Palladium-catalyzed difunctionalization/dearomatization ofN-benzylacrylamides with α-carbonyl alkyl bromides: facile access to azaspirocyclohexadienones

Article abstract of DOI:10.1039/d1ob01405f

An efficient palladium-catalyzed difunctionalization/dearomatization ofN-benzylacrylamides with α-carbonyl alkyl bromides as alkyl radical precursors has been described. Various α-carbonyl alkyl bromides, including α-bromoalkyl esters and ketones, reacted

Full text of DOI:10.1039/d1ob01405f

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Palladium-catalyzed difunctionalization/
dearomatization of N-benzylacrylamides with
α-carbonyl alkyl bromides: facile access to
azaspirocyclohexadienones†
Cite this: DOI: 10.1039/d1ob01405f
Received 20th July 2021,
Accepted 19th August 2021
DOI: 10.1039/d1ob01405f
Chuan-Chong Peng,a Li-Jun Wu *a and Shao-Feng Pi*b
rsc.li/obc
An efficient palladium-catalyzed difunctionalization/dearomatiza- mediated difunctionalization of alkenes with alkyl bromides,
tion of N-benzylacrylamides with α-carbonyl alkyl bromides as which allowed the construction of a C(sp3)–C(sp3) bond and a
alkyl radical precursors has been described. Various α-carbonyl C(sp3)–C(sp2) bond via an alkyl radical addition and cycliza-
alkyl bromides, including α-bromoalkyl esters and ketones, tion process. Then, the Wu group4b disclosed a palladium-cata-
reacted smoothly to provide important azaspirocyclohexadienones lyzed intermolecular cyclization of unactivated alkyl halides
in moderate to excellent yields. In addition, mechanistic studies with alkenes for the preparation of structurally complex hetero-
suggested that the reaction proceeded via a radical pathway.
polycycles. Although these methods were extended to intro-
duce alkyl radicals into CvC bonds, the substrate scope of
alkenes is narrow and only a few examples have been reported.
Therefore, practical and straightforward strategies for palla-
dium-catalyzed difunctionalization of alkyl halides as alkyl
radical precursors with alkenes are highly desirable.
Introduction
Functionalizations of alkenes have been widely exploited as an
efficient and straightforward tool to prepare highly functiona-
lized skeletons in organic synthesis.1 Among them, transition-
metal-catalyzed difunctionalization of alkenes with alkyl
halides is undoubtedly an attractive strategy because it can
directly construct important carbo- and hetero-cyclic
compounds.2–4 Despite the significant progress in this
research field, palladium-catalyzed difunctionalization reac-
tions of alkyl halides as alkyl radical precursors with alkenes
to construct valuable skeleton molecules still remain a promi-
nent challenge. Such transformations are difficult because
intermediates A, which are generated through alkylation of
alkyl halides with alkenes, tend to undergo the Heck-type
coupling reaction via a β-hydride elimination process,5 gener-
ating conjugated alkenes (Scheme 1a). Recently, some effective
strategies4 wherein alkyl halides are converted into alkyl rad-
icals to initiate the intramolecular cyclization with alkenes
have been developed by using palladium in catalytic systems
(Scheme 1b). In 2016, Li and co-workers4a reported the Pd-
On the other hand, azaspirocyclohexadienones are impor-
tant structural motifs that are widely present in numerous
natural products, biologically active molecules and key inter-
mediates in organic synthesis.6 Therefore, considerable efforts
have been devoted to the development of efficient and versatile
strategies for the synthesis of azaspirocyclohexadienones.7–10
Recently, dearomatization of N-benzylacrylamides with rad-
icals (e.g. HCF2, CF3 and CF3SO2) for the construction of azas-
pirocyclohexadienones was established via a radical addition,
intramolecular cyclization and dearomatization process.10
aInstitute of Applied Chemistry, Central South University of Forestry and Technology,
Changsha, 410004, China. E-mail: t20202522@csuft.edu.cn
bSchool of Materials and Chemical Engineering, Hunan Provincial Key Laboratory of
Environmental Catalysis & Waste Recycling, Hunan Institute of Engineering,
Xiangtan, 411104, China. E-mail: psfhunan@126.com
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
d1ob01405f
Scheme 1 Palladium-catalyzed functionalization of alkenes with alkyl
halides.
