Iminoxyl Radical-Promoted Oxycyanation and Aminocyanation of Unactivated Alkenes: Synthesis of Cyano-Featured Isoxazolines and Cyclic Nitrones

Article abstract of DOI:10.1021/acs.orglett.7b00826

A novel and facile approach to vicinal oxycyanation and aminocyanation of internal unactivated alkenes is developed. This method utilizes the dichotomous reactivity of iminoxyl radical derived from the initiation of β,γ- and γ,δ-unsaturated ketoximes to provide the general difunctionalization of internal alkenes using tert-butyl hydroperoxide (TBHP) as the environmentally friendly oxidant, CuCN as the commercially available cyanating reagent, and pentamethyldiethylenetriamine (PMDETA) as the ligand. By using this protocol, a series of useful cyano-featured isoxazolines and cyclic nitrones were efficiently prepared.

Full text of DOI:10.1021/acs.orglett.7b00826

Letter
pubs.acs.org/OrgLett
Iminoxyl Radical-Promoted Oxycyanation and Aminocyanation of
Unactivated Alkenes: Synthesis of Cyano-Featured Isoxazolines and
Cyclic Nitrones
Fei Chen, Fei-Fei Zhu, Man Zhang, Rui-Hua Liu, Wei Yu, and Bing Han*
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou,
730000, P. R. China
S
* Supporting Information
ABSTRACT: A novel and facile approach to vicinal oxy-
cyanation and aminocyanation of internal unactivated alkenes
is developed. This method utilizes the dichotomous reactivity
of iminoxyl radical derived from the initiation of β,γ- and γ,δ-
unsaturated ketoximes to provide the general difunctionaliza-
tion of internal alkenes using tert-butyl hydroperoxide (TBHP)
as the environmentally friendly oxidant, CuCN as the commercially available cyanating reagent, and pentamethyldiethylene-
triamine (PMDETA) as the ligand. By using this protocol, a series of useful cyano-featured isoxazolines and cyclic nitrones were
efficiently prepared.
Scheme 1. Radical Mediated Oxycyanation and
Aminocyanation of Alkenes
he cyano group as an important functional group not only
1
Tcan undergo manifold valuable transformations but also
exists widely in bioactive natural products and pharmaceut-
icals.2 In particular, the cyano-featured five-membered hetero-
cycles have found various applications as fine chemicals.3 For
example, compounds I and II are synthetic molecules with
antibacterial activity.4,5 Compound III is an important
intermediate for the synthesis of amathaspiramides (Figure 1).6
aminocyanation of aryl alkenes.12c Despite these elegant studies
toward this end, however, the advancement is far from meeting
the synthetic demand, and there are still much that remains to
be explored.
Figure 1. Bioactive molecules with cyano substituted heterocycle unit.
Thus, the efficient introduction of cyano group into organic
molecules has drawn much attention from chemists and
pharmacologists.7 Over the past decades, studies in this line
are mainly focused on the nucleophilic substitution of primary
alkyl halides with cyanides8 and transition metal catalyzed
C(sp2)−H and C(sp3)−H bond cyanation,9,10 while inves-
tigations on direct cyanation of alkenes are relatively less
reported.11
Considering that alkenes are broadly available chemicals, the
vicinal oxycyanation and aminocyanation of alkenes are
attractive strategies to introduce the CN group as well as the
O/N atom into organic molecules.12 Recently, a few radical-
mediated approaches have been reported based on these
strategies. For instance, in 2013 Alexanian’s group developed an
amidoxyl radical promoted intra-/intermolecular oxycyanation
of unactivated alkenes (Scheme 1a).12b Very recently, Liu et al.
disclosed an amide radical-involved asymmetric intermolecular
In continuation of our research on the difunctionalization of
alkenes,13 herein we present a new and efficient iminoxyl
radical-promoted protocol14 for the oxycyanation and amino-
cyanation of internal unactivated alkenes by using β,γ- and γ,δ-
unsaturated ketoximes as readily available substrates, CuCN as
the cyanating reagent, and TBHP as the oxidant. Consequently,
the structurally important cyano-featured isoxazolines and
cyclic nitrones were facilely synthesized. This strategy not
only presents the first example of iminoxyl radical-participated
vicinal oxycyanation and aminocyanation of unactivated alkenes
but also attains a direct radical cyclization leading to structurally
important cyano-featured isoxazolines and cyclic nitrones.
