2a with simple
benzylic and aliphatic secondary alcohols, such as 1-phenyl-
ethanol, isopropanol, and cyclohexanol also proceeded to
afford the desired a,b-unsaturated esters in good to excellent
yields (3ta, 3ua, and 3va).
Scheme 4. Palladium-catalyzed oxidative carbonylation reactions of
various alkenes with alcohols. Reaction conditions: 1 (0.5 mmol), 2
(0.5 mmol), PdCl2 (0.015 mmol), Cu(OAc)2·H2O (0.1 mmol), CO/
O2 =1:7 in (1 atm), toluene (1.0 mL) and DMSO (0.1 mL) at 808C for
20 h. Yield is that of isolated product.
Scheme 3. Palladium-catalyzed oxidative carbonylation reactions of
various secondary alcohols with 2a. Reaction conditions:
1 (0.5 mmol), 2a (0.5 mmol), PdCl2 (0.015 mmol), Cu(OAc)2·H2O
(0.1 mmol), CO/O2 =1:7 (1 atm), in toluene and DMSO (1:0.1) at
808C for 20 h. Yield is that of the isolated product. [a] 38 h.
Subsequently, we investigated the applicability of various
alkenes in this transformation, and the results are listed in
Scheme 4. Both electron-donating and electron-withdrawing
substituents on styrene were well-tolerated in this reaction
(3ab and 3ac). Styrenes with alkyl substituents, such as
methyl, afforded the desired product in good to excellent
yields (3aa, 3af). Notably, chloro or bromo substituents (p-Cl,
p-Br, and m-Br) were well tolerated and the corresponding
esters 3ad, 3ae, and 3ag were obtained in good yields. The
halide functionalities provide the possibility for further
functionalization on the phenyl ring of styrene. Furthermore,
butyl acrylate readily reacted with pentan-1-ol to get the
desired fumaric ester in 53% yield (3ih). The relatively low
yield is due to the incomplete conversion of the starting
materials.
This tranformation is believed to proceed by the catalytic
cycle shown in Scheme 5.[6e,8,11] Initially, an alkoxy palladium
intermediate B is generated from the reaction between 1 and
the PdII species A through an alcoholysis step. As the reaction
proceeds in the absence of base, the acetate ligand is believed
to promote this alcoholysis and HOAc is generated.[12] Then,
B undergoes CO insertion to generate C and then olefin
insertion generates the intermediate D. b-Hydride elimina-
tion of D affords the final product 3 and releases a palladium
hydride speices E which is oxidized by O2 and the copper
catalyst in the presence of HOAc to regenerate PdII and
Scheme 5. Proposed mechanism.
complete the catalytic cycle.[12b,13] H2O is believed to be the
final byproduct.
As mentioned above, the alcohol oxidation is usually
a problem under oxidative conditions. As shown in Scheme 5,
alcohol oxidation would normally result from the b-hydride
elimination of B, and is usually a facile process.[3a,12b,14]
However, in this transformation, alcohol oxidation did not
occur, and the product a,b-unsaturated esters were obtained
in high selectivity. Thus, current reaction conditions might
suppress the alcohol oxidation process. To test this hypothesis,
the following experiments were carried out (Scheme 6). In the
absence of CO and olefin under the standard reactoin
conditions, 1a was oxidized to give a 38% yield of benzalde-
hyde, and the starting material was predominantly unreacted
(Scheme 6). When CO or the olefin was added to the reaction
system, the amount of aldehyde was reduced (Scheme 6b,c).
These results indicate that alcohol oxidation is sluggish under
the reaction conditions and either CO or the olefin could
suppress this oxidation step. Therefore, only one equivalent of
alcohol could be utilized in this transformation. It allows us to
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opoulos, C. Villalonga-Barber, Tetrahedron Lett. 2011, 52, 5319 –
5322; f) P. Li, J. Zhao, R. Lang, C. Xia, F. Li, Tetrahedron Lett.
2014, 55, 390 – 393; g) W.-J. Yoo, C.-J. Li, Tetrahedron Lett. 2007,
48, 1033 – 1035.
[4] a) Q. Liu, H. Zhang, A. Lei, Angew. Chem. 2011, 123, 10978 –
10989; Angew. Chem. Int. Ed. 2011, 50, 10788 – 10799; b) X. F.
Wu, H. Neumann, M. Beller, Chem. Soc. Rev. 2011, 40, 4986 –
5009; c) B. Gabriele, R. Mancuso, G. Salerno, Eur. J. Org. Chem.
2012, 6825 – 6839; d) Q. Liu, G. Li, J. He, J. Liu, P. Li, A. Lei,
Angew. Chem. 2010, 122, 3443 – 3446; Angew. Chem. Int. Ed.
2010, 49, 3371 – 3374; e) Y. S. Zhao, L. Q. Jin, P. Li, A. Lei, J. Am.
Chem. Soc. 2008, 130, 9429 – 9433; f) C. Liu, L. Q. Jin, A. Lei,
Synlett 2010, 2527 – 2536.