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Based on previous reports,4,10 we deduced that the alkyl rad- and Pd(PPh3)4, were less efficient than Pd(OAc)2 (entry 1 and
icals from alkyl halides might undergo addition across the entries 3–6). Although the reaction could occur in the absence
CvC bonds in N-benzylacrylamides followed by an intra- of HP(Ph)2, a lower yield was obtained (entry 7). This result
molecular cyclization and dearomatization process by using a suggested that the phosphorus ligand was not essential for the
palladium catalytic system. Therefore, we report a novel palla- reaction, but only promoted this transformation. When PPh3,
dium-catalysed
difunctionalization/dearomatization
of Dppe, P(p-tol)3 or PCy3 was used instead of HP(Ph)2 as the
N-benzylacrylamides with α-carbonyl alkyl bromides. The strat- ligand, it led to diminished yields (entries 8–11). Surprisingly,
egy enables the construction of three chemical bonds, includ- other silver salts and a base, including AgNO3, Ag2O and
ing two C–C bonds and a CvO bond, in a single reaction and Na2CO3, showed no catalytic activities in this reaction (entries
represents a novel method for the introduction of alkyl rad- 12–14). These results indicated that Ag2CO3 acted as both a
icals into the CvC bonds to assemble azaspirocyclohexadie- base and an oxidant promoter. Increasing or decreasing
nones through a radical-mediated pathway.
the amount of Ag2CO3 reduced the yield of 3aa slightly (entries
We began our investigation by focusing on the palladium- 15 and 16). Subsequently, the amount of added H2O was
catalyzed difunctionalization/dearomatization between N-(4- evaluated, and the best addition turned out to be 2.0 equiv.,
(benzyloxy)benzyl)-N-(tert-butyl)methacrylamide
(1a)
and and without H2O, the transformation afforded 3aa with a
methyl 2-bromopropanoate (2a) (Table 1). Gratifyingly, the lower yield (entries 17–19). Further solvent screening showed
treatment of N-benzylacrylamide (1a) with α-carbonyl alkyl that DCE was superior to toluene, CH3CN and DMF
bromide (2a), 5 mol% of Pd(OAc)2, 10 mol% HP(Ph)2, 2 equiv. (entries 20–22). Finally, the reaction temperature was also
of Ag2CO3 and 2 equiv. of H2O in DCE at 100 °C for 12 h tested, and the results revealed that the reaction at 100 °C was
afforded the desired product 3aa in 72% yield (entry 1). Both the best choice (entry 1 and entries 23 and 24). Pleasingly,
Pd(OAc)2 and Ag2CO3 played a crucial role in the reaction, as 1 mmol of N-benzylacrylamide (1a) was effectively converted
omission of any one resulted in no formation of 3aa (entry 2). into 3aa in an excellent yield under the optimal conditions
Other Pd catalysts, such as PdCl2, Pd(CH3CN)2Cl2, Pd2(dba)3 (entry 25).
With the optimized conditions in hand, we then set out to
investigate the reactivity of N-benzylacrylamides (1b–1i) with
various substituents (R) at the para-position of the benzene
Table 1 Screening of the optimal reaction conditionsa
ring (Table 2). Expectedly, a series of substrates with oxygen-
containing substituents (1b–1g), including OH, OMe, OTBS,
OTrt, OAc and OPiv, were well tolerated and afforded the
corresponding azaspirocyclohexadienone 3aa in moderate
yields. In particular, substrate 1d was a good candidate for the
transformation, affording the product in 81% yield. These
results suggested that substrate 1d has higher reactivity than
the other substrates (1b, 1c, 1e–1g) under the standard con-
ditions. However, when substituents such as H and F were at
the para-position of the benzene ring (1h and 1i), the reaction
was inactive and led to no generation of product 3aa. These
results showed that the oxygen of the cyclohexadienone moiety
Entry
Variation from the standard conditions
Yield (%)b
1
2
3
4
5
6
7
None
72
0
8
Without Pd(OAc)2 or Ag2CO3
PdCl2 instead of Pd(OAc)2
Pd(CH3CN)2Cl2 instead of Pd(OAc)2
Pd2(dba)3 instead of Pd(OAc)2
Pd(PPh3)4 instead of Pd(OAc)2
Without HP(Ph)2
51
30
21
22
53
46
61
5
8
9
PPh3 instead of HP(Ph)2
Dppe instead of HP(Ph)2
P(p-tol)3 instead of HP(Ph)2
PCy3 instead of HP(Ph)2
AgNO3 instead of Ag2CO3
Ag2O instead of Ag2CO3
Na2CO3 instead of Ag2CO3
Ag2CO3 (3 equiv.)
