Br?nsted acid-catalyzed radical C[sbnd]H functionalization of acetone with N-allyl anilines to give 3-(3-oxobutyl)indolines

Article abstract of DOI:10.1016/j.tetlet.2019.04.017

K₂S₂O₈ was unprecedentedly used instead of tert-butyl hydroperoxide (TBHP) in Br?nsted acid-assisted catalytic strategy for ketonic radical generation, and the first Br?nsted acid-catalyzed radical C[sbnd]H functionalizati

Full text of DOI:10.1016/j.tetlet.2019.04.017

Tetrahedron Letters xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Brønsted acid-catalyzed radical CAH functionalization of acetone with
N-allyl anilines to give 3-(3-oxobutyl)indolines
a
Xiufang Wang a, Xiaohui Zhao a, Xiulan Li a, Bojie Huo a, Ying Dong b, Deqiang Liang a, , Yinhai Ma
⇑
a Yunnan Engineering Technology Research Center for Plastic Films, Department of Chemistry, Kunming University, Kunming 650214, China
b College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal University, Jinan 250014, China
a r t i c l e i n f o
a b s t r a c t
Article history:
K2S2O8 was unprecedentedly used instead of tert-butyl hydroperoxide (TBHP) in Brønsted acid-assisted
catalytic strategy for ketonic radical generation, and the first Brønsted acid-catalyzed radical CAH func-
tionalization of acetone across unactivated alkenes is presented. In the presence of TsOH and K2S2O8,
N-allyl anilines underwent addition/cyclization cascade with acetone to afford 3-(3-oxobutyl)indolines
with exo-selectivity and broad substrate scope at a relatively low temperature.
Received 25 February 2019
Revised 27 March 2019
Accepted 8 April 2019
Available online xxxx
Ó 2019 Elsevier Ltd. All rights reserved.
Keywords:
CAH functionalization
Radical cyclization
Indolines
Unactivated alkenes
Introduction
radicals provides an exciting opportunity for umpolung CAH func-
tionalization of ketones with nucleophiles (Scheme 1a2) [9–12]. A
Ketones are a class of privileged compounds in textbooks, for
the carbonyl group is one of the most powerful and versatile func-
tionalities [1]. CAH functionalization is considered an ideal process
due to its atom- and step-economy as well as the abundance of
CAH bonds [2]. Because of the significant acidity of ketonic
cyclization process might facilitate some polarity-mismatched
conjugate addition of ketonic radicals to electron-deficient olefins
[13–16], and the rules of polarity-matching [20,21] might be inap-
plicable to radical/radical cross-coupling [17,18]. Ketonic radicals
are usually produced at a high temperature under the catalysis of
a transition metal, and metal-free protocols have also been devel-
oped. In 2014, Klussmann and co-workers reported a Brønsted
acid-assisted catalytic strategy for ketonic radical generation
(Scheme 1b) [12], by which ketonic radicals could be produced at
a substantially reduced temperature. Such strategy is promising
and has been applied to the difunctionalization of styrenes [12],
the development of low-temperature radical initiators [22], the
cross-coupling of aldehydes [18], and the synthesis of oxindoles
[14] and isoquinolinonediones [16]. However, in all these reac-
tions, the use of tert-butyl hydroperoxide (TBHP) is essential, and
this nucleophilic peroxide adds to ketones to afford highly unstable
alkenyl peroxides which decompose into ketonic radicals. During
our ongoing research on radical chemistry [23], it was found that
K2S2O8 and Oxone are superior peroxides for Brønsted acid-cat-
alyzed CAH functionalization of acetone across unactivated
alkenes. Intrigued by related new chemistry and given that the
two salts are much safer and cheaper than TBHP, we conducted a
research on this reaction (Scheme 1c), wherein inexpensive ace-
tone was used as the radical precursor, unactivated alkenic bonds
acted as radical acceptors, and 2-unsubstituted indolines bearing
aACAH bonds, ketones as carbon nucleophiles are involved in a
wide range of well-known transformations such as aldol condensa-
tion [3], Mannich reaction [4], and Michael addition [5], in the
presence of a base, acid or organocatalyst (Scheme 1a1). In some
palladium-catalyzed C(sp3)-H functionalizations, the nucleophilic-
ity of ketones is enhanced by metal complexation [6,7], and in sev-
eral radical reactions, simple ketones were reported to serve as
nucleophilic radical acceptors [8]. However, while acidic
aACAH
bonds render ketones highly active nucleophiles, ketones are inert
radical precursors, because polar bonds are prone to heterolysis
and difficult to cleave homolytically. Hence, CAH functionalization
reactions of simple ketones involving ketonic radicals are rather
limited [9–18].