Received: May 8, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b00826
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
ab
,
We commenced our study by stirring 2,2-dimethyl-1-
phenylbut-3-en-1-one oxime (1a) with CuCN (2.5 equiv) in
acetonitrile using TBHP (3.0 equiv) as the oxidant and diamine
L1 (2.5 equiv) as the ligand at room temperature for 12 h
under Ar. To our delight, the desired oxycyanation product 2a
was obtained in 62% yield (Table 1, entry 1). Screening other
Scheme 2. Scope of Unsaturated Oximes
a
Table 1. Optimization of the Reaction Conditions
b
entry
CN source
ligand
solvent
yield (%)
1
2
3
4
5
6
7
8
CuCN (2.5 equiv)
CuCN (2.5 equiv)
CuCN (2.5 equiv)
CuCN (2.5 equiv)
CuCN (2.5 equiv)
CuCN (2.5 equiv)
CuCN (2.5 equiv)
CuCN (2.5 equiv)
CuCN (3.0 equiv)
CuCN (2.5 equiv)
CuCN (2.0 equiv)
CuCN (2.5 equiv)
TMSCN (2.5 equiv)
TsCN (2.5 equiv)
L1
L2
L3
L4
L5
L2
L2
L2
L2
L2
L2
L2
L2
L2
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
DMF
62
70
47
3
8
33
34
trace
61
44
64
53
17
12
DMSO
toluene
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
c
9
d
10
e
11
f
12
g
13
h
14
a
All reactions were carried out by using 1a (0.3 mmol), CN source,
ligand (2.5 equiv), TBHP (70% aqueous, 3.0 equiv), solvent (2 mL) at
b
c
rt under Ar (1 atm) for 12 h, except as noted. Isolated yield. L2 (3.0
d
equiv) and TBHP (3.5 equiv) were used. L2 (3.0 equiv) was used.
L2 (2.0 equiv) and TBHP (2.5 equiv) were used. L2 (2.0 equiv) was
used. Cu(OAc)2 (0.2 equiv), L2 (0.2 equiv), and TBHP (2.0 equiv)
were used. Cu(OAc)2 (0.2 equiv), L2 (0.2 equiv), and TBHP (1.5
a
e
f
All reactions run in CH3CN (2 mL) using 1 (0.3 mmol), CuCN
g
(0.75 mmol), L2 (0.75 mmol), and TBHP (0.9 mmol) at rt under Ar
b
c
h
(1 atm) for 12 h. Isolated yields are shown. 1a (8 mmol) was used,
d
and the corresponding product 2a was obtained in 1.112 g. The
equiv) were used.
configuration of diastereomer was determined by coupling constants
of H NMR and NOE.
1
ligands such as triamine L2, tetraamine L3, 1,1′-bipyridine L4,
and 1,10-phen L5 revealed that L2 was the best ligand and the
yield of 2a was further improved to 70% (Table 1, entries 2−5).
No better yield of 2a was obtained when other solvents such as
DMF, DMSO, and toluene were used (Table 1, entries 6−8). A
further increase or decrease of the usage amount of CuCN, L2,
and TBHP did not provide a better result (Table 1, entries 9−
12). In addition, other cyanating reagents such as TMSCN and
TsCN were also tested in the reaction under Cu(OAc)2
catalyzed conditions, but they were found to be inferior
compared with CuCN (Table1, entries 13−14). Other catalytic
systems by using a variety of copper salts, CN-sources, and
oxidants were explored as well; however, no positive result was
obtained (see Supporting Information for detail).
With the optimized conditions in hand (Table 1, entry 2),
the scope of the reaction with various β,γ- and γ,δ-unsaturated
ketoximes was investigated, and the result is summarized in
Scheme 2. First, aryl and alkyl substituted β,γ-unsaturated
ketoximes 1a−v were explored. Phenyl substituted ketoximes
with a range of electronic properties participated well in the
reaction, affording the oxycyanation products 2a−j in good
yields. The structure of 2c was confirmed by single-crystal X-ray
analysis (see SI). Notably, the tandem reaction could be easily
carried out on a gram scale without difficulty, as demonstrated
in the case of 2a. Naphthalenyl- and thiophene-substituted
ketoximes were also suitable for the process, providing the
corresponding products 2k and 2l in good yields. Alkyl such as
phenethyl, n-hexyl, and cyclohexyl incorporated ketoximes were
also good candidates for the transformation, which can be
converted into the desired products 2m−o in 56−70% yields.