Ag2CO3 (1 equiv.)
Without H2O
H2O (1 equiv.)
H2O (3 equiv.)
Toluene instead of DCE
CH3CN instead of DCE
DMF instead of DCE
At 110 °C
At 90 °C
None
Table 2 Screening of the effect of N-benzylacrylamidesa
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25c
0
0
0
65
54
52
61
66
58
7
Trace
62
26
68
a Reaction conditions: 1a (0.2 mmol), 2a (1.5 equiv.), Pd(OAc)2
(5 mol%), HPPh2 (10 mol%), Ag2CO3 (2 equiv.), H2O (2 equiv.) and a Reaction conditions:
1
(0.2 mmol), 2a (1.5 equiv.), Pd(OAc)2
DCE (2 mL) at 100 °C (oil bath) under an argon atmosphere for 12 h. (5 mol%), HPPh2 (10 mol%), Ag2CO3 (2 equiv.), H2O (2 equiv.) and
b Isolated yield. c 1a (1 mmol) and DCE (4 mL) for 24 h.
DCE (2 mL) at 100 °C under an argon atmosphere for 12 h.
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should come from the oxygen-containing group in the that those with electron-donating CH3 and electron-withdraw-
transformation. ing Cl afforded the corresponding products 3og and 3pg in
In order to further explore the substrate scope of this trans- moderate yields. Unfortunately, substrate 1q bearing a methyl
formation, various α-carbonyl alkyl bromides and other substi- at the ortho-position of the benzene ring could not provide the
tuted N-benzylacrylamides were also investigated, and the desired product 3qg. These results showed that the steric influ-
results are presented in Table 3. Initially, a series of α-carbonyl ence of the substituents on the benzene ring plays an impor-
alkyl bromides (2b–2m), including α-bromoalkyl esters and tant role in the transformation. Interestingly, substrate 1r
ketones, were screened under the standard conditions. The smoothly underwent the reaction to afford product 3ra in 70%
results showed that secondary α-bromoalkyl esters (2b–2d) and yield.
a ketone (2e) could be smoothly converted into the corres-
To elucidate the mechanism of the reaction, several control
ponding products (3db–3de) in moderate yields. For example, experiments were performed (Scheme 2a and b). The palla-
substrates 2d and 2e were well tolerated in this transformation, dium-catalyzed difunctionalization/dearomatization of sub-
generating the desired products 3dd and 3de in 83% and 78% strate 1d with α-bromoalkyl ester 2a could not occur when a
yields, respectively. To our delight, the primary α-bromoalkyl radical inhibitor TEMPO was added and only product 4 was
ester 2f and ketones (2g–2l) were viable for the transformation obtained with 62% yield. Similar results were observed when
and reacted with N-benzylacrylamide 1d to afford the products BHT or hydroquinone was used instead of TEMPO. In the pres-
(3df–3dl) in 62%–76% yields, and the order of their reactivity ence of N-benzylacrylamide 1d, substrate 2a and 1,1-dipheny-
was as follows: electron-donating ketone > ester > electron- lalkene, compound 5aa was obtained as the major product.
withdrawing ketone. However, the tertiary α-bromoalkyl These results showed that the reaction proceeded via a radical
ester 2m was inert and led to no generation of product 3dm. pathway. To illustrate the synthetic utility of the transform-
Subsequently, various N-substituents (R4) of N-benzylacrylamides ation, product 3df was hydrolyzed to generate the azaspirocy-
were examined under the standard conditions. These sub- clohexadienone carboxylic acid 6aa in 85% yield (Scheme 2c).
