Visible-light-promoted intramolecular C-H amination in aqueous solution: Synthesis of carbazoles

Article abstract of DOI:10.1039/c7gc03392c

An effective and operationally simple protocol is reported for the synthesis of versatile carbazoles. With water as a co-solvent, visible-light rather than various metals is used to facilitate the conversion of readily available 2-azidobiphenyls under mild conditions. Various functionalized bioactive natural alkaloids, such as glycoborine, clausine C, clausine L, clausine H and clauszoline K, were synthesized efficiently with nitrogen as a sole byproduct. The reaction could be performed in water, acidic or alkaline buffer solutions, showing its potential for applications in biochemistry.

Full text of DOI:10.1039/c7gc03392c

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: L. Yang, Y. Zhang,
X. Zou, H. Lu and G. Li, Green Chem., 2018, DOI: 10.1039/C7GC03392C.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 6
View Article Online
DOI: 10.1039/C7GC03392C
Green Chemistry
PAPER
Visible-Light-Promoted Intramolecular C–H Amination in Aqueous
Solution: Synthesis of Carbazoles
Lizheng Yang,a Yipin Zhang,a Xiaodong Zou,a Hongjian Lu*a and Guigen Lia,b
Received 00th January 20xx,
Accepted 00th January 20xx
An effective and operationally simple protocol is reported for the synthesis of versatile carbazoles. With water as co-
solvent, visible-light rather than various metals is used to facilitate conversion of readily available 2-azidobiphenyls under
mild conditions. Various functionalized bioactive natural alkaloids, such as glycoborine, clausine C, clausine L, clausine H
and clauszoline K were synthesized efficiently with nitrogen as sole byproduct. The reaction could be performed in water,
DOI: 10.1039/x0xx00000x
www.rsc.org/
acidic
or
alkaline
buffer
solutions,
showing
its
potential
for
applications
in
biochemistry.
CHO
OMe
Me
Introduction
CO2Me
OMe
MeO
N
The carbazole structural unit occurs in a large number of
biologically active natural and synthetic compounds,
pharmaceutical ingredients,1 and organic functional materials 2
(Figure 1). Protocols to access these N-heterocycles have relied
O
H
N
H
N
H
Furostifoline
Clausine H
Atanisatin
Me
C18H17
N
MeO
Ph
N
on transformations of pre-existing functional groups,1a-c,
3
Ph
N
N
N
H
H
which can result in some unnecessary steps to generate the
functionalized starting materials. Recent efforts in the
synthesis of carbazoles to circumvent this functional group
manipulation have made great achievements.3,4 One of the
simplest and most straightforward approaches is the catalytic
dehydrogenative C-H/N-H coupling of 2-aminobiphenyls.5
Either transition-metal catalysts or oxidants are necessary,
which reduces the functional group tolerance due to the tight
coordination ability of transition metals or the further
oxidation reactions.
C18H17
3,9-disubstituted indolo[3,2-b] carbazole
Me
Glycoborine
Ellipticine
Figure 1. The carbazole motif in biologically active alkaloids and functional
materials
gas as the sole by-product. Thus, intramolecular C−H
amination of 2-azidobiphenyls has become one of most
important green methods for the synthesis of N−H carbazoles
(Scheme 1A).7-11 Through intrinsically prone to decomposition,
2-azidobiphenyls can be directly transformed into carbazoles
at high temperature but this wastes power and has low
functional group tolerance (Method a).7 Decomposition by
means of UV8 and laser flash9 irradiation have also been
reported, but these publications focused on mechanistic
studies and failed to put the method into practice because of
the impediments of the harsh reaction conditions, unavoidable
side products like diazo and ring-opened compounds (Method
b). Recently, various transition-metal catalytic methods
instead of high temperature heating or UV have been well
developed but any noble metal must be carefully removed
from the final product prior to biological studies and the tight
coordination ability of transition metals reduces the functional
group tolerance (Method c).10 In our continuing research on
C−H aminaꢀon reacꢀons12 with water as solvent,10h,13 water
plays a unique role, including promotion of C−H acꢀvaꢀon,13
assisting the absorption of the acidic side products13a and an
unusual reaction selectivity13b. In this paper, we report a
visible-light-promoted reaction with water as co-solvent for