In addition, aryl substituted β,γ-unsaturated ketoximes without
a gem-dimethyl group were also examined in the reaction, and
the corresponding products 2p−s were obtained in moderate
to good yields. Significantly, this oxycyanation approach is
applicable to 1,1-disubstituted alkenes, as demonstrated in the
case of 2t. When the cyclohexene moiety was incorporated in
the β,γ-unsaturated ketoxime, as in the case of 1u, the reaction
gave the oxycyanation product 2u in 18% yield, accompanied
by the isoxazoline-fused cyclohexene 2u′ and cyclohexane 2u″
in 20% and 16% yields, respectively. When the ketoxime 1v was
used as the substrate, however, the reaction did not yield the
expected oxycyanation product 2v; instead, compound 2v′ was
obtained in a yield of 38%. Obviously, the secondary and
tertiary carbon-centered radicals were inclined to undergo
elimination and gave the corresponding olefins in this
circumstance.15 Next, we shifted our attention to γ,δ-
B
DOI: 10.1021/acs.orglett.7b00826
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
unsaturated counterparts to see if the latter could also undergo
aminocyanation through a N atom 5-exo-trig cyclization16 as
displayed in our previous work.13a−d Gratifyingly, a series of
aryl substituted γ,δ-unsaturated ketoximes participated
smoothly in the reaction, delivering the desired aminocyanation
products 2w−ab in moderate yields.
To further investigate the applicability of this protocol, other
cuprous salts such as CuCl, CuBr, and CuI were also allowed to
react with 1a, and the corresponding oxyhalogenation products
3−5 were obtained in 71−74% yields (Scheme 3). Moreover,
(Scheme 5, eq 2).15a These results demonstrated clearly that
the initiation step is the generation of the iminoxyl radical
which is involved in the subsequent oxycyanation and
aminocyanation process.
Based on the experimental results and the aforementioned
control experiments, a proposed mechanism for the iminoxyl
radical-promoted oxycyanation and aminocyanation is drawn in
Figure 2. First, TBHP reacts with CuI species A to produce CuII
ab
,
Scheme 3. Oxyhalogenation of Unactivated Alkenes
Figure 2. Proposed mechanism.
a
All reactions run in CH3CN (2 mL) using 1a (0.3 mmol), CuX (0.75
mmol), L2 (0.75 mmol), and TBHP (0.9 mmol) at rt under Ar (1
b
c
atm) for 12 h. Isolated yields. Cu(OAc)2 (0.2 equiv), L2 (0.3 equiv),
KSCN (2.5 equiv), and TBHP (2.0 equiv) were used.
species B and t-BuO radical, and the latter then initiates oxime
1 to an iminoxyl radical via a hydrogen atom abstraction
(HAT) process. The formed iminoxyl radical possesses an
electronic structure with the single-electron spin density
delocalized on both the O- and N-atom (resonance structures
C and D),13a−d and thus it can undergo dichotomous O- and
N-atom 5-exo-trig radical cyclization depending on the position
of the tethered alkene, yielding the formed C-centered radicals
E and F, respectively. Subsequently, the C-centered radical E or
F reacts with CuII species B to form CuIII intermediate G or
H.10h,11e Finally, intermediate G or H undergoes reductive
elimination to furnish the desired cyanation product 2 and the
cuprous species I.
when 1a reacted with KSCN utilizing Cu(OAc)2 as the catalyst,
the desired thiocyano substituted isoxazoline 6 was also
acquired in 30% yield along with 7 in 23% yield.
The cyano group is a versatile functional group that can be
exploited in synthetically useful transformations. In this context,
products 2 serve as precursors for other isoxazoline derivatives.
For instance, compound 2a could be easily converted to the
carboxylic acid 8 and amide 9 in excellent yields by treatment
with an acid and a base, respectively (Scheme 4).