Over the past decade, radical reaction has been experiencing a
rapid development, and it offers unique reaction pathways which
often give products that are inaccessible by ionic mechanisms
[19]. For example, the formation of electrophilic ketone-derived
⇑
Corresponding author.
E-mail address: liangdq695@nenu.edu.cn (D. Liang).
https://doi.org/10.1016/j.tetlet.2019.04.017
0040-4039/Ó 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: X. Wang, X. Zhao, X. Li et al., Brønsted acid-catalyzed radical CAH functionalization of acetone with N-allyl anilines to give 3-(3-
oxobutyl)indolines, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.04.017

2
X. Wang et al. / Tetrahedron Letters xxx (xxxx) xxx
The indoline is a common structural motif that is found in
numerous alkaloids and synthetic bioactive molecules [24]. In
indole chemistry, however, indoline synthesis is more difficult
than the assembly of other indolic variants such as oxindoles
[25]. The access to indolines is mainly restricted to the dearomati-
zation reaction of indoles, which leads to 2-substituted indolines
[26]. Although 2-unsubstituted indolines could be prepared
through the reduction of parent oxindoles (Scheme 1d), such syn-
thesis suffers from severe functional-group intolerance due to
highly reductive conditions [27]. In 2018, Pan and Yu reported a
similar and elegant 3-(3-oxobutyl)indoline synthesis under
metal-free conditions, yet their protocol is associated with a higher
reaction temperature, a higher-price peroxide, and the intolerance
of sulfonyl N-protecting groups (PGs) [10].
Results and discussion
We began our studies by investigating the acid-catalyzed addi-
tion of acetone radical to N-(2-methylallyl) acetanilide 1a (Table 1).
Upon exposure of 1a to 10 mol% TsOH and 2 equiv of TBHP in ace-
tone at 80 °C, the addition/cyclization cascade occurred to afford 3-
(3-oxobutyl)indoline 2a in moderate yields (entries 1 and 2). No
reaction occurred in the absence of TsOH (entry 3), or under the
catalysis of a transition-metal salt such as CuI, FeCl3 or CoCl2 (entry
4). With TsOH as the catalyst, non-nucleophilic peroxides such as
di-tert-butyl peroxide (DTBP), dicumyl peroxide (DCP), benzoyl
peroxide (BPO) and tert-butyl peroxybenzoate (TBPB), proved inef-
fective (entry 5). Interestingly, the use of non-nucleophilic K2S2O8
(entry 6) or nucleophilic Oxone (entry 7) both furnished 3-(3-oxo-
butyl)indoline 2a in good yields. Both salts are very cheap and
quite safe, and K2S2O8 was chosen for further studies because of
Scheme 1. Brønsted acid-assisted radical strategy for CAH functionalization of
ketones.
ketone side chains at the 3-position were provided. This protocol
features exo selectivity, broad substrate scope, and relatively low
reaction temperature.
Table 1
Optimization.a
entry
catalyst (mol%)
oxidant (equiv)
T (°C)
Yield (%)
1
2
3
4
5
6
7
8
TsOH (10)
TsOH (10)
none
CuI, FeCl3 or CoCl2 (10)
TsOH (10)
TsOH (10)
TsOH (10)
TfOH (10)
MsOH (10)
H2SO4 (10)
TFA (10)
TBAI (10)
CuI (10)
FeCl2 (10)
CoCl2 (10)
MnCl2 (10)
Cu(NO3)2, FeCl3, AgNO3 or NiCl2 (10)
TsOH (10)
TBHPb (2)
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
50
80
80
80
58
53
nr
TBHPc (2)
TBHPb (2)
TBHPb (2)
nr
DTBP, DCP, BPO or TBPB (2)
K2S2O8 (2)
Oxone (2)
trace
76
73
71
66
74
62
34
28
36
35
38
nr
32
nr
nr
68
75
69
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (2)
K2S2O8 (1.5)
K2S2O8 (1.2)
9
10
11
12
13
14
15
16
17
18d
19e
20
21
22
23
TsOH (10)
TsOH (10)
TsOH (5)
TsOH (10)
TsOH (10)
a
b
c
Reaction conditions: 1a (0.2 mmol), solvent (1.2 mL), Ar, 24 h.