strates with n-octyl, isopropyl, cyclopropyl, cyclopentyl and
On the basis of the experimental results and previous litera-
cyclohexyl substituents all provided the corresponding azaspir- ture studies,4,10–12 a plausible mechanism was proposed
ocyclohexadienones (3ja–3na) in good yields. When substrates (Scheme 3). Initially, alkyl radical B is generated by the reac-
with different substituents (R3) at the meta-position of the tion of α-carbonyl alkyl bromide 2a and the active [Pd0Ln]
benzene ring that reacted with 2g were screened, it was found species (generated in situ from Pd(OAc)2 and HPPh2) via a
single electron transfer (SET) process, and the active [Pd0Ln]
species is transformed into the [PdILn] species, followed by Ag
(I) oxidizing the [PdILn] species into the [PdIILn] species along
with the generation of Ag(0). Then, alkyl radical B upon
Table 3 The scope of N-benzylacrylamides (1) with α-carbonyl alkyl
bromides (2)a
addition across the CvC double bond in N-benzylacrylamide
1d affords the radical intermediate C, which followed by the
cyclization/dearomatization of intermediate C affords spirocyc-
lic intermediate D, which is oxidized by the active [PdIILn]
species to give the intermediate cation E. Finally, the inter-
mediate cation E reacts with the hydroxyl ion to form the
desired product 3aa. H2O probably stabilizes cation E and thus
promotes the transformation.
a Reaction conditions: 1 (0.2 mmol), 2 (1.5 equiv.), Pd(OAc)2 (5 mol%),
HPPh2 (10 mol%), Ag2CO3 (2 equiv.), H2O (2 equiv.) and DCE (2 mL) at
100 °C under an argon atmosphere for 12 h.
Scheme 2 Control experiments and application.
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3727; (h) E. Merino and C. Nevado, Chem. Soc. Rev., 2014,
43, 6598; (i) M. Wilken, S. Ortgies, A. Breder and I. Siewert,
ACS Catal., 2018, 8, 10901; ( j) A. D. Marchese, E. M. Larin,
B. Mirabi and M. Lautens, Acc. Chem. Res., 2020, 53, 1605.
2 (a) A. Fusano, S. Sumino, T. Fukuyama and I. Ryu, Org.
Lett., 2011, 8, 2114; (b) T. Soejima, K. Satoh and
M. Kamigaito, J. Am. Chem. Soc., 2016, 138, 944;
(c) M. Zhang, W. Li, Y. Duan, P. Xu, S. Zhang and C. Zhu,
Org. Lett., 2016, 18, 3266; (d) H. Yi, X. Zhang, C. Qin,
Z. Liao, J. Liu and A. Lei, Adv. Synth. Catal., 2014, 356,
2873; (e) Q. Wang, J. Huang and L. Zhou, Adv. Synth. Catal.,
2015, 357, 2479; (f) Y. Zou and J. Zhou, Chem. Commun.,
2014, 50, 3725; (g) G. Evano, N. Blanchard and M. Toumi,
Chem. Rev., 2008, 108, 3054; (h) S. Lou and G. C. Fu, J. Am.
Chem. Soc., 2010, 132, 5010; (i) X.-J. Wei, D.-T. Yang,
L. Wang, T. Song, L.-Z. Wu and Q. Liu, Org. Lett., 2013, 23,
6054; ( j) J.-H. Fan, J. Ynag, R.-J. Song and J.-H. Li, Org.
Lett., 2015, 17, 836; (k) R. S. Andrews, J. J. Becker and
M. R. Gagne, Angew. Chem., Int. Ed., 2010, 49, 7274;
(l) H. Kim and C. Lee, Angew. Chem., Int. Ed., 2012, 51,
12303.