Scheme 4. Follow-up Transformations of 2a
In conclusion, a novel, facile, and efficient approach for the
oxycyanation and aminocyanation of unactivated alkenes has
been successfully developed. This method features easily
accessible substrates, commercially available and inexpensive
reagents, and mild conditions. By using this protocol,
structurally important cyano-substituted isoxazolines and cyclic
nitrones can be readily synthesized from unsaturated ketoximes.
To the best of our knowledge, the present study represents the
first example of iminoxyl radical-promoted oxycyanation and
aminocyanation of unactive alkenes. Further studies on the
cyanation of alkenes and more iminoxyl radical-involved
reactions are in progress in our laboratory.
To confirm that the iminoxyl radical was involved in the
reaction, the control experiments were conducted as shown in
Scheme 5. When the radical scavenger 2,2,6,6-tetramethyl-1-
Scheme 5. TEMPO Scavenging and Radical Probe
Experiments
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.7b00826.
Detailed experimental procedures and spectral data for
all products (PDF)
Crystallographic data for the compound 2c (CIF)
piperidinyl-oxy (TEMPO) was added in the reaction system,
the oxycyanation was almost completely inhibited and the
TEMPO-trapped isoxazoline 10 was obtained in 95% yield
(Scheme 5, eq 1). When ketoxime 11 was subjected to the
standard conditions, the anticipated ring-opening cyanation
product 12 was obtained in 31% yield along with the ring-
opening/elimination product 1,3-diene 13 in 25% yield
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: hanb@lzu.edu.cn.
C
DOI: 10.1021/acs.orglett.7b00826
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
ORCID
Letter
(e) Kamijo, S.; Hoshikawa, T.; Inoue, M. Org. Lett. 2011, 13, 5928−
5931. (f) Ma, L.; Chen, W.; Seidel, D. J. Am. Chem. Soc. 2012, 134,
15305−15308. (g) Ushakov, D. B.; Gilmore, K.; Kopetzki, D.;
McQuade, D. T.; Seeberger, P. H. Angew. Chem., Int. Ed. 2014, 53,
557−561. (h) Zhang, W.; Wang, F.; McCann, S. D.; Wang, D.; Chen,
P.; Stahl, S. S.; Liu, G. Science 2016, 353, 1014−1018.
Bing Han: 0000-0003-0507-9742
Notes
The authors declare no competing financial interest.
(11) (a) Pinto, A.; Jia, Y.; Neuville, L.; Zhu, J. Chem. - Eur. J. 2007,
13, 961−967. (b) He, Y.-T.; Li, L.-H.; Yang, Y.-F.; Zhou, Z.-Z.; Hua,
H.-L.; Liu, X.-Y.; Liang, Y.-M. Org. Lett. 2014, 16, 270−273. (c) Liang,
Z.; Wang, F.; Chen, P.; Liu, G. J. Fluorine Chem. 2014, 167, 55−60.
(d) Fang, X.; Yu, P.; Morandi, B. Science 2016, 351, 832−836.
(e) Wang, F.; Wang, D.; Wan, X.; Wu, L.; Chen, P.; Liu, G. J. Am.
Chem. Soc. 2016, 138, 15547−15550. (f) Zhao, W.; Montgomery, J. J.
Am. Chem. Soc. 2016, 138, 9763−9766.
(12) (a) Yamasaki, S.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc.
2001, 123, 1256−1257. (b) Quinn, R. K.; Schmidt, V. A.; Alexanian, E.
J. Chem. Sci. 2013, 4, 4030−4034. (c) Wang, D.; Wang, F.; Chen, P.;
Lin, Z.; Liu, G. Angew. Chem., Int. Ed. 2017, 56, 2054−2058.
(13) (a) Han, B.; Yang, X.-L.; Fang, R.; Yu, W.; Wang, C.; Duan, X.-
Y.; Liu, S. Angew. Chem., Int. Ed. 2012, 51, 8816−8820. (b) Yang, X.-
L.; Chen, F.; Zhou, N.-N.; Yu, W.; Han, B. Org. Lett. 2014, 16, 6476−
6479. (c) Peng, X.-X.; Deng, Y.-J.; Yang, X.-L.; Zhang, L.; Yu, W.; Han,
B. Org. Lett. 2014, 16, 4650−4653. (d) Liu, R.-H.; Wei, D.; Han, B.;
Yu, W. ACS Catal. 2016, 6, 6525−6530. (e) Duan, X.-Y.; Yang, X.-L.;
Fang, R.; Peng, X.-X.; Yu, W.; Han, B. J. Org. Chem. 2013, 78, 10692−
10704. (f) Duan, X.-Y.; Zhou, N.-N.; Fang, R.; Yang, X.-L.; Yu, W.;
Han, B. Angew. Chem., Int. Ed. 2014, 53, 3158−3162.