5.0–6.0 mol/L in decane.
70% aqueous.
The reaction was run in CH3CN using 20 equiv of acetone.
The reaction was run in DCE, chlorobenzene, EtOAc, THF, CH3NO2, DMSO, or EtOH using 20 equiv of acetone.
d
e
Please cite this article as: X. Wang, X. Zhao, X. Li et al., Brønsted acid-catalyzed radical CAH functionalization of acetone with N-allyl anilines to give 3-(3-
oxobutyl)indolines, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.04.017

X. Wang et al. / Tetrahedron Letters xxx (xxxx) xxx
3
Table 2
its impressively low price. An examination of other Brønsted acids
Scope.a
demonstrated that TfOH (entry 8), MsOH (entry 9), H2SO4 (entry
10), and even trifluoroacetic acid (TFA, entry 11) are all usable cat-
alysts, providing indoline 2a in slightly decreased yields. Whereas
only poor yields of 2a were achieved using tetrabutylammonium
iodide (TBAI, entry 12), CuI (entry 13), FeCl2 (entry 14), CoCl2
(entry 15), or MnCl2 (entry 16) as the catalyst, no reaction occurred
under the catalysis of Cu(NO3)2, FeCl3, AgNO3 or NiCl2 (entry 17).
When the reaction was performed in CH3CN using 20 equiv of ace-
tone as the radical precursor, indoline 2a was delivered in a poor
yield. No reaction occurred in other solvents, including 1,2-dichlor-
oethane (DCE), chlorobenzene, EtOAc, tetrahydrofuran (THF), CH3-
NO2, dimethylsulfoxide (DMSO), and EtOH (entry 19). While this
addition/cyclization cascade did not proceed at 50 °C (entry 20),
a good yield of 2a could still be obtained using 1.5 equiv of
K2S2O8 (entry 22). With a reduced loading of the catalyst (entry
21) or using 1.2 equiv of K2S2O8 (entry 23), product 2a was fur-
nished in slightly diminished yields.
A variety of 3-(3-oxobutyl)indolines 2 could be prepared from
their parent N-allylated anilines 1 (Table 2). Allylated anilines
bearing a methyl, bromo, chloro, or phenyl group at the para posi-
tion of the N-aryl group reacted with acetone to give 5-substituted
indolines 2b-e in moderate to high yields. The propionyl-protected
aniline is also a competent substrate, delivering indoline product
2f in 70% yield, while indolines 2g,h bearing a bulkier octanoyl
or pivaloyl N-PG were provided in relatively modest yields, proba-
bly as a result of steric hindrance. The N-allylated aniline protected
by 3-chlorobenzoyl group is less reactive, and its reaction was per-
formed at 120 °C. Interestingly, desired indoline product 2i was
produced in only 25% yield, along with 7-chloro 3,4-dihydroiso-
quinolin-1-one product 2i’ in 33% yield. When allylated N-benzyl
or -methyl benzamides were used as substrates at 120 °C, cycliza-
tive arylation process occurred on the benzoyl ring and also at the
less hindered position, furnishing 3,4-dihydroisoquinolin-1-one
products 2j1,2 albeit in poor yields. Sulfonyl N-PGs were also toler-
ated, and N-allylated anilines protected by an ethanesulfonyl,
methanesulfonyl, dimethylsulfamoyl, benzenesulfonyl, 4-methyl-
benzenesulfonyl, 2-methylbenzenesulfonyl, 4-bromobenzenesul-
fonyl group reacted to yield sulfonyl indolines 2k-m in moderate
to high yields. The N-allylated aniline having a 2-chloro group
proved to be a challenging substrate, giving 7-chloro indoline 2n
in only 18% yield, probably due to steric conflict. A substituent at
the meta position of the N-aryl group is also compatible with this
transformation, and 4-chloro indoline 2o was prepared from the
parent acetanilide in a moderate yield, along with trace amounts
of unidentified products that defy isolation. In the case of 3-
chloroaniline having a N-octanoyl group, 4-chloro indoline 2p
was delivered in a moderate yield as well, whereas regioisomeric
6-substituted counterpart 2p’ was isolated in 7% yield. Interest-
ingly, indoline products 2o,p which were produced through the
ring closure occurred at the more hindered position were major
isomers, and the origin might be associated with intermediate
stability.
