Heterocyclization involving benzylic C(sp3)-H functionalization enabled by visible light photoredox catalysis

Article abstract of DOI:10.1039/c9cc04287c

A general and efficient method for heterocyclization involving benzylic C(sp³)-H functionalization enabled by visible light photoredox catalysis to access a wide range of structurally diverse oxygen as well as nitrogen heterocycles up to a gram scale is reported. The potential application of this new methodology is demonstrated by the total synthesis of (-)-codonopsinine and (+)-centrolobine. Herein it is proposed that selectfluor, unlike a fluorinating reagent, acts as an oxidative quencher and a hydrogen radical acceptor.

Full text of DOI:10.1039/c9cc04287c

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DOI: 10.1039/C9CC04287C
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Heterocyclization involving Benzylic C(sp3)–H Functionalization
Enabled by Visible Light Photoredox Catalysis
Ganesh Pandey,*aRamkrishna Lahaa,b and Pradip Kumar Mondala,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A general and efficient method of heterocyclization involving 1d) for N-heterocyclization7a-e and in the case of
benzylic C(sp3)-H functionalization enabled by visible light cycloetherification a separate directing group is required
photoredox catalysis to access a wide range of structurally diverse (Figure 1e).7f-g Although, these strategies certainly address the
oxygen as well as nitrogen heterocycles up to gram scale is regioselectivity issue, installation of appropriate directing group
reported. Potential application of this new methodology is and their removal require multistep sequences. Another unique
demonstrated by the total synthesis of (–)-codonopsinine and (+)- approach for N–heterocyclization involves oxidative coupling of
centrolobine. Herein it is proposed that selectfluor, unlike C, N–dianions in presence of a strong base and an oxidant
fluorination, acts an oxidative quencher and hydrogen radical (Figure 1f).3a,8 Nevertheless, the excess use of strong base
acceptor.
precludes the functional group tolerability.
Nitrogen and oxygen-containing heterocyclic scaffolds are
dominant structural motifs present in many biologically active
natural products and pharmaceuticals.1,2 Therefore, their
synthesis has been an attractive target of considerable interest
among synthetic organic chemists. Although, significant
progress has been made towards the advancement of this area,
majority of these reactions require multistep sequence or pre-
functionalized starting materials.3 For example, classically these
heterocyclizations were achieved via intra-molecular 1, 5-
hydrogen transfer followed by cyclization involving highly
reactive nitrogen or oxygen centered radical species to
construct pyrrolidine or tetrahydrofuran moieties respectively
(Figure 1a).4 On the other hand, transition metal catalyzed (Rh,
Ru, Co and Fe) intramolecular amination via nitrene insertion to
the C(sp3)–H bond has been extensively used as one of the most
powerful and efficient strategy for N–heterocyclization (Figure
1b).5 However, finding a suitable nitrene source, use of an
external oxidant and selectivity still remains a major issue
associated with this strategy. Intramolecular allylic amination
and etherification involving a π–allyl palladium complex is also
reported (Figure 1c).6 Directing group assisted transition metal
catalyzed C(sp3)–H functionalization is well documented, where
amine protecting group itself acts as a directing group (Figure
Previous works
b) Nitrene insertion into C(sp3)–H bond
a) Homolysis of Y-X bond
heat or h
TM
X
H
Y
Y
N
X
H
N
Y = NR, X = Cl
Y = O, X = Cl, I, NO
X = H2, N2, IAr
R2
R1
R1
R1
R1
c) Allylic C-H activation
Pd(II),oxidant
d) Directed C-N bond formation
TM
N
X
H
N
X=DG or EWG
Y=O or NTs
YH
R2
Y
R2
R1
R1
f) C,N-dianion oxidation
e) Directed C–O bond formation
n-BuLi
Pd(II)
H
N
N
I2 or PhSSPh
H
oxidant
R2
R2
DG
H
DG
OH
O
R1
R1
Present Work
g)
Photoredox
catalyis
Photoredox
catalyis
H
N
Y
R1
R1
O
R1
Y = OH
Y = NHR2
R2
Fig. 1 Intramolecular C(sp3–H) functionalization strategies
Despite the aforementioned elegant works, still there is a
compelling demand to develop a general and selective
heterocyclization strategy through C(sp3)–H functionalization to
synthesize various heterocycles, which must be devoid of
directing group, an oxidant, pre-oxidized substrate and harsh
reaction condition. To meet such a demanding goal, though
highly desirable, is a very challenging task (Figure 1g).