3 (a) T. Nishikata, Y. Noda, R. Fujimoto and T. Sakashita,
J. Am. Chem. Soc., 2013, 135, 16372; (b) T. Xu and X. Hu,
Angew. Chem., 2015, 127, 1323; (c) S. Ishikawa, Y. Noda,
M. Wada and T. Nishikata, J. Org. Chem., 2015, 80, 7555;
(d) S. Tang, K. Liu, C. Liu and A. Lei, Chem. Soc. Rev., 2015,
44, 1070; (e) Y. Yamane, K. Miyazaki and T. Nishikata, ACS
Catal., 2016, 6, 7418; (f) M. Hu, R.-J. Song, X.-H. Ouyang,
F.-L. Tan, W.-T. Wei and J.-H. Li, Chem. Commun., 2016, 52,
3328; (g) J. Caruano, G. G. Muccioli and R. Robiette, Org.
Biomol. Chem., 2016, 14, 10134; (h) X.-H. Ouyang,
R.-J. Song, M. Hu, Y. Yang and J.-H. Li, Angew. Chem., Int.
Ed., 2016, 55, 3187; (i) G.-H. Pan, X.-H. Ouyang, M. Hu,
Y.-X. Xie and J.-H. Li, Adv. Synth. Catal., 2017, 359, 2564;
( j) S. N. Gockel, T. L. Buchanan and K. L. Hull, J. Am.
Chem. Soc., 2018, 140, 58; (k) T. L. Buchanan, S. N. Gockel,
A. M. Veatch, Y.-N. Wang and K. L. Hull, Org. Lett., 2021,
23, 4538.
Scheme 3 Proposed mechanism.
Conclusion
In summary, we have disclosed a convenient palladium-cata-
lyzed difunctionalization/dearomatization of N-benzylacrylamides
with α-carbonyl alkyl bromides for the preparation of azaspiro-
cyclohexadienones under mild conditions. The transformation
involves a radical pathway and proceeds via an alkyl radical
formation, radical addition, intramolecular cyclization and
dearomatization process. The reaction allows the one-step for-
mation of three chemical bonds, including two C–C bonds
and a CvO bond, which will be widely used to overcome
various challenges associated with the synthesis strategies of
azaspiro compounds. Studies on further exploration and
application of the difunctionalization/dearomatization of
N-benzylacrylamides with alkyl radicals are currently underway
in our laboratory.
Conflicts of interest
There are no conflicts to declare.
4 (a) J.-H. Fan, W.-T. Wei, M.-B. Zhou, R.-J. Song and J.-H. Li,
Angew. Chem., Int. Ed., 2014, 53, 6650; (b) X. Wu, G. Xiao,
Y. Ding, Y. Zhan, Y. Zhao, R. Chen and T.-P. Loh, ACS
Catal., 2020, 10, 14107.
Acknowledgements
We thank the Talent Introduction Fund of the Central South
University of Forestry and Technology (No. 2021YJ015) for
financial support.
5 (a) C. Liu, S. Tang, D. Liu, J. Yuan, L. Zheng, L. Meng and
A. Lei, Angew. Chem., Int. Ed., 2012, 51, 3638;
(b) J. W. Tucker, Y. Zhang, T. F. Jamison and
C. R. J. Stephenson, Angew. Chem., Int. Ed., 2012, 51, 4144;
(c) H. Jiang, C. Huang, J. Guo, C. Zeng, Y. Zhang and S. Yu,
Chem. – Eur. J., 2012, 18, 15158; (d) Q. Liu, H. Yi, J. Liu,
Y. Yang, X. Zhang, Z. Zeng and A. Lei, Chem. – Eur. J., 2013,
19, 5120; (e) C.-J. Walkentin, J. D. Nguyen, P. Finkbeiner
and C. R. J. Stephenson, J. Am. Chem. Soc., 2012, 134, 8875.