aReaction conditions: 1 (0.2 mmol), TsOH (0.02 mmol), K2S2O8 (0.3 mmol), acetone
(1.2 mL), Ar, 80 °C, 24 h.
bThe reaction was run at 120 °C.
cCyclopentanone or cyclohexanone was used as the solvent.
dThe reaction was run at 160 °C, and 3-methylbutan-2-one was used as the solvent
instead of acetone.
carbonyl carbon is more electrophilic and less hindered. In the
cases of cyclohexanone or cyclopentanone, unidentified products
were produced, yet NMR analyses suggest that they were probably
not derived from N-allyl anilines. Nonetheless, 3-methylbutan-2-
one reacted at a tremendously elevated temperature of 160 °C
under otherwise standard conditions to afford kinetically con-
trolled indoline product 2r in 37% yield, along with the substrate
recovered in 41% yield.
To probe the mechanism of this transformation, radical trap-
ping experiments were carried out with 2,2,6,6-tetram-
ethylpiperidine-1-oxyl (TEMPO) or butylated hydroxytoluene
(BHT) as the radical scavenger (Scheme 2a). In the presence of
1.2 equiv of either TEMPO or BHT, the addition/cyclization cas-
cades of model substrate 1a under otherwise standard conditions
did not proceed. Furthermore, in BHT experiments acetone-BHT
adduct 3 and hydroxyl-BHT adduct 4 were isolated in 12% and
According to Baldwin’s rule, 6-endo-trig mode of ring closure
might be a competing process with the present reaction [28]. After
we achieved excellent exo selectivity in all the above reactions, we
further examined as substrates simple N-allyl anilines without the
methyl branch. To our delight, 5-exo-trig products 2q were still
exclusively afforded, and no endo product was observed. Unfortu-
nately, the attempt to extend the reaction to other simple carbonyl
compounds with N-(4-chlorophenyl)-N-(2-methylallyl)ethanesul-
fonamide as the substrate met with no success even at 120 °C,
and tested solvents include 3-methylbutan-2-one, pinacolone,
pentan-3-one, 2,4-dimethylpentan-3-one, acetophenone, cyclo-
hexanone, cyclopentanone, ethyl acetate, and N,N-dimethylac-
etamide. Only acetone is usable, and this might be because its
Please cite this article as: X. Wang, X. Zhao, X. Li et al., Brønsted acid-catalyzed radical CAH functionalization of acetone with N-allyl anilines to give 3-(3-
oxobutyl)indolines, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.04.017

4
X. Wang et al. / Tetrahedron Letters xxx (xxxx) xxx
used instead of TBHP, and this is the first Brønsted acid-catalyzed
radical CAH functionalization of acetone across unactivated
alkenes.
Acknowledgments
We gratefully acknowledge the financial support from the
National Natural Science Foundation of China (21702083), the
Program for Innovative Research Team (in Science and Technology)
in Universities of Yunnan Province, and the Yunnan Ten Thousand
Talent Program for Young Top-Notch Talents.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2019.04.017.
References
[1] (a) S. Liang, K. Xu, C. Zeng, H. Tian, B. Sun, Adv. Synth. Catal. 360 (2018) 4266–
4292;
(b) J.R. Hummel, J.A. Boerth, J.A. Ellman, Chem. Rev. 117 (2017) 9163–9227;
(c) R. Cano, A. Zakarian, G.P. McGlacken, Angew. Chem. Int. Ed. 56 (2017)
9278–9290, For recent reviews, see:.
[2] (a) S. Tang, L. Zeng, A. Lei, J. Am. Chem. Soc. 140 (2018) 13128–13135;
(b) S. Tang, Y. Liu, A. Lei, Chem 4 (2018) 27–45;
Scheme 2. Mechanism.
(c) L. Revathi, L. Ravindar, W. Fang, K.P. Rakesh, H. Qin, Adv. Synth. Catal. 360
(2018) 4652–4698, For recent reviews, see:.
[3] (a) Y. Yamashita, T. Yasukawa, W. Yoo, T. Kitanosono, S. Kobayashi, Chem. Soc.
Rev. 47 (2018) 4388–4480;
(b) W. Gati, H. Yamamoto, Acc. Chem. Res. 49 (2016) 1757–1768.