In the past decade, visible-light photoredox reaction involving
arene radical cation has led to the development of a number of
unprecedented C–X (X = N, O) bonds forming methodologies
through C(sp2)–H functionalization,9,10a while very few
a. Department of Chemistry, Institute of Science, Banaras Hindu University,
Varanasi-221005 (U. P.), India. E-mail: ganesh.pandey1@bhu.ac.in
b. RamkrishnaLaha and Pradip Kumar Mondal have contributed equally.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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advancements have been made through C(sp3)–H a range of photocatalysts, oxidative quenchers and bases at
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functionalization.10 Our own research interest in this area has room temperature in different solveDnOtsI: 10(f.1o0r39d/Ce9tCaCils0,428se7Ce
resulted in the benzylic C(sp3)–H functionalization for both Supporting Information). To our gratification, when 1a (1.0
inter- and intramolecular C–O bond formation as well as equiv) was irridiated in dry CH3CN for 24 h in the presence of
intermolecular C–N bond formation using cyanoaromatic as an 2.5 mol % of Ru(bpy)3(PF6)2 (5), 3.0 equiv of selectfluor (8) and
organophotoredox catalyst.11a,b However, these strategies
3.0 equiv of Na2HPO4, the desired cyclised product (4a) was
obtained in 74% isolated yield (Table 1, entry 1). Deviation from
standared conditions using different catalysts (entries 2 and 3),
base (entry 4), oxidative quencher (entry 5), solvent (entry 6)
and degassed condtion (entry 7) failed to deliver better results.
Controlled experiments justified the requirement of the light
source, photocatalyst and an oxidative quencher for this
cyclization reaction (entry 8). However, absence of a base led to
the formation of a complex reaction mixture and diminished the
yield of 4a significantly (entry 9).
+2
Cl
Cl
Cl
-
N
-
N
BF4
2BF4
N
N
N
N
N
2
N
N
10
8
F
2PF6
Ru
N
-
Ru(bpy)3(PF6)2 (5)
N
9
*
Ru2+
2BF4
N
SET
6
F
visible-light
photocatalysis
Ru3+
7
-HF
Y
H
SET
N
H
N
R
HAT
N
R
3
4
Ru2+
5
HY
MeO
R
MeO
MeO
2
MeO
-H
MeO
4c
R = Ts, , 70%
4e
R = Ts, , 55%
R = SO2Ph, , 60%
4a
R = Ts, , 74%
4d
R = SO2Ph, , 76%
4f
c
4b
R = SO2Ph, , 84%, (76%)
SET = single electron transfer
HAT = hydrogen atom transfer
Y
Ph
HY
NTs
Y = O, NR
N
R
1
MeO
MeO
N
Ph
O
R
4i
R = Ts, , 65%
4j
R = SO2Ph, , 68%
MeO
Fig. 2 Plausible catalytic cycle for heterocyclization
4g
R = Ts, , 56%
R = SO2Ph, , 60%
4k
, 58%
4h
n
Et
NTs
were unsuccessful for the N-heterocyclization reaction, albeit,
we have recently reported an intermolecular C(sp3)–H
amination using Ir(III) photocatalyst.11c,d Considering the
importance of heterocycles and impending general
methodology, we sought to evaluate a new strategy based on
C(sp3)–H functionalization using photoredox catalysis as shown
N
Et
Ts
N
Ts
MeO
4m
4n
MeO
MeO
, n = 1, 64%, dr = 2.2:1
, n = 2, 65%, dr = 2.9:1
4o
, 48%
4l
, 62%, dr = 2.2:1
Et
Et
NTs
NTs
N
O
in
Figure
2.