6 (a) W. M. Kazmierski, E. Furfine, A. Spaltenstein and
L. L. Wright, Bioorg. Med. Chem. Lett., 2002, 12, 3431;
(b) H. Shigehisa, J. Takayama and T. Honda, Tetrahedron
Lett., 2006, 47, 7301; (c) A. Ghoshal, A. Kumar,
D. Yugandhar, C. Sona, S. Kuriakose, K. Nagesh, M. Rashid
Notes and references
1 (a) I. I. Moiseev and M. N. Vargaftik, Coord. Chem. Rev.,
2004, 248, 2381; (b) M. Beller, J. Seayadd, A. Tillack and
H. Jiao, Angew. Chem., Int. Ed., 2004, 43, 3368;
(c) R. I. McDonald, G. Liu and S. S. Stahl, Chem. Rev., 2011,
111, 2981; (d) W. Wu and H. Jiang, Acc. Chem. Res., 2012,
45, 1736; (e) C. Zhang, C. Tang and N. Jiao, Chem. Soc. Rev.,
2012, 41, 3464; (f) S. E. Allen, R. R. Walvoord, R. P. Salinas
and M. C. Kozlowski, Chem. Rev., 2013, 113, 6234;
(g) Y. Shimizu and M. Kanai, Tetrahedron Lett., 2014, 55,
Org. Biomol. Chem.
This journal is © The Royal Society of Chemistry 2021

View Article Online
Organic & Biomolecular Chemistry
Communication
and S. K. Singh, Eur. J. Med. Chem., 2018, 152, 148;
(d) S. P. Roche and J. A. Proco Jr., Angew. Chem., Int. Ed.,
2011, 50, 4068; (e) Y.-L. Yang, F.-R. Chang and Y.-C. Wu, Helv.
Chim. Acta, 2004, 87, 1392; (f) G. A. Molander and M. Ronn,
J. Org. Chem., 1999, 64, 5183; (g) M.-P. Sauviat, J. Vercauteren,
N. Grimaud, M. Juge, M. Nebil, J.-Y. Petit and J.-F. Biard,
J. Nat. Prod., 2006, 69, 558; (h) T. Honda and H. Shigehisa,
J. F. Soule, Adv. Synth. Catal., 2019, 361, 445; (h) L.-J. Wu,
F.-L. Tan, M. Li, R.-J. Song and J.-H. Li, Org. Chem. Front.,
2017, 4, 350; (i) W. Wei, H. Cui, D. Yang, H. Yue, C. He,
Y. Zhang and H. Wang, Green Chem., 2017, 19, 5608;
( j) Y. Liu, Q.-L. Wang, Z. Chen, Q. Zhou, B.-Q. Xiong,
P.-L. Zhang and K.-W. Tang, Chem. Commun., 2019, 55,
12212.
Org. Lett., 2006, 4, 657; (i) H. B. Park, Y.-J. Kim, J. K. Lee, 10 (a) Z. Zhang, X.-J. Tang and W. R. Dolbier, Jr., Org. Lett.,
K. R. Lee and H. C. Kwon, Org. Lett., 2012, 19, 5002.
7 (a) W.-C. Yang, M.-M. Zhang and J.-G. Fenga, Adv. Synth.
Catal., 2020, 362, 4446; (b) C. R. Reddy, S. K. Prajapti,
K. Warudikar, R. Ranjan and B. B. Rao, Org. Biomol. Chem.,
2017, 15, 3130; (c) R. Song and Y. Xie, Chin. J. Chem., 2017,
35, 280; (d) X.-Y. Liu and Y. Qin, Acc. Chem. Res., 2019, 52,
1877.
2016, 18, 1048; (b) L. Yuan, S.-M. Jiang, Z.-Z. Li, Y. Zhu,
J. Yu, L. Li, M.-Z. Li, S. Tang and R.-R. Sheng, Org. Biomol.
Chem., 2018, 16, 2406; (c) C. Li, Y. Zhao, J. Zhou, X. Wang,
J. Hou, Y. Song, W. Liu and G. Han, Org. Biomol. Chem.,
2020, 18, 8376; (d) S. Tang, L. Yuan, Z.-Z. Li, Z.-Y. Peng,
Y.-L. Deng, L.-N. Wang, G.-X. Huang and R.-L. Sheng,
Tetrahedron Lett., 2017, 58, 2127; (e) K. Muranaka,
S. Ichikawa and A. Matsuda, J. Org. Chem., 2011, 76, 9278;
(f) G. Han, Y. Liu and Q. Wang, Org. Lett., 2014, 16, 3188.