Scheme 6. Oxidation of benzyl alcohol under different conditions. The
yield was determined by HPLC and calibrated using biphenyl as the
internal standard.
[5] a) A. Brennfꢀhrer, H. Neumann, M. Beller, Angew. Chem. 2009,
121, 4176 – 4196; Angew. Chem. Int. Ed. 2009, 48, 4114 – 4133;
b) W. Mꢁgerlein, A. F. Indolese, M. Beller, Angew. Chem. 2001,
113, 2940 – 2943; Angew. Chem. Int. Ed. 2001, 40, 2856 – 2859;
c) X.-F. Wu, H. Neumann, M. Beller, Chem. Eur. J. 2012, 18,
3831 – 3834; d) Y. Hu, J. Liu, Z. Lu, X. Luo, H. Zhang, Y. Lan, A.
Lei, J. Am. Chem. Soc. 2010, 132, 3153 – 3158; e) W. Mꢁgerlein,
M. Beller, A. F. Indolese, J. Mol. Catal. A 2000, 156, 213 – 221;
f) D. A. Watson, X. Fan, S. L. Buchwald, J. Org. Chem. 2008, 73,
7096 – 7101; g) R. H. Munday, J. R. Martinelli, S. L. Buchwald, J.
Am. Chem. Soc. 2008, 130, 2754 – 2755; h) J. Albaneze-Walker,
C. Bazaral, T. Leavey, P. G. Dormer, J. A. Murry, Org. Lett. 2004,
6, 2097 – 2100; i) D. C. Reeves, S. Rodriguez, H. Lee, N. Haddad,
D. Krishnamurthy, C. H. Senanayake, Org. Lett. 2011, 13, 2495 –
2497; j) J. McNulty, J. J. Nair, A. Robertson, Org. Lett. 2007, 9,
4575 – 4578; k) C. Cai, N. R. Rivera, J. Balsells, R. R. Sidler, J. C.
McWilliams, C. S. Shultz, Y. Sun, Org. Lett. 2006, 8, 5161 – 5164;
l) J. Liu, B. Liang, D. X. Shu, Y. H. Hu, Z. Yang, A. Lei,
Tetrahedron 2008, 64, 9581 – 9584.
[6] a) X. F. Wu, H. Neumann, M. Beller, ChemSusChem 2013, 6,
229 – 241; b) B. Gabriele, G. Salerno, M. Costa, Top. Organomet.
Chem. 2006, 18, 239 – 272; c) P. Xie, Y. Xie, B. Qian, H. Zhou, C.
Xia, H. Huang, J. Am. Chem. Soc. 2012, 134, 9902 – 9905; d) H.
Chen, C. Cai, X. Liu, X. Li, H. Jiang, Chem. Commun. 2011, 47,
12224 – 12226; e) G. Cometti, G. P. Chiusoli, J. Organomet.
Chem. 1979, 181, C14 – C16; f) R. Lang, J. Wu, L. Shi, C. Xia,
F. Li, Chem. Commun. 2011, 47, 12553 – 12555; g) R. Lang, L.
Shi, D. Li, C. Xia, F. Li, Org. Lett. 2012, 14, 4130 – 4133; h) B. Liu,
B.-F. Shi, Synlett 2013, 2274 – 2278.
use a variety of functionalized primary and secondary
alcohols in this oxidative carbonylative esterification.
In conclusion, we have demonstrated a palladium-cata-
lyzed oxidative carbonylative esterification of various func-
tionalized alcohols under base- and ligand-free conditions,
wherein a CO/olefin combination was utilized as the acylating
reagent with O2 as a benign oxidant. Notably, this reaction
exhibits a wide range of functional-group tolerance. Detailed
mechanistic studies and the synthetic application of this
methodology are currently ongoing in our laboratory.
Experimental Section
General procedure: PdCl2 (2.7 mg, 0.015 mmol) and Cu(OAc)2·H2O
(20 mg, 0.1 mmol) were added to a 25 mL schlenk tube equipped with
a magnetic stirred bar, and a balloon filled with CO/O2 (1:7, 1 atm)
was connected to the Schlenk tube through the side arm, and purged
three times. DMSO (0.1 mL), 1a (54 mg, 0.5 mmol), 2a (59 mg,
0.5 mmol), and toluene (1.0 mL) were then injected into the tube by
syringe. The reaction was then heated to 808C and stirred for 20 h.
Upon completion, the reaction was quenched by ethyl acetate. The
pure product was obtained by flash column chromatography on silica
gel (petroleum/ethyl acetate = 50:1). The product 3aa was isolated as
a white solid in 85% yield.1H NMR (400 MHz, CDCl3): d = 7.71 (d,
J = 16.0 Hz, 1H), 7.50–7.30 (m, 7H), 7.18 (d, J = 8.0 Hz, 2H), 6.44 (d,
J = 16.0 Hz, 1H), 5.25 (s, 2H), 2.37 ppm (s, 3H); 13C NMR (101 MHz,
CDCl3): d = 167.0, 145.2, 140.8, 136.1, 131.6, 129.6, 128.6, 128.2(4),
128.1 (9), 128.1, 116.7, 66.3, 21.5 ppm.