(14) (a) Liu, Y.-Y.; Yang, J.; Song, R.-J.; Li, J.-H. Adv. Synth. Catal.
2014, 356, 2913−2918. (b) Zhang, W.; Su, Y.; Wang, K.-H.; Wu, L.;
Chang, B.; Shi, Y.; Huang, D.; Hu, Y. Org. Lett. 2017, 19, 376−379.
(15) (a) Kochi, J. K.; Bacha, J. D. J. Org. Chem. 1968, 33, 2746−2754.
(b) Faulkner, A.; Race, N. J.; Scott, J. S.; Bower, J. F. Chem. Sci. 2014,
5, 2416−2421. (c) Xiong, P.; Xu, F.; Qian, X.-Y.; Yohannes, Y.; Song,
J.; Lu, X.; Xu, H.-C. Chem. - Eur. J. 2016, 22, 4379−4383.
(16) For recent reviews on O- and N-centered radicals, see:
(a) Chen, J.-R.; Hu, X.-Q.; Lu, L.-Q.; Xiao, W.-J. Chem. Soc. Rev. 2016,
45, 2044−2056. (b) Xiong, T.; Zhang, Q. Chem. Soc. Rev. 2016, 45,
3069−3087. (c) Zhang, J.; Chen, Y. Huaxue Xuebao 2017, 75, 41−48.
For selected examples, see: (d) Hu, X.-Q.; Chen, J.-R.; Wei, Q.; Liu,
F.-L.; Deng, Q.-H.; Beauchemin, A. M.; Xiao, W.-J. Angew. Chem., Int.
Ed. 2014, 53, 12163−12167. (e) Hu, X.-Q.; Chen, J.; Chen, J.-R.; Yan,
D.-M.; Xiao, W.-J. Chem. - Eur. J. 2016, 22, 14141−14146. (f) Lu, H.;
Chen, Q.; Li, C. J. Org. Chem. 2007, 72, 2564−2569. (g) Yuan, X.; Liu,
K.; Li, C. J. Org. Chem. 2008, 73, 6166−6171. (h) Li, Z.; Song, L.; Li,
C. J. Am. Chem. Soc. 2013, 135, 4640−4643.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(21422205, 21272106, and 21632001), the Program for New
Century Excellent Talents in University (NCET-13-0258), the
Changjiang Scholars and Innovative Research Team in
University (IRT-15R28), the “111” project, and the Funda-
mental Research Funds for the Central Universities (lzujbky-
2016-ct02 and lzujbky-2016-ct08) for financial support.
REFERENCES
■
(1) (a) The Chemistry of the Cyano Group; Rappoport, Z., Ed.;
Interscience: London, 1970. (b) Larock, R. C. Comprehensive Organic
Transformations: A Guide to Functional Group Preparations; Wiley-
VCH: New York, 1989.
(2) (a) Fleming, F. F. Nat. Prod. Rep. 1999, 16, 597−606. (b) Enders,
D.; Shilvock, J. P. Chem. Soc. Rev. 2000, 29, 359−373.
(3) (a) Hamada, Y.; Kawai, A.; Kohno, Y.; Hara, O.; Shioiri, T. J. Am.
Chem. Soc. 1989, 111, 1524−1525. (b) Gombos, Z.; Nyitrai, J.;
́
Kolonits, P.; Kajtar-Peredy, M. J. Chem. Soc., Perkin Trans. 1 1989, 1,
1915−1921. (c) Arnold, M. A.; Day, K. A.; Duron
́
, S. G.; Gin, D. Y. J.
Am. Chem. Soc. 2006, 128, 13255−13260.
(4) Jayashankara, B.; Rai, K. M. L. E-J. Chem. 2008, 5, 370−376.