[4] M. Arend, B. Westermann, N. Risch, Angew. Chem. Int. Ed. 37 (1998) 1044–
1070.
[5] B.E. Rossiter, N.M. Swingle, Chem. Rev. 92 (1992) 771–806.
[6] (a) W.C. Fu, B. Zheng, Q. Zhao, W.T.K. Chan, F.Y. Kwong, Org. Lett. 19 (2017)
4335–4338;
7% yields, respectively, suggesting that acetone radical and hydro-
xyl radical might be involved in this reaction.
Interestingly, when the model reaction under otherwise stan-
dard conditions was quenched after 2 h, only trace amounts of
indoline product 2a were detected, whereas 48% yield of 2a was
obtained after 6 h (Scheme 2b). These control experiments suggest
that the title reaction has an induction period.
(b) Y. Wu, W.C. Fu, C. Chiang, P.Y. Choy, F.Y. Kwong, A. Lei, Chem. Commun. 53
(2017) 952–955;
A tentative mechanism is proposed (Scheme 2c). According to
persulfate chemistry [29,30], K2S2O8 could react with minute
quantities of water in acetone to give a hydroxyl radical and a sul-
fate radical anion as well as a bisulfate anion, and the cross-cou-
pling of the two radicals could occur to afford the
peroxymonosulfate anion A. In light of Klussmann’s pioneering
works, a nucleophilic peroxide is essential for the Brønsted acid-
assisted ketonic radical generation [12,22], yet non-nucleophilic
K2S2O8 and nucleophilic Oxone, KHSO5 in the form of triple salt
2KHSO5 KHSO4 K2SO4, are both usable peroxides for the title reac-
tion (entries 6 and 7, Table 1). Thus, the induction period (Sche-
me 2b) might reflect the fact that K2S2O8 is only a pre-initiator
which needs to undergo the above transformations to form the
active initiator of peroxymonosulfate anion A. Then A adds to
acid-activated acetone to afford peroxyketal B, which eliminates
a molecule of water to give alkenyl peroxide C. C is highly unstable,
and the homolysis of its peroxy bond leads to resonance-stabilized
acetone radical and a sulfate radical anion. The acetone radical
adds to the unactivated olefinic bond of substrate 1a to give alkyl
radical D, which cyclizes to ring closure intermediate E through
intramolecular radical tapping by the phenyl group. Hydrogen-
atom transfer from E to a sulfate anionic radical ensues, affording
the final product 3-(3-oxobutyl)indoline 2a as well as a bisulfate
anion.
(c) C. Lei, J. Cao, J. Zhou, Org. Lett. 18 (2016) 6120–6123;
(d) C. Yang, K. Zhang, Z. Wu, H. Yao, A. Lin, Org. Lett. 18 (2016) 5332–5335;
(e) P.M. MacQueen, A.J. Chisholm, B.K.V. Hargreaves, M. Stradiotto, Chem. Eur.
J. 21 (2015) 11006–11009;
(f) X. Huo, M. Quan, G. Yang, X. Zhao, D. Liu, Y. Liu, W. Zhang, Org. Lett. 16
(2014) 1570–1573, For recent examples of palladium-catalyzed C-H
functionalization of acetone, see:.
[7] A rhodium-catalyzed C-H functionalization of acetone was also reported by
Dong and co-workers: F. Mo, G. Dong, Science 345 (2014) 68À72.
[8] (a) Acetone serving as a nucleophilic radical acceptor: Y. Lv, W. Pu, J. Niu, Q.
Wang, Q. Chen Tetrahedron Lett. 59 (2018) 1497–1500;
(b) L. Li, W. Huang, L. Chen, J. Dong, X. Ma, Y. Peng, Angew. Chem. Int. Ed. 56
(2017) 10539–10544;
(c) Z. Yang, J. Li, J. Hua, T. Yang, J. Yi, C. Zhou, Synlett 28 (2017) 2325–2329;
(d) Y. Lv, Y. Li, T. Xiong, Y. Lu, Q. Liu, Q. Zhang, Chem. Commun. 50 (2014)
2367–2369.