Herein,
wereport
a
general
Bn
MeO
MeO
MeO
d
p,
4
65%
4r
heterocyclizationstrategy which has also been successfully
applied in the natural product synthesis.
, 58%
4q
, 42%
Et
O
Bn
N
N
N
O
R
Ts
Ru(bpy)3(PF6)2 (2.5 mol%)
Selectfluor (3 equiv)
Na2HPO4 (3 equiv)
MeO
4u
R = Boc,
MeO
MeO
4v
, 78%, R = Cbz, , 77%
R = Ms, , 82%, R = Troc, , 80%
e
4t
, 55%
4s
, 38%
4w 4x
HN
Ts
N
Dry CH3CN ( 0.025 M)
Ts
blue LED ( = 454 nm)

Scheme 1. Synthesis of N-Heterocycles: (a) Reaction conditions: 1 (0.20
mmol), 5 (2.5 mol %), 8 (0.6 mmol) and base (0.6 mmol) in dry CH3CN
(8 mL) were irradiated at rt for 24 h using blue LED. (b) Isolated yield of
the product 4. (c) Reaction was performed in 2.1 g scale. (d) Reaction
time 2 h. (e) Reaction time 0.25 h.
MeO
MeO
rt, 24 h
1a
4a
Entry
1
2
3
4
5
6
7
8
Deviation from standard condition
none
Yield(%)b
74
69
74
trace
55
0
74
0
10
84
With this optimized reaction condition in hand, we then
examined the substrate scope over a wide range of N-protected
linear amines (1a-x) and found that desired cyclization
proceeded smoothly to give corresponding products (4a-ax)
withdifferent ring size and substitution pattern in 38-84%
isolated yields (Scheme 1). We also observed that the
cyclization proceeded more efficiently for the substrate with no
substitution at benzylic position (4a-d, 4i-j, and 4l-n) compared
to the substrate having an alkyl or aromatic substitution at the
Ru(bpy)3Cl2.6H2O instead of 5
(Ir[dF(CF3)ppy]2(dtbpy))PF6 instead of 5
K2CO3 instead of Na2HPO4
BrCCl3 instead of 8
DMSO instead of CH3CN
reaction mixture was degassed
in absence of light or catalyst or 8
in absence of Na2HPO4
9
10
1b instead of 1a
Table 1: Optimization of Reaction Conditions: (a) Reaction conditions: 1a (0.2 same position (4e-h and 4k). p–OPh group instead of p–OMe
mmol, 1 equiv), 5 (2.5 mol %), 8 (0.6 mmol, 3.0 equiv), base (0.6 mmol, 3.0 equiv),
solvent 8 mL, rt, blue LED, 24 h. (b) Isolated yield of 4a.
group on substrate was found to have no detrimental effect on
cyclization process and produced targeted products (4i and 4j)
in good yield. We have also synthesized more challenging
To validate our proposed hypothesis, N-tosyl amine (1a) was
first irradiated with visible light (λ = 454 nm, 3 W, blue LED) over
spirocyclic
derivative
(4k).However,
modest
2 | J. Name., 2012, 00, 1-3
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diastreoselectivtitywas observed in case of α-substituted amine of five-, six- and seven-membered cyclic ethers (4ah-ap) were
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derivatives (4l-n, drupto 2.9:1). In addition, isoindoline (4o), prepared in moderate to good yields (44D-7O2I:%1,0.S1c0h39e/mC9eC3C)0.4287C
tetrahydroisoquinoline (4p), azepane (4q) and oxazolidine (4t) To explore the potential application of this methodology,
derivatives were synthesized in satisfactory yield under racemic unnatural amino acid derivatives (11 and 12) were
identical condition.To our delight, the utility of this reaction was prepared in good yield by post modification of 4b and 4c by
further illustrated to prepare lactams (4r and 4s), which are oxidative cleavage of the electron-rich aromatic ring using
challenging targets and profound structural motifs in bioactive catalytic amountRuCl3 (Scheme 4).14
molecules, via direct C–H amidation within a very short period
of time.12 Effect of various N-protecting groups was examined.