[7] a) H. Zhang, D. Liu, C. Chen, C. Liu, A. Lei, Chem. Eur. J. 2011,
17, 9581 – 9585; b) S. Luo, F. X. Luo, X. S. Zhang, Z. J. Shi,
Angew. Chem. 2013, 125, 10792 – 10795; Angew. Chem. Int. Ed.
2013, 52, 10598 – 10601.
[8] a) J. Tsuji, M. Morikawa, J. Kiji, J. Am. Chem. Soc. 1964, 86,
4851 – 4853; b) T. Yukawa, S. Tsutsumi, J. Org. Chem. 1969, 34,
738 – 740.
Received: January 20, 2014
Revised: March 5, 2014
Published online: April 16, 2014
[9] a) L. M. LeBlanc, A. F. Pare, J. Jean-Francois, M. J. Hebert,
M. E. Surette, M. Touaibia, Molecules 2012, 17, 14637 – 14650;
b) B. LLC, Natural Tropane Alkaloids: Cocaine, Scopolamine,
Atropine, Hyoscyamine, Catuabine, Ecgonine, Tropane Alkaloid,
Methylecgonine Cinnamate, General Books LLC 2010; c) R.
Fife, J. C. Maclaurin, J. H. Wright, Br. Med. J. 1960, 2, 1848 –
1850.
Keywords: alcohols · esterification · oxidation · palladium ·
synthetic methods
.
[1] J. Otera, Esterification: methods, reactions, and applications,
Wiley-VCH, Weinheim, 2003.
[10] a) T. Hayashi, K. Yamasaki, Chem. Rev. 2003, 103, 2829 – 2844;
b) T. Takahashi, M. Yoshimura, H. Suzuka, T. Maegawa, Y.
Sawama, Y. Monguchi, H. Sajiki, Tetrahedron 2012, 68, 8293 –
8299; c) C. Hedberg, A. Richter, Synthesis 2010, 2039 – 2042;
d) K. Inanaga, K. Takasu, M. Ihara, J. Am. Chem. Soc. 2005, 127,
3668 – 3669; e) X.-W. Yang, H.-Q. Liu, M.-H. Xu, G.-Q. Lin,
Tetrahedron: Asymmetry 2004, 15, 1915 – 1918; f) D. H. Ryu,
E. J. Corey, J. Am. Chem. Soc. 2003, 125, 6388 – 6390.
[2] R. C. Larock, Comprehensive Organic Transformations: Com-
prehensive Organic Transformations: A Guide to Functional
Group Preparations, Vol. 1, 2nd ed., Wiley, New York, 1999.
[3] a) C. Liu, S. Tang, L. Zheng, D. Liu, H. Zhang, A. Lei, Angew.
Chem. 2012, 124, 5760 – 5764; Angew. Chem. Int. Ed. 2012, 51,
5662 – 5666; b) A. S. K. Hashmi, C. Lothschꢀtz, M. Ackermann,
R. Doepp, S. Anantharaman, B. Marchetti, H. Bertagnolli, F.
Rominger, Chem. Eur. J. 2010, 16, 8012 – 8019; c) X.-F. Wu, C.
Darcel, Eur. J. Org. Chem. 2009, 1144 – 1147; d) C. Marsden, E.
Taarning, D. Hansen, L. Johansen, S. K. Klitgaard, K. Egeblad,
C. H. Christensen, Green Chem. 2008, 10, 168; e) G. A. Her-
[11] a) C. Bianchini, G. Mantovani, A. Meli, W. Oberhauser, P.
Bruggeller, T. Stampfl, J. Chem. Soc. Dalton Trans. 2001, 690 –
698; b) C. Bianchini, A. Meli, W. Oberhauser, S. Parisel, O. V.
5660 www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Angewandte
Chemie
Gusev, A. M. Kalꢂsin, N. V. Vologdin, F. M. Dolgushin, J. Mol.
Catal. A 2004, 224, 35 – 49.
[12] a) T. Nishimura, T. Onoue, K. Ohe, S. Uemura, J. Org. Chem.
1999, 64, 6750 – 6755; b) S. S. Stahl, Angew. Chem. 2004, 116,
3480 – 3501; Angew. Chem. Int. Ed. 2004, 43, 3400 – 3420.
[13] T. Hosokawa, S. Murahashi, Acc. Chem. Res. 1990, 23, 49 – 54.
[14] a) M. S. Sigman, D. R. Jensen, Acc. Chem. Res. 2006, 39, 221 –
229; b) T. Mallat, A. Baiker, Chem. Rev. 2004, 104, 3037 – 3058;
c) K. P. Peterson, R. C. Larock, J. Org. Chem. 1998, 63, 3185 –
3189; d) M. J. Schultz, M. S. Sigman, Tetrahedron 2006, 62, 8227 –
8241; e) L. Jin, X. Luo, A. Lei, Acta Chim. Sinica 2012, 70, 1538 –
1542.
Angew. Chem. Int. Ed. 2014, 53, 5657 –5661
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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