Organocatalytic Radical Involved Oxidative Cross-Coupling of N-Hydroxyphthalimide with Benzylic and Allylic Hydrocarbons

Article abstract of DOI:10.1002/adsc.201500623

The cross-coupling reaction between N-hydroxyphthalimide and various benzylic and allylic hydrocarbons was realized through an organocatalytic radical-mediated process involving C(sp³)-O bond formation using tert-butyl hydroperoxide (t-BuOOH) as an oxidant and tetra-n-butylammonium iodide [(n-Bu]₄NI] as a catalyst, during which the phthalimide N-oxyl (PINO) radical and benzylic and allylic radicals were generated in situ and underwent the selective radical/radical cross-coupling reaction. This novel method provides a convenient metal-free approach to the synthesis of O-alkylated hydroxy imides under mild reaction conditions.

Full text of DOI:10.1002/adsc.201500623

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DOI: 10.1002/adsc.201500623
Organocatalytic Radical Involved Oxidative Cross-Coupling of
N-Hydroxyphthalimide with Benzylic and Allylic Hydrocarbons
a
a
a
a,b,
Longyang Dian, Sisi Wang, Daisy Zhang-Negrerie, and Yunfei Du *
a
Tianjin Key Laboratory for Modern Drug Delivery & High-Efficiency, School of Pharmaceutical Science and Technology,
Tianjin University, Tianjin 300072, Peopleꢀs Republic of China
Fax: (+86)-22-2740-4031; phone: (+86)-22-2740-4031; e-mail: duyunfeier@tju.edu.cn
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, Peopleꢀs Republic of
b
China
Received: June 29, 2015; Revised: September 17, 2015; Published online: November 25, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500623.
Abstract: The cross-coupling reaction between N-
hydroxyphthalimide and various benzylic and allylic
hydrocarbons was realized through an organocata-
Research in the past decades has revealed a highly
reactive, oxidative intermediate, namely, the phthal-
imide N-oxyl radical (PINO), in many N-hydroxyph-
thalimide (NHPI)-catalyzed organic reactions.
PINO has also been used as a coupling partner with
3
[6]
lytic radical-mediated process involving C(sp )ÀO
bond formation using tert-butyl hydroperoxide (t-
BuOOH) as an oxidant and tetra-n-butylammoni-
hydrocarbons to form various O-alkylated hydroxy
[7]
um iodide [(n-Bu] NI] as a catalyst, during which
imides, some of which are useful building blocks in
4
[8]
the phthalimide N-oxyl (PINO) radical and benzylic
and allylic radicals were generated in situ and un-
derwent the selective radical/radical cross-coupling
reaction. This novel method provides a convenient
metal-free approach to the synthesis of O-alkylated
hydroxy imides under mild reaction conditions.
organic synthesis. The first coupling reaction be-
tween PINO and an allylic radical was realized by
using Pb(OAc) , a heavy metal oxidant back in
4
[7a]
1964. However, the yield as well as the selectivity
of the reaction were poor. After that, sodium period-
ate in wet silica gel was reported to promote the gen-
eration of the PINO radical from NHPI which
showed its efficiency in the coupling reactions with
Keywords: CÀH functionalization; hydrocarbons;
metal-free conditions; oxidative cross-coupling; rad-
icals
[7c]
cyclohexene and cyclooctene
[Scheme 1, Eq. (1)].
In 2008, a copper-catalyzed direct CÀO bond forma-
tion between NHPI and some simple hydrocarbons
was developed with PIDA being used as the oxidant
for the generation of the PINO radical in situ from
[7d]
NHPI.
Besides, cerium(IV) ammonium nitrate
In modern organic synthesis, intensive studies have (CAN) was also reported to be used as an oxidant in
been focusing on identifying novel direct CÀH bond the cross-coupling reaction of NHPI with benzylic
[7e]
functionalization since this avoidss prefunctionaliza- compounds [Scheme 1, Eq. (2)].
tion of substrates therefore improves atom economy
However, in most of these existing radical involved
[
1]
and energy efficiency. Among the various CÀH cross-coupling approaches, the use of metallic oxi-
bond functionalization reactions, selective radical in- dants was inevitable. Concerning the environmental
volved coupling reactions have been widely utilized problems and health issues associated with heavy
[9]
owing to their high efficiency in forming new chemi- metal residues, the search of an environmentally
[
2]
cal bonds. However, the existing reports on such friendly oxidative system to realize such cross-cou-
cross-coupling reactions often require the participa- pling reactions via direct oxidation of alkyl CÀH
tion of transition metals as catalysts or oxidants serv- bonds is still in demand. In 2015, Li and co-workers
ing to stabilize the transient radical intermediates developed a PIDA-mediated oxidative cross-coupling
[
3]
generated during the reaction process.