We found amines with electron withdrawing group such as -
SO2Ph, -Ms, -Cbz, -Boc and -Troc reacted efficiently to produce
corresponding products (4b and 4u-x). Notably, this cyclization
proceeded smoothly in gram scale to deliver 4b in good yield.
()n
1. RuCl3, NaIO4
CH3CN/CCl4/H2O
()n
N
N
MeO2C
R
2. SOCl2, MeOH
R
MeO
4c
11
12
, R = Ts, n = 1, 65%
, R = SO2Ph, n = 2, 70%
, R = Ts, n = 1
4b
, R = SO2Ph, n = 2
Scheme 4. Synthesis of (±) Amino Acid Derivatives
O
O
S
O
S
O
O
S
O
O
N
N
H
N
H
Subsequently, we undertook the synthesis of highly
functionalized (-)-codonopsinine (15), isolated from Codonopsis
clematidea, which displays significant antibiotic and
hypotensive activities without affecting the central nervous
system.15a To this end, we synthesized pivotal intermediate 14
from enantiopure 13 in modest yield and diastereoselectivity
(dr = 1.9:1). Epoxidation of 14 using m-CPBA, followed by acid
mediated ring opening and finally LiAlH4 reduction gave (-)-
Codonopsinine (15) in 22% yield over 3 steps (Scheme 5).15b
O
O
H
MeO
MeO
MeO
R3
c
aa,
4
66%
4y
, 64%
R2
4z,
58%
O
O
S
O
R1
O
S
O
S
NH
O
O
N
H
N
H
O
O
MeO
MeO
MeO
, 68%,c R3 = CH2CH2Ph
, 66%,c R3 = CH2CH(CH3)2
60%,c R3 = CH2CH=CH2
4ad
4ae
4af,
4ag,
50%
4ab
4ac
, 55%, R1 = R2 = Me
, 60%,c R1 = H, R2 = Et
Scheme 2. Synthesis of cyclic sulfamidates: (a) Reaction conditions: 1
(0.2 mmol), 5 (2.5 mol %), 8 (0.6 mmol) and base (0.6 mmol) in CH3CN
(8 mL) were irradiated at rt for 18 h using blue LED. (b) Isolated yield of
the product 4. (c)dr> 20:1.
OH
1. m-CPBA
2. H2SO4
HO
Stand.
PMP
dioxane/H2O
N
NHCbz Cond'n
PMP
3. LiAlH4, THF
N
Cbz
13
This protocol was also amenable for the cyclization of various
sulfamate esters (Scheme 2, 4y-4ag, 50-68%, dr> 20:1), a source
of 1, 3-amino alcohols and related β-amino alcohols, generally
obtained via transition metal catalyzed nitrene insertion or
analogous reactions.5b,13 Interestingly, we observed both 1, 3-
cis isomer (4aa and4ad-af) and 1, 2-trans isomer (4ac) as a
single diastereomer. We were impressed withthe excellent
regioselectivity observed for 4ad-4af which otherwise is difficult
to achieve by other methods.13 Furthermore, an optically pure
product (4aa)was obtained in good yield and excellent
diastereoselectivity (dr> 20:1) from optically pure 1aa.