[9] (a) Y. Fan, S. Li, J. Bao, L. Shi, Y. Yang, F. Yu, P. Gao, H. Wang, L. Zhong, Y. Sun,
Green Chem. 20 (2018) 3450–3456;
(b) Y. Tian, C. Sun, R.X. Tan, Z. Liu, Green Chem. 20 (2018) 588–592;
(c) Q. Wang, Z. Chen, C. Zhou, B. Xiong, P. Zhang, C. Yang, Y. Liu, Q. Zhou,
Tetrahedron Lett. 59 (2018) 4551–4556;
(d) X. Chu, H. Meng, Y. Zi, X. Xu, S. Ji, X. Chu, H. Meng, Y. Zi, X. Xu, S. Ji, Chem.
Eur. J. 20 (2014) 17198–17206.
[10] C. Pan, Z. Yang, D. Gao, J. Yu, Org. Biomol. Chem. 16 (2018) 6035–6038.
[11] (a) R. Zhang, S. Jin, Q. Liu, S. Lin, Z. Yan, J. Org. Chem. 83 (2018) 13030–13035;
(b) C. Xu, Y. Han, S. Chen, D. Xu, B. Zhang, Z. Shan, S. Du, L. Xu, P. Gong,
Tetrahedron Lett. 59 (2018) 260–263;
(c) Y. Wu, B. Huang, Y. Zhang, X. Wang, J. Dai, J. Xu, H. Xu, Org. Biomol. Chem.
14 (2016) 5936–5939;
(d) X. Lan, N. Wang, W. Zhang, J. Wen, C. Bai, Y. Xing, Y. Li, Org. Lett. 17 (2015)
4460–4463;
(e) G. Yan, A.J. Borah, L. Wang, Z. Pan, S. Chen, X. Shen, X. Wu, Tetrahedron
Lett. 56 (2015) 4305–4307.
[12] B. Schweitzer-Chaput, J. Demaerel, H. Engler, M. Klussmann, Angew. Chem. Int.
Ed. 53 (2014) 8737–8740.
Conclusions
[13] (a) Y. Zhao, N. Sharma, U.K. Sharma, Z. Li, G. Song, E.V. Van der Eycken, Chem.
Eur. J. 22 (2016) 5878–5882;
(b) J. Zhang, Y. Liu, R. Song, G. Jiang, J. Li, Synlett 25 (2014) 1031–1035;
(c) H. Wang, L. Guo, X. Duan, Chem. Commun. 49 (2013) 10370–10372.
[14] (a) X. Xia, S. Zhu, M. Zeng, Z. Gu, H. Wang, W. Li, Tetrahedron 71 (2015) 6099–
6103;
In summary, a Brønsted acid-catalyzed radical addition/cycliza-
tion cascade of N-allyl anilines with acetone is developed, affording
3-(3-oxobutyl)indolines with exo-selectivity and broad substrate
scope at a relatively low temperature. K2S2O8 was unprecedentedly
Please cite this article as: X. Wang, X. Zhao, X. Li et al., Brønsted acid-catalyzed radical CAH functionalization of acetone with N-allyl anilines to give 3-(3-
oxobutyl)indolines, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.04.017

X. Wang et al. / Tetrahedron Letters xxx (xxxx) xxx
5
(b) E. Boess, S. Karanestora, A. Bosnidou, B. Schweitzer-Chaput, M. Hasenbeck,
[24] (a) S. Dadashpour, S. Emami, Eur. J. Med. Chem. 150 (2018) 9–29;
(b) N. Chadha, O. Silakari, Eur. J. Med. Chem. 134 (2017) 159–184;
M. Klussmann, Synlett 26 (2015) 1973–1976.
[15] Y. Yu, S. Zhuang, P. Liu, P. Sun, J. Org. Chem. 81 (2016) 11489–11495.
[16] S. Zhu, P. Zhou, X. Xia, RSC Adv. 6 (2016) 63325–63330.
[17] K. Rybicka-Jasin´ ska, K. Orłowska, M. Karczewski, K. Zawada, D. Gryko, Eur. J.
Org. Chem. (2018) 6634–6642.
(c) S. Sugimoto, M. Naganuma, T. Kanai, J. Gastroenterol. 51 (2016) 853–861;
(d) T.V. Sravanthi, S.L. Manju, Eur. J. Pharm. Sci. 91 (2016) 1–10.
[25] (a) K. Nagarajua, D. Ma, Chem. Soc. Rev. 47 (2018) 8018–8029;
(b) Z. Xu, Q. Wang, J. Zhu, Chem. Soc. Rev. 47 (2018) 7882–7898;
(c) Y. Wang, F. Xie, B. Lin, M. Cheng, Y. Liu, Chem. Eur. J. 24 (2018) 14302–
14315.