Radical reaction between NHPI and benzylic CÀH bonds, in
3
cross-coupling reactions without the involvement of which the C(sp )ÀH oxidation was activated by a poly-
[
4]
[10]
transition metals have been rarely reported. In this fluorophenylamide group.
Herein, we describe an
[11]
regard, development of novel radical cross-coupling (n-Bu) NI/t-BuOOH-mediated, highly selective or-
4
reactions under metal-free conditions should there- ganocatalytic oxidative cross-coupling via the PINO
[
5]
fore be highly desirable.
radical, generated in situ from NHPI under mild reac-
3
836
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Organocatalytic Radical Involved Oxidative Cross-Coupling
[
a]
Table 1. Optimization of the reaction conditions.
[b]
Entry Oxidant
Catalyst (mol%) Solvent Yield
[
c]
1
2
3
4
5
6
7
8
9
1
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
none
(n-Bu) NI (10)
KI (10)
NaI (10)
EtOAc 30%
EtOAc 15%
EtOAc 20%
4
[
[
d]
d]
(n-Bu) NI (10)
DMF
ND
4
(n-Bu) NI (10)
DCE
PhCl
MeCN
MeCN
MeCN
MeCN
20%
42%
91%
90%
ND
4
(n-Bu) NI (10)
4
(n-Bu) NI (10)
4
(n-Bu) NI (20)
4
[
d]
(n-Bu) I (10)
4
[
d]
0
t-BuOOH
none
20%
[
a]
Reaction conditions: the mixture of 1a (0.5 mmol), 2a
2.5 mmol) and the oxidant (1.5 mmol) in solvent (2 mL)
(
was heated at 758C for 6 h unless otherwise stated.
All the yields are of isolated products after silica gel
chromatography
t-BuOOH=tert-butyl hydroperoxide, anhydrous unless
otherwise stated.
[
[
[
b]
c]
d]
The mixture was heated at 758C for 12 h.
in this reaction for forming the desired cross-coupling
Scheme 1. Different approaches for the cross-coupling reac- product 3a (Table 1, entries 9 and 10).
tions of NHPI with hydrocarbons via the PINO radical.
The optimization of reaction condition was fol-
lowed by a scope study of the method. These results
tion conditions, and a benzylic or allylic carbon radi- summarized in Scheme 2 show that a broad range of
cal, oxidized from benzylic or allylic hydrocarbon, in the substituted benzylic substrates all yielded the de-
forming an O-alkylated hydroxy imide as the cross- sired products in moderate to excellent yields irre-
coupling product [Scheme 1, Eq. (3)].
spective of whether the benzylic carbon was bonded
Recently, we reported an organocatalytic amination to highly electron-withdrawing acyl group(s) (1b–d),
reaction of alkyl ethers via the (n-Bu) NI/t-BuOOH- in a sterically disfavored environment (1e–f), or
4
[12]
mediated radical involved oxidative cross-coupling.
bonded to an aromatic ring substituted by mildly elec-
Based on this new finding, we took on the study of tron-donating methyl group(s) (1g–k), with a strongly
applying this strategy to see if it could facilitate the electron-donating methoxy group (1m), or with
selective radical involved cross-coupling reaction be- a slightly electron-withdrawing Cl group (1n). One
tween N-hydroxyphthalimide and hydrocarbons.
compelling advantage of this method is its high regio-
The study started out with ethylbenzene being selectivity – except for 1k which contains two un-
chosen as the alkyl substrate to react with NHPI. The equivalent benzylic carbons, only one mono-oxygenat-
initial trial produced the desired cross-coupling prod- ed coupling product was formed for all substrates,
uct 3a in 30% yield (Table 1, entry 1). Screening for with the coupling sites being specifically the benzylic
the optimal reaction conditions involved tests of other carbon and the oxygen atom at NHPI. An inseparable
catalysts, solvents, and fine-tuning the amount of the regioisomeric mixture of products 3k and 3k’ was ob-
oxidant. These results showed that other catalysts tained in a total yield of 53% (the ratio is about 5:1).