14,
55%
15,
MeO
22%
PMP = p-methoxy phenyl
(-)-Codonopsinine
dr = 1.9:1
Scheme 5. Total synthesis of (-)-Codonopsinine (15)
We also targeted the synthesis of antibacterial (2R, 6S)-(+)-
centrolobine (17),16 an oxygen containing heterocycle which
was isolated from centrolobiumrobustum,by direct photoredox
cyclization of 16 in excellent yield (93%, dr> 1.6:1).Isolation of
the major diastereomer followed by O-acetate deprotection
resulted (+)-centrolobine (17)in 85% yield (Scheme 6).16a
OH
OAc
1.stand. Cond'n
O
Ph
n
HO
16
n = 2
2. NaOH/MeOH
n = 2
O
O
O
17
, 85%
MeO
MeO
(+)-centrolobine
Ph
Et
MeO
O
4ah
n = 1,
, 68%
4ak,
4ao,
70 %
4al,
58%
Scheme 6. Total Synthesis of (+)-Centrolobine (17)
4ai
4aj
n = 2,
n = 3,
, 72%
, 44%
Et
n
O
To evaluate the possible mechanism of heterocyclization, we
performed some controlled experiments (Please see the
supporting information). Since substrate 1aq (without OMe)
has very high oxidation petential (Ep/2 = + 2.28 V SCE), electron
transfer(ET) to Ru(III)(E1/2III/II= + 1.32 V vs SCE) is difficult and in
case of substrate 1ar(m-OMe, Ep/2 = + 1.68 V vs SCE), thoguh ET
is feasible, the generated benylic carbocation intermediate (3)
is not stabilized due to lack of +R effect of -OMe group. Based
on the observations from the controlled experiment, we
propose that the reaction plausibly proceeds via single electron
O
O
MeO
MeO
4am
4an
MeO
4ap,
46%
, n = 1, 60%, dr = 1.6:1
, n = 2, 62%, dr = 1.5:1
64%
Scheme 3. Synthesis of Cyclic Ethers:(a) Reaction conditions: 1 (0.20
mmol), 5 (2.5 mol %), 8 (0.6 mmol) and base (0.6 mmol) in dry CH3CN
(8 mL) were irradiated at rt for 18 h using blue LED. (b) Isolated yield of
product 4.
After successful N-heterocyclization, we prepared a wide range
of cyclic ethers from corresponding linear alcohols.2a A number
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J. Name., 2013, 00, 1-3 | 3
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transfer (SET) from the excited Ru (II)* complex 6 (E1/2III/II*= –
0.85 V vs SCE) to selectfluor 8 (Ep/2 =+ 0.46 V vs SCE)17a,c
generating reduced selectfluorspecies 9 and Ru (III) (E1/2III/II= +
1.32 V vs SCE) which gets reduced to Ru (II) by oxidizing the
electron rich arene moiety 1 (1a, Ep/2 = + 1.59 V vs SCE) to
correspondingarene radical cation intermediate 2(for details
see Supporting Information). At this point, we believed that H-
abstraction by 9 from benzylic position of 2 led to the formation
of stable carbocation 3, which on cyclization with a tethered
nucleophile (–NHR or –OH) produced desired cyclized product 4
(Figure 2). It is worthy to mention that, selectfluor, unlike a
potential fluorinating17b-dreagent, acts as an efficient oxidative
quencher as well as hydrogen radical acceptor in this
reaction.17e
2005, 127, 14198; (e) J. V. Ruppel, R. M. Kamble, X. P. Zhang,
View Article Online
Org. Lett. 2007, 9, 4889; (f) Q. Nguyen, K. Sun, T. G. Driver, J.
Am. Chem. Soc. 2012, 134, 7262; (g) J.DLO. RI:o1i0z.e10n3,9M/C.9EC.CH0a4r2v8e7yC,
J. Du Bois, Acc. Chem. Res. 2012, 45, 911; (h) B. Bagh, D. L. J.
Broere, V. Sinha, P. F. Kuijpers, N. P. van Leest, B. de Bruin, S.
Demeshko, M. A. Siegler, J. I. van der Vlugt, J. Am. Chem. Soc,
2017, 139, 5117.
6
(a) S. E. Ammann, G. T. Rice, M. C. White, J. Am. Chem.
Soc. 2014, 136, 10834; (b) J. K. Fraunhoffer, M. C. White, J.
Am. Chem. Soc. 2007, 129, 7274.
7
(a) J. J. Neumann, S. Rakshit, T. Droge, F. Glorius, Angew.