[18] X. Shen, A.J. Borah, X. Cao, W. Pan, G. Yan, X. Wu, Tetrahedron Lett. 56 (2015)
6484–6487.
[19] A. Studer, D.P. Curran, Angew. Chem. Int. Ed. 55 (2016) 58–102.
[20] B.P. Roberts, Chem. Soc. Rev. 28 (1999) 25–35, For a review, see:.
[21] (a) For selected examples: A. Hu, J. Guo, H. Pan, Z. Zuo Science 361 (2018)
668–672;
[26] (a) C. Zheng, S. You, Chem 1 (2016) 830–857;
(b) C. Zhuo, C. Zheng, S. You, Acc. Chem. Res. 47 (2014) 2558–2573;
(c) S.P. Roche, J.A. Porco Jr., Angew. Chem. Int. Ed. 50 (2011) 4068–4093.
[27] (a) L. Wang, S. Li, M. Blümel, R. Puttreddy, A. Peuronen, K. Rissanen, D. Enders,
Angew. Chem. Int. Ed. 56 (2017) 8516–8521;
(b) A. Trowbridge, D. Reich, M.J. Gaunt, Nature 561 (2018) 522–527;
(c) X. Guo, O.S. Wenger, Angew. Chem. Int. Ed. 57 (2018) 2469–2473;
(d) C. Le, Y. Liang, R.W. Evans, X. Li, D.W.C. MacMillan, Nature 547 (2017) 79–
83.
(b) D. Katayev, H. Kajita, A. Togni, Chem. Eur. J. 23 (2017) 8353–8357;
(c) A.S. Filatov, N.A. Knyazev, A.P. Molchanov, T.L. Panikorovsky, R.R. Kostikov,
A.G. Larina, V.M. Boitsov, A.V. Stepakov, J. Org. Chem. 82 (2017) 959–975, For
recent examples, see:.
[22] B. Schweitzer-Chaput, E. Boess, M. Klussmann, Org. Lett. 18 (2016) 4944–4947.
[23] (a) Y. Li, R. Yang, X. Zhao, Y. Yao, S. Yang, Q. Wu, D. Liang, Synth. Commun. 46
(2019) 735–743;
[28] (a) J.K. Baldwin, J. Chem. Soc. Chem. Commun. (1976) 734–736;
(b) J.K. Baldwin, R.C. Thomas, L.I. Kruse, L. Silberman, J. Org. Chem. 42 (1977)
3846–3852.
[29] For a review: L.W. Matzek, K.E. Carter Chemosphere 151 (2016) 178–188.
[30] (a) M. Xu, X. Gu, S. Lu, Z. Qiu, Q. Sui, Z. Miao, X. Zang, X. Wu, J. Hazard. Mater.
286 (2015) 7–14;
(b) Y. Li, Y. Chang, Y. Li, C. Cao, J. Yang, B. Wang, D. Liang, Adv. Synth. Catal. 360
(2018) 2488–2492;
(c) D. Liang, Q. Dong, P. Xu, Y. Dong, W. Li, Y. Ma, J. Org. Chem. 83 (2018)
(1986) 11978–11981;
(d) D. Liang, D. Ge, Y. Lv, W. Huang, B. Wang, W. Li, J. Org. Chem. 83 (2018)
4681–4691;
(b) R.L. Johnson, P.G. Tratnyek, R.O. Johnson, Environ. Sci. Technol. 42 (2008)
9350–9356;
(e) D. Liang, Y. Li, S. Gao, R. Li, X. Li, B. Wang, H. Yang, Green Chem. 19 (2017)
3344–3349;
(c) R.H. Waldemer, P.G. Tratnyek, R.L. Johnson, J.T. Nurmi, Environ. Sci.
Technol. 41 (2007) 1010–1015;
(f) D. Liang, X. Li, Q. Lan, W. Huang, L. Yuan, Y. Ma, Tetrahedron Lett. 57 (2016)
2207–2210.
(d) I.M. Kolthoff, I.K. Miller, J. Am. Chem. Soc. 73 (1951) 3055–3059, For
selected examples, see:.
Please cite this article as: X. Wang, X. Zhao, X. Li et al., Brønsted acid-catalyzed radical CAH functionalization of acetone with N-allyl anilines to give 3-(3-
oxobutyl)indolines, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.04.017