such as NaI, KI gave poorer yields (Table 1, entries 2
Building upon the successful results from the ben-
and 3), solvent MeCN was far better than any of the zylic hydrocarbons, we extended our investigations to
other four solvents, and gave the highest yield of the the alkene series. The results are listed in Table 2. As
desired product 3a of 91% (Table 1, entries 1, 4–7), predicted, the coupling products were prepared, with
and larger amounts of (n-Bu) NI (up to 20 mol%) vir- the same high regioselectivity between the allylic
4
tually had no influence on the yield (Table 1, entry 8). carbon and the oxygen atom at NHPI, all in satisfac-
Additional control experiments indicated that both tory yields. Substrate 4e, containing three unequiva-
(
n-Bu) NI and t-BuOOH played an indispensible role lent allylic carbons, yielded an inseparable regioiso-
4
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Scheme 2. Scope of benzylic substrates. Reaction conditions: 1a (0.5 mmol), 2 (2.5 mmol), (n-Bu) NI (10 mol%), anhydrous
4
t-BuOOH (1.5 mmol), 758C, MeCN (2 mL), sealed tube, unless otherwise stated. All the yields were of isolated products.
meric mixture of compounds 5e and 5e’ (the ratio is
We carried out several control experiments in order
about 3.8:1), with the Z-form of 5e’ not being formed. to explore the mechanism of this cross-coupling reac-
For a linear terminal alkene such as 1-hexene, the re- tion (Scheme 4). One control experiment showed that
action provided an isomerized cross-coupling product the desired product 3a was obtained in lower yields if
5
f as an inseparable Z/E mixture (the ratio of E/Z is the catalyst was removed or switched to KI or I , sug-
2
[13]
about 2.2:1). However, the reaction of allylbenzene gesting that the iodide anion played an important role
as well as safrole afforded the isomerized cross-cou- in the activation of t-BuOOH. However, based on the
pling products 5g and 5h in only the E-configuration. result of the control experiment of Scheme 4d, we
To our delight, safrole was successfully converted to tentatively propose that this process did not involve
5
h with the reactive moiety of the methylene ether the generation of the hypervalent iodine species as
[14]
being well tolerated.
It is worth mentioning that the cross-coupling prod-
ucts could be selectively deprotected to form the cor-
responding alcohols or the hydroxylamines, both are
useful synthetic building blocks in the construction of
the heterocyclic compounds or the pharmaceutical in-
[
15]
termediates.
For example, product 5g could be
readily converted to the allylic hydroxylamine 6a via
hydrazolysis or to cinnamic alcohol 6b through Zn-
mediated reduction (Scheme 3).
Scheme 3. Selective deprotection of product 5g.
3
838
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Organocatalytic Radical Involved Oxidative Cross-Coupling
[a]
Table 2. Scope of allylic compounds.
[
a]
Reaction conditions: 1a (0.5 mmol), 4 (2.5 mmol), (n-Bu) NI (10 mol%), anhydrous t-
4
BuOOH (1.5 mmol), 758C, MeCN (2 mL), sealed tube, unless otherwise stated. All the
yields are of isolated products.
Inseparable isomeric products, 5e:5e’=3.8:1.
Inseparable Z/E isomeric products, E:Z=2.2:1.
[
[
b]
b]
[12]
proposed before.
In addition, when TEMPO was tert-butylperoxy radical with the assistance of iodide
added to the reaction mixture, the cross-coupling anion. The generated radical subsequently abstracts H
product 3a was isolated in the yield ofonly 15%, from NHPI to afford the PINO radical, which then
which supported the radical nature of the reaction traps a benzylic or allylic H-atom from the corre-
[
16]
process.
sponding hydrocarbon to produce the (most stable)
On the basis of all the observations as well as previ- carbon radical. The generated NHPI molecules were
[
17]
ous literature reports, we propose a plausible mech- oxidized again to form the PINO radical for the next
anistic pathway. As shown in Scheme 5, initially, t- cycle of the reaction. Finally, the benzylic/allylic
BuOOH decomposes to generate the tert-butoxyl or carbon radical and the PINO radical underwent a radi-
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Longyang Dian et al.
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Scheme 5. Proposed possible mechanism.
3
the coupling sites being the allylic/benzylic C(sp )
atom and the oxygen atom of NHPI, and the method
is applicable to a broad range of substituted hydrocar-
bons.