Chem., Int. Ed. 2009, 48, 6892; (b) E. T. Nadres, O. Daugulis, J.
Am. Chem. Soc. 2012, 134, 7; (c) M. Yang, B. Su, Y. Wang, K.
Chen, X. Jiang, Y. F. Zhang, X. S. Zhang, G. Chen, Y. Cheng, Z.
Cao, Q. Y. Guo, L. Wang, Z. J. Shi, Nat. Commun. 2014, 5, 4707;
(d) X. Wu, K. Yang, Y. Zhao, H. Sun, G. Li, H. Ge, Nat. Commun.
2015, 6, 6462; (e) C. Yamamoto, K. Takamatsu, K. Hirano, M.
Miura, J. Org. Chem. 2016, 81, 7675; (f) S. J. Thompson, D. Q.
Thach, G. Dong, J. Am. Chem. Soc. 2015, 137, 11586; (g) H.
Wang, Y. Niu, G. Zhang, X. S. Ye, Tettahedron Lett. 2016, 57,
4544.
In conclusion, we have presented an unprecedented method for
both intramolecular benzylic C(sp3)–N and C(sp3)–O bond
forming reactions via visible light photoredox catalysis. This
mild and operationally simple protocol works well over a wide
range of structurally diverse five, six and seven membered
nitrogen as well as oxygen containing heterocycles in good to
excellent yields. Synthetic potential of this method has been
demonstrated by diastereoselective total synthesis of (–)-
codonopsinine (15) and(+)-centrolobine (17). Efforts are under
way to address further mechanistic details and extrapolation of
this work.
8
(a) A. Bisai, S. P. West, R. Sarpong, J. Am. Chem. Soc. 2008,
130, 7222.
9
(a) N. A. Romero, K. A. Margrey, N. E. Tay, D. A. Nicewicz,
Science. 2015, 349, 1326; (b) Y. W. Zheng, B. Chen, P. Ye, K.
Feng, W. Wang, Q. Y. Meng, L. Z. Wu, C. H. Tung, J. Am. Chem.
Soc. 2016, 138, 10080; (c) S. Das, P. Natarajan, B. Konig, Chem.
Eur. J. 2017, 23, 18161.
10 (a) H. Zhang, A. Lei, Asian J. Org. Chem. 2018, 7, 1164; (b)
L. C. Finney, L. J. Mitchell, C. J. Moody, Green Chem., 2018, 20,
2242.
11 (a) G. Pandey, S. Pal, R. Laha, Angew. Chem. Int. Ed. 2013,
52, 5146. (b) G. Pandey, R. Laha, Angew. Chem., Int. Ed. 2015,
54, 14875; (c) G. Pandey, R. Laha, D. Singh, J. Org. Chem. 2016,
81, 7161; (d) G. Pandey, D. Singh, R. Laha, Asian J. Org. Chem.
2017, 6, 469.
12 (a) S. Y. Hong, Y. Park, Y. Hwang, Y. B. Kim, M. H. Baik, S.
Chang, Science, 2018, 359, 1016. (b) C. Zhu, Y. Liang, X. Hong,
H. Sun, W. Y. Sun, K. N. Houk, Z. Shi, J. Am. Chem. Soc. 2015,
137, 7564.
G.P. thanks to DST, New Delhi for financial support (J.C. Bose
Fellowship), R. L. and P.K.M. thank to CSIR, New Delhi for award
of a research fellowship. We also thanks toProf. Atul Goel, CDRI,
Lucknow, India and Mr. S. Halder, BITS Pilani, Goa, for the CV and
UV analysis.
Conflicts of interest
The authors declare no competing financial interest.
13 (a) S. M. Paradine, J. R. Griffin, J. Zhao, A. L. Petronico, S.
M. Miller, M. C. White, Nat. Chem. 2015, 7, 1. (b) M. Huang,
T. Yang, J. D. Paretsky, J. F. Berry, J. M. Schomaker, J. Am.
Chem. Soc. 2017, 139, 17376.