(5) Carcanague, D. R.; Gravestock, M. B.; Hales, N. J.; Hauck, S. I.;
Weber, T. P. PCT Int. Appl. WO 2004048392A1 20040610.
(6) O’Connor, M.; Sun, C.; Lee, D. Angew. Chem., Int. Ed. 2015, 54,
9963−9966.
(7) For reviews, see: (a) Wang, T.; Jiao, N. Acc. Chem. Res. 2014, 47,
1137−1145. (b) Yu, J.-T.; Teng, F.; Cheng, J. Adv. Synth. Catal. 2017,
359, 26−38. For recent selected examples, see: (c) Qin, C.; Jiao, N. J.
Am. Chem. Soc. 2010, 132, 15893−15895. (d) Anbarasan, P.;
Neumann, H.; Beller, M. Angew. Chem., Int. Ed. 2011, 50, 519−522.
(e) Shu, Z.; Ye, Y.; Deng, Y.; Zhang, Y.; Wang, J. Angew. Chem., Int. Ed.
2013, 52, 10573−10576. (f) Wang, T.; Jiao, N. J. Am. Chem. Soc. 2013,
135, 11692−11695. (g) Reeves, J. T.; Malapit, C. A.; Buono, F. G.;
Sidhu, K. P.; Marsini, M. A.; Sader, C. A.; Fandrick, K. R.; Busacca, C.
A.; Senanayake, C. H. J. Am. Chem. Soc. 2015, 137, 9481−9488.
(h) Ratani, T. S.; Bachman, S.; Fu, G. C.; Peters, J. C. J. Am. Chem. Soc.
2015, 137, 13902−13907. (i) Wu, Q.; Luo, Y.; Lei, A.; You, J. J. Am.
Chem. Soc. 2016, 138, 2885−2888. (j) Le Vaillant, F.; Wodrich, M. D.;
Waser, J. Chem. Sci. 2017, 8, 1790−1800.
(8) (a) Mowry, D. T. Chem. Rev. 1948, 42, 189−283. (b) Chiappe,
C.; Pieraccini, D.; Saullo, P. J. Org. Chem. 2003, 68, 6710−6715.
(9) For reviews, see: (a) Kim, J.; Kim, H. J.; Chang, S. Angew. Chem.,
Int. Ed. 2012, 51, 11948−11959. (b) Ping, Y.; Ding, Q.; Peng, Y. ACS
Catal. 2016, 6, 5989−6005. For recent selected examples, see:
(c) Gong, T.-J.; Xiao, B.; Cheng, W.-M.; Su, W.; Xu, J.; Liu, Z.-J.; Liu,
L.; Fu, Y. J. Am. Chem. Soc. 2013, 135, 10630−10633. (d) Yu, D.-G.;
́ ́
Gensch, T.; de Azambuja, F.; Vasquez-Cespedes, S.; Glorius, F. J. Am.
Chem. Soc. 2014, 136, 17722−17725. (e) Shu, Z.; Ji, W.; Wang, X.;
Zhou, Y.; Zhang, Y.; Wang, J. Angew. Chem., Int. Ed. 2014, 53, 2186−
2189. (f) Yang, Y.; Buchwald, S. L. Angew. Chem., Int. Ed. 2014, 53,
8677−8681. (g) Li, J.; Ackermann, L. Angew. Chem., Int. Ed. 2015, 54,
3635−3638. (h) Yang, Y.; Liu, P. ACS Catal. 2015, 5, 2944−2951.
(i) Zhu, Y.; Zhao, M.; Lu, W.; Li, L.; Shen, Z. Org. Lett. 2015, 17,
2602−2605. (j) McManus, J. B.; Nicewicz, D. A. J. Am. Chem. Soc.
2017, 139, 2880.
(10) (a) North, M. Angew. Chem., Int. Ed. 2004, 43, 4126−4128.
(b) Murahashi, S.-I.; Komiya, N.; Terai, H. Angew. Chem., Int. Ed.
2005, 44, 6931−6933. (c) Murahashi, S.-I.; Nakae, T.; Terai, H.;
Komiya, N. J. Am. Chem. Soc. 2008, 130, 11005−11012. (d) Tajima,
T.; Nakajima, A. J. Am. Chem. Soc. 2008, 130, 10496−10497.
D
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