Experimental Section
General Procedure for the Organocatalytic Radical
Involved Oxidative Cross-Coupling Reaction
To a mixture of hydrocarbon 2 or 4 (2.5 mmol) and (n-
Bu) NI (0.05 mmol, 18.3 mg) in MeCN (2 mL) were added
4
N-hydroxyphthalimide
BuOOH (1.5 mmol). The reaction mixture was stirred at
58C under an air atmosphere in a sealed tube and the pro-
1 (0.5 mmol) and anhydrous t-
7
Scheme 4. Control experiments to investigate the possible
mechanism. Reaction conditions: (0.5 mmol), 2a
2.5 mmol), catalyst and oxidant, MeCN (2 mL), the reac-
cess of the reaction was monitored by TLC. Upon comple-
tion, the reaction mixture was quenched with the addition
of saturated Na S O (10 mL), and then it was extracted
1
(
2
2
8
tion mixture was heated in a sealed tube at 758C for 12 h.
with EtOAc (3”30 mL). The combined organic layers were
washed with brine (20 mL) and dried with anhydrous
Na SO . Then the solvent was removed under vacuum and
the residue was purified by silica gel chromatography, using
a mixture of PE/EtOAc to afford the desired cross-coupling
product 3 or 5.
2
4
cal combination process and formed the cross-cou-
pling title product of an O-alkylated hydroximide.
In summary, we have demonstrated an (n-Bu) NI/
4
t-BuOOH-mediated novel organocatalytic radical in-
volved cross-coupling reaction. In this transformation,
3
the PINO radicals and sp carbon radicals were gener-
ated in situ and smoothly underwent the cross-cou-
pling reaction, in the absence of any transition metal,
Acknowledgements
providing the corresponding products in moderate to We acknowledge the National Natural Science Foundation of
excellent yields. The reaction is highly selective, with China (21472136) for financial support.
3
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Organocatalytic Radical Involved Oxidative Cross-Coupling
References
2013, 52, 5827–5831; f) Y.-F. Liang, X. Li, X. Wang, Y.
Yan, P. Feng, N. Jiao, ACS Catal. 2015, 5, 1956–1963.
[7] a) E. Lemaire, A. Rassat, Tetrahedron Lett. 1964, 5,
2245–2248; b) N. Koshino, B. Saha, J. H. Espenson, J.
Org. Chem. 2003, 68, 9364–9370; c) S. Coseri, Eur. J.
Org. Chem. 2007, 1725–1729; d) J. M. Lee, E. J. Park,
S. H. Cho, S. Chang, J. Am. Chem. Soc. 2008, 130,
7824–7825; e) A. O. Terent’ev, I. B. Krylov, M. Y. Shari-
pov, Z. M. Kazanskaya, G. I. Nikishin, Tetrahedron
2012, 68, 10263–10271; f) A. S. Patil, D.-L. Mo, H.-Y.
Wang, D. S. Mueller, L. L. Anderson, Angew. Chem.
2012, 124, 7919–7923; Angew. Chem. Int. Ed. 2012, 51,
7799–7803; g) B. Tan, N. Toda, C. F. Barbas III, Angew.
Chem. 2012, 124, 12706–12709; Angew. Chem. Int. Ed.
2012, 51, 12538–12541; h) X.-F. Xia, Z. Gu, W. Liu, H.
Wang, Y. Xia, H. Gao, X. Liu, Y.-M. Liang, J. Org.
Chem. 2015, 80, 290–295; i) R. Bag, D. Sar, T. Punniya-
murthy, Org. Lett. 2015, 17, 2010–2013.
[8] A. Alanine, A. Bourson, B. Büttelmann, R. Gill, M.-P.
Heitz, V. Mutel, E. Pinard, G. Trube, R. Wylera,
Bioorg. Med. Chem. Lett. 2003, 13, 3155–3159.
[9] a) S. L. Y. Tang, R. L. Smith, M. Poliakoff, Green
Chem. 2005, 7, 761–762; b) R. A. Sheldon, Chem. Soc.
Rev. 2012, 41, 1437–1451; c) K. Chen, P. Zhang, Y.
Wang, H. Li, Green Chem. 2014, 16, 2344–2744.
[1] For selected reviews, see: a) X. Chen, K. M. Engle, D.-
H. Wang, J.-Q. Yu, Angew. Chem. 2009, 121, 5196–
5217; Angew. Chem. Int. Ed. 2009, 48, 5094–5115;
b) C.-J. Li, Acc. Chem. Res. 2009, 42, 335–344; c) T. W.
Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147–1169;
d) L.-M. Xu, B.-J. Li, Z. Yang, Z.-J. Shi, Chem. Soc.
Rev. 2010, 39, 712–733; e) J. Wencel-Delord, T. Droge,
F. Liu, F. Glorius, Chem. Soc. Rev. 2011, 40, 4740–4761;
f) S. H. Cho, J. Y. Kim, J. Kwak, S. Chang, Chem. Soc.