14 P. H. J. Carlsen, T. Katsuki, V. S. Martin, K. B. Sharpless, J.
Org. Chem. 1981, 46, 3936.
15 (a) M. Lingamurthy, Y. Jagadeesh, K. Ramakrishna, B. V.
Rao, J. Org. Chem. 2016, 81, 1367. (b) M. Yamaguchi, D.
Itagaki, H. Ueda, H. Tokuyama, J. Antibiot. (Tokyo). 2016, 69,
253.
16 (a) F. Rogano, P. Rüedl, Helv. Chim. Acta 2010, 93, 1281.
(b) J. R. Vyvyan, H. E. Longworth, S. K. Nguyen, Synlett 2016,
27, 2221.
17 (a) M. Rueda-Becerril, O. Mahé, M. Drouin, M. B.
Majewski, J. G. West, M. O. Wolf, G. M. Sammis, J. F. Paquin,
J. Am. Chem. Soc. 2014, 136, 2637. (b) A. R. Mazzotti, M. G.
Campbell, P. Tang, M. J. Murphy, T. Ritter, J. Am. Chem. Soc.
2013, 135, 14012. (c) S. Ventre, F. R. Petronijevic, D. W. C.
MacMillan, J. Am. Chem. Soc. 2015, 137, 5654. (d) J. B. Xia, C.
Zhu, C. Chen, J. Am. Chem. Soc. 2013, 135, 17494. (e) S. Wang,
J. Liu, L. Niu, H. Yi, C. W. Chiang, and A. J. Lei, Photochem.
Photobiol. A: Chem. 2018, 355, 120.
References
1
(a) R. Hili, A. K. Yudin, Nat. Chem. Biol. 2006, 2, 284; (b) A.
H. Lipkus, Q. Yuan, K. A. Lucas, S. A. Funk, W. F. Bartelt, R. J.
Schenck, A. J. Trippe, J. Org. Chem. 2008, 73, 4443.
2
(a) A. Lorente, J. Lamariano-Merketegi, F. Albericio, M.
Álvarez, Chem. Rev. 2013, 113, 4567.
(a) J. L. Jeffrey, R. Sarpong, Chem. Sci. 2013, 4, 4092; (b) T.
3
A. Ramirez, B. Zhao, Y. Shi, Chem. Soc. Rev. 2012, 41, 931; (c)
F. Collet, C. Lescot, P. Dauban, Chem. Soc. Rev. 2011, 40, 1926;
(d) J. W. W. Chang, T. M. U. Ton, P. W. H. Chan, Chem. Rec.
2011, 11, 331–357; (e) T. G. Driver, Nat. Chem. 2013, 5, 736;
(f) O. V. Zatolochnaya, V. Gevorgyan, Nat. Chem. 2014, 6, 661;
(g) B. Liu, B. F. Shi, Tetrahedron Lett. 2015, 56, 15; (h) Y. Park,
Y. Kim, S. Chang, Chem. Rev. 2017, 117, 9247.
4
(a) A. W. Hofmann, Ber. Dtsch. Chem. Ges. 1883, 16, 558;
(b) A. W. Hofmann, Ber. Dtsch. Chem. Ges. 1885, 18, 5; (c) G.
Majetich, K. Wheless, Tetrahedron 1995, 51, 7095; d) Ž. J.
Čeković, Serb. Chem. Soc. 2005, 70, 287.
5
a) C. G. Espino, J. Du Bois, Angew. Chem., Int. Ed. 2001, 40,
598–600; (b) C. G. Espino, P. M. When, J. Chow, J. Du Bois, J.
Am. Chem. Soc. 2001, 123, 6935; (c) J. L. Liang, S. X. Yuan, J. S.
Huang, W. Y. Yu, C. M. Che, Angew. Chem., Int. Ed. 2002, 41,
3465; (d) H. Lebel, K. Huard, S. Lectard, J. Am. Chem. Soc.
4 | J. Name., 2012, 00, 1-3
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