8 (a) C. R. Reddy, R. Ranjan, S. K. Prajapti and K. Warudikar,
J. Org. Chem., 2017, 82, 6932; (b) F. Gao, C. Yang, G.-L. Gao,
L. Zheng and W. Xia, Org. Lett., 2015, 17, 3478; 11 (a) C. Zheng and S. L. You, ACS Cent. Sci., 2021, 7, 432;
(c) D. Yugandhar, S. Kuriakose, J. B. Nanubolu and
A. K. Srivastava, Org. Lett., 2016, 18, 1040;
(d) K. C. Nicolaou, D. J. Edmonda, A. Li and G. S. Tria,
Angew. Chem., Int. Ed., 2007, 46, 3942; (e) T. R. Ibarra-
Rivera, R. Gamez-Montano and L. D. Miranda, Chem.
Commun., 2007, 3, 3485; (f) X.-W. Liang, C. Zheng and
S.-L. You, Chem. – Eur. J., 2016, 22, 11918; (g) X. Zhang and
R. C. Larock, J. Am. Chem. Soc., 2005, 127, 12230;
(h) S. Chiba, L. Zhang and J.-Y. Lee, J. Am. Chem. Soc., 2010,
132, 7266; (i) Q. Yin and S.-L. You, Org. Lett., 2012, 13,
(b) Z.-P. Yang, R. Jiang, C. Zheng and S.-L. You, J. Am.
Chem. Soc., 2018, 140, 3114;For selected reviews on the Pd/
Ag-catalyzed oxidative reactions, see: (c) S. W. Youn and
Y. H. Kim, Org. Lett., 2016, 18, 6140; (d) C. Li, T. Yano,
N. Ishida and M. Murakami, Angew. Chem., Int. Ed., 2013,
52, 9801; (e) D. R. Stuart, E. Villemure and K. Fagnou,
J. Am. Chem. Soc., 2007, 129, 12072; (f) M. Miyasaka,
K. Hirono, T. Satoh and M. Miura, J. Org. Chem., 2010, 75,
5421; (g) S. Islam and I. Larrosa, Chem. – Eur. J., 2013, 19,
15093.
3526; ( j) Y. L. Tnay, C. Chen, Y. Y. Chua, L. Zhang and 12 For selected reviews on alkyl radicals that are generated by
S. Chiba, Org. Lett., 2012, 13, 3550.
the reaction of alkyl halides and Pd(0) via a SET process,
see: (a) S. Sumino and I. Ryu, Org. Lett., 2016, 18, 52;
(b) D. Kurandina, M. Rivas, M. Radzhabov and
V. Gevogyan, Org. Lett., 2018, 20, 357; (c) L. Sun, J.-H. Ye,
W.-J. Zhou, X. Zeng and D.-G. Yu, Org. Lett., 2018, 20, 3049;
(d) Z. Jiao, L. H. Lim, H. Hirao and J. S. Zhou, Angew.
Chem., Int. Ed., 2018, 57, 6294; (e) Y. Zou and J. Zhou,
Chem. Commun., 2014, 50, 3725; (f) K. S. Bloome,
R. L. McMahen and E. J. Alexanian, J. Am. Chem. Soc., 2011,
133, 20146; (g) G.-Z. Wang, R. Shang, W.-M. Cheng and
Y. Fu, J. Am. Chem. Soc., 2017, 139, 18307.
9 (a) L. Low-Beinart, X. Sun, E. Sidman and T. Kesharwani,
Tetrahedron Lett., 2013, 54, 1344; (b) C. R. Reddy,
U. Ajaykumar and D. H. Kolgave, J. Org. Chem., 2020, 85,
15521; (c) J. Wen, W. Wei, S. Xue, D. Yang, Y. Lou, C. Gao
and H. Wang, J. Org. Chem., 2015, 80, 4966; (d) C. R. Reddy,
D. H. Kolgave, M. Subbarao, M. Aila and S. K. Prajapti, Org.
Lett., 2020, 22, 5342; (e) P. Gao, W. Zhang and Z. Zhang,
Org. Lett., 2016, 18, 5820; (f) Y. Zhou, X. Zhang, Y. Zhang,
L. Ruan, J. Zhang, D. Zhang-Negrerie and Y. Du, Org. Lett.,
2017, 19, 150; (g) C.-S. Wang, T. Roisnel, P. H. Dixneuf and
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