Rev. 2011, 40, 5068–5083; g) L. Ackermann, Chem. Rev.
2011, 111, 1315–1345; h) S. R. Neufeldt, M. S. Sanford,
Acc. Chem. Res. 2012, 45, 936–946; i) K. M. Engle, T.-S.
Mei, M. Wasa, J.-Q. Yu, Acc. Chem. Res. 2012, 45, 788–
802; j) S. A. Girard, T. Knauber, C.-J. Li, Angew.
Chem. 2014, 126, 76–103; k) Angew. Chem. Int. Ed.
2
2
014, 53, 74–100; l) F. Jia, Z. Li, Org. Chem. Front.
014, 1, 194–214.
[
[
2] a) D. J. Hart, Science 1984, 223, 883–887; b) H. Fischer,
Chem. Rev. 2001, 101, 3581–3610; c) T. Pintauer, K.
Matyjaszewski, Chem. Soc. Rev. 2008, 37, 1087–1097.
3] a) M. T. Lemaire, Pure Appl. Chem. 2004, 76, 277–293;
b) R. Poli, Eur. J. Inorg. Chem. 2011, 1513–1530; c) C.
Liu, D. Liu, A. Lei, Acc. Chem. Res. 2014, 47, 3459–
3
470; d) L. Zhou, S. Tang, X. Qi, C. Lin, K. Liu, C. Liu,
[10] P. -C. Qian, Y. Liu, R.-J. Song, M. Hu, X.-H. Yang, J.-N.
Xiang, J.-H. Li, Eur. J. Org. Chem. 2015, 1680–1684.
[11] For selected reviews, see: a) D. Liu, A. Lei, Chem.
Asian J. 2015, 10, 806–823; b) P. Finkbeiner, B. J.
Nachtsheim, Synthesis 2013, 45, 979–999; c) M. Uyanik,
K. Ishihara, ChemCatChem. 2012, 4, 177–185. For se-
lected examples, see: d) M. Uyanik, H. Okamoto, T.
Yasui, K. Ishihara, Science 2010, 328, 1376–1379; e) L.
Chen, E. Shi, Z. Liu, S. Chen, W. Wei, H. Lei, K. Xu,
X. Wan, Chem. Eur. J. 2011, 17, 4085–4089; f) M.
Uyanik, D. Suzuki, T. Yasui, K. Ishihara, Angew.
Chem. 2011, 123, 5443–5446; Angew. Chem. Int. Ed.
2011, 50, 5331–5334; g) Z. Liu, J. Zhang, S. Chen, E.
Shi, Y. Xu, X. Wan, Angew. Chem. 2012, 124, 3285–
3289; Angew. Chem. Int. Ed. 2012, 51, 3231–3235; h) J.
Feng, S. Liang, S.-Y. Chen, J. Zhang, S.-S. Fu, X.-Q. Yu,
Adv. Synth. Catal. 2012, 354, 1287–1292; i) J. Huang, L.-
T. Li, H.-Y. Li, E. Husan, P. Wang, B. Wang, Chem.
Commun. 2012, 48, 10204–10206; j) G. Majji, S. Guin,
A. Gogoi, S. Kumar Rout, B. K. Patel, Chem. Commun.
2013, 49, 3031–3033; k) X.-F. Wu, J.-L. Gong, X. Qi,
Org. Biomol. Chem. 2014, 12, 5807–5817; l) H. Yu, J.
Shen, Org. Lett. 2014, 16, 3204–3207; m) S. Guo, J.-T.
Yu, Q. Dai, H. Yang, J. Cheng, Chem. Commun. 2014,
50, 6240–6242; n) M. Uyanik, H. Hayashi, K. Ishihara,
Science 2014, 345, 291–294; o) B. Mondal, S. C. Sahoo,
S. C. Pan, Eur. J. Org. Chem. 2015, 3135–3140; p) W.
Xu, B. J. Nachtsheim, Org. Lett. 2015, 17, 1585–1588;
q) M. Uyanik, D. Suzuki, M. Watanabe, H. Tanaka, K.
Furukawa, K. Ishihara, Chem. Lett. 2015, 44, 387–389.
[12] L. Dian, S. Wang, D. Zhang-Negrerie, Y. Du, K. Zhao,
Chem. Commun. 2014, 50, 11738–11741.
Y. Lan, A. Lei, Org. Lett. 2014, 16, 3404–3407; e) S.
Ghorpade, R.-S. Liu, Angew. Chem. 2014, 126, 13099–
13102; Angew. Chem. Int. Ed. 2014, 53, 12885–12888.
[
[
4] a) B. C. Giglio, V. A. Schmidt, E. J. Alexanian, J. Am.
Chem. Soc. 2011, 133, 13320–13322; b) V. A. Schmidt,
E. J. Alexanian, J. Am. Chem. Soc. 2011, 133, 11402–
11405; c) R. K. Quinn, V. A. Schmidta, E. J. Alexanian,
Chem. Sci. 2013, 4, 4030–4034; d) Q. Lu, J. Zhang, G.
Zhao, Y. Qi, H. Wang, A. Lei, J. Am. Chem. Soc. 2013,
135, 11481–11484.
5] In the past few decades, commercially available persis-
tent radical reagents such as TEMPO and other similar
nitroxides, often used as radical scavengers in radical
involved cross-coupling reactions, have been intensely
studied in many coupling reactions involving various C-
centered radicals, for reviews, see: a) E. G. Bagryan-
skaya, S. R. A. Marque, Chem. Rev. 2014, 114, 5011–
5056. For selected examples, see: b) H.-J. Kirner, F.
Schwarzenbach, P. A. v. d. Schaaf, A. Hafner, V. Rast,
M. Frey, P. Nesvadba, G. Rist, Adv. Synth. Catal. 2004,
346, 554–560; c) J. Sobek, R. Martschke, H. Fischer, J.
Am. Chem. Soc. 2001, 123, 2849–2857; d) J. Chateau-
neuf, J. Lusztyk, K. U. Ingold, J. Org. Chem. 1988, 53,
1629–1632; e) P. K. Kancharla, T. Kato, D. Crich, J.
Am. Chem. Soc. 2014, 136, 5472–5480; f) H. Liu, W.
Feng, C. W. Kee, Y. Zhao, D. Leow, Y. Pana, C.-H. Tan,
Green Chem. 2010, 12, 953–956.
[
6] For selected reviews, see: a) Y. Ishii, S. Sakaguchi, T.
Iwahama, Adv. Synth. Catal. 2001, 343, 393–427;
b) R. A. Sheldon, I. W. C. E. Arends, Adv. Synth. Catal.
2004, 346, 1051–1071; c) F. Recupero, C. Punta, Chem.
Rev. 2007, 107, 3800–3842; For selected examples, see:
d) T. Hara, T. Iwahama, S. Sakaguchi, Y. Ishii, J. Org.
Chem. 2001, 66, 6425–6431; e) Y. Yan, P. Feng, Q.-Z.
Zheng, Y.-F. Liang, J.-F. Lu, Y. Cui, N. Jiao, Angew.
Chem. 2013, 125, 5939–5943; Angew. Chem. Int. Ed.
[13] a) M. S. Chen, M. C. White, J. Am. Chem. Soc. 2004,
126, 1346–1347; b) S. A. Reedl, A. R. Mazzotti, M. C.
White, J. Am. Chem. Soc. 2009, 131, 11701–11706.
[14] S. K. Rout, S. Guin, W. Ali, A. Gogoi, B. K. Patel, Org.
Lett. 2014, 16, 3086–3089.
Adv. Synth. Catal. 2015, 357, 3836 – 3842
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
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Longyang Dian et al.
COMMUNICATIONS
[
15] a) B. Egart, D. Lentz, C. Czekelius, J. Org. Chem. 2013,
[16] The adduct product of TEMPO with ethylbenzene was
1
78, 2490–2499; b) T. Ishikawa, M. Kawakami, M.
detected in the crude H NMR and further confirmed
Fukui, A. Yamashita, J. Urano, S. Saito, J. Am. Chem.
Soc. 2001, 123, 7734–7735; c) H. Bian, J. Feng, M. Li,
W. Xu, Bioorg. Med. Chem. Lett. 2011, 21, 7025–7029;
d) Y. Zhang, L. Chen, T. Lua, Adv. Synth. Catal. 2011,
by comparison with the previously reported data in
ref.
[17] a) W.-P. Mai, H.-H. Wang, Z.-C. Li, J.-W. Yuan, Y.-M.
[
7d]
Xiao, L.-R. Yang, P. Mao, L.-B. Qu, Chem. Commun.
2
012, 48, 10117–10119; b) W. Wei, C. Zhang, Y. Xu,
353, 1055–1060.
X. B. Wan, Chem. Commun. 2011, 47, 10827–10829.
3
842
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