the synthesis of versatile carbazoles from 2-azidobiphenyls
with high yield, good tolerance of functional groups, wide
Azides as amino group sources in C−H amination have
unique advantages,6 such as ease of preparation, performance
under non-oxidative and non-basic conditions, and generation
o
f
N
2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 6
View Article Online
DOI: 10.1039/C7GC03392C
ARTICLE
Journal Name
Entry
1
2
3
4
Solvent
Toluene
CCl4
MeOH
MeCN
Time(h)
Yield [%]b
28
applications and N2 as essentially the only by-product (Scheme
1B).14,15
18
18
18
18
18
18
18
36
36
36
36
36
36
36
36
36
36
44
49
40
Results and discussion
5
6
7
THF
DMF
H2O
H2O
60
42
We began our investigation by screening the substrate, 2-
azidobiphenyl in the presence of a fluorescent lamp as a
source of visible light (Table 1).8i The initial results were
45(54)
60(39)
45(54)
75(24)
64(35)
58(40)
78(21)
80f(19)
67(22)
75(23)
<5
8
9c
H2O
10d
11e
12e
13e
14e
15e
16e
17g
H2O/Acetone = 1/1
H2O/MeOH = 1/1
H2O/DCM = 1/1
H2O/CH3CN = 1/1
H2O/Acetone = 1/1
H2O/Acetone = 10/1
H2O/Acetone = 1/10
H2O/Acetone = 1/1
unsatisfactory, because either the low yield or the side
8,9
products were produced
under different organic solvents
(entries 1-6). A clean reaction was achieved in the presence of
water as the solvent (entry 7). Water has not been used
previously in the photodecomposition reactions of azides.
Under these conditions, carbazole (2a) is obtained from 1a in
4
5
%
y
i
e
l
d
.
Visible light: Fluorescent lamp 23 W, 28 oC to 32 oC,. Yield of 2a was
determined by 1H- NMR, recovered yield of 1a was determined by 1H NMR and is
shown in brackets. c Fluorescent lamp 18 W. Solvent (1.5 mL/1.5 mL). Solvent
(1.5 mL/1.5 mL), silica gel 15 mg. f Isolated yield of 2a by column chromatography.
g Without irradiation.
a
b
d
e
Table 2. Scope of 2-Azidobiphenyla
Fluorescent lamp 23 W
R
R'
R'
R
N2
+
N
H
2b-z
N3
1b-z
H2O/Acetone (1/1), 48 h
Me
NC
Ph
MeO
N
N
N
N
Scheme 1. Synthetic methods for carbazoles from 2-azidobiphenyls
H
H
H
H
2b, 95% (85%b)
2c, 97% (77%b)
2d, 83%c
2e, 90%c
Analysis based on 1H NMR revealed that 54% of starting
material (1a) was left unchanged. However prolongation of the
reaction time or changes in the power of the irradiation failed
to improve the yield (entries 8-9) possibly because of the poor
solubility of 1a in water. Screening a variety of water co-
OHC
MeHNOC
MeOC
EtO2C
N
N
N
N
H
H
H
H
2i, 88% (68%b)
2g, 83%
2h, 94% (90%b)
2f, 92%
Cl
I
F
Br
solvents (entries 10-13), revealed that
a water/acetone
mixture, assisted by of silica gel16 gives yields as high as 80%
(entries 14-16). Under these conditions, side-products such as
diazo or ring-opened products which are usually unavoidable
in photochemistry,8 were not found. 2a was not observed
without visible light irradiation (entry 17).
N
N
N
N
H
H
H
H
2j,91% (66%b)
2k, 92% (75%b)
2l,95% (81%b)
2m,
b
86% (85% )
MeO
Ph
F
OMe
N
N
N
H
H
H
N
With the optimized reaction conditions, we next explored
the scope and generality of this method (Table 2).17 Various
substrates with a substituent in the azidophenyl ring were
examined. Substrates containing either electron-donating
H
2o, 97% (62%b)
2p, 90 (70%b)
2n, 80%
2q, 94%
OMe
Me
N
N
OMe
N
Me
N
H
H
groups (EDG) (2b
-d) or electron-withdrawing groups (EWG)
2r
2r'
H
2s
2b
H
2r + 2r', 89% (1:1)c
2s + 2b, 81% (1.5:1)c
(
2e-i) in the azidophenyl ring reacted smoothly under the
MeO
s
t
a
n
d
a
r
d
Me
Table 1. Optimization of Reaction Conditions. a
CO2Et
CHO
N
N
N
H
N
H
H
MeO
Me
H
2w, 89% (74%b)
2v, 89% (56%b)
2t, 87%
2u, 90%
Me
O
HN
2y, 93%
N
HN
H
Ph
OMe
OMe
2z, 80%c
2x, 93%
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 3 of 6
View Article Online
DOI: 10.1039/C7GC03392C
Journal Name
ARTICLE
a Standard conditions unless otherwise noted: 0.15 mmol 1, fluorescent lamp 23
intermolecular competitive reaction, there is
a slight
W, H2O / Acetone (1.5mL/1.5 mL), silica gel 15 mg, 28 oC to 32 oC, 48 h, isolated
difference between EDG (1b) and EWG (1g) substituents in the
b
yield based on 100% conversion or the conversion shown in brackets.
azidophenyl ring (Scheme 3a). When the competing reaction
Conversion. c 4 days.
between the substrate with EWG (1p) and that with EDG (1u
)
in the phenyl ring is performed, the compound with EWG in
the phenyl ring predominates (Scheme 3b), indicating that the
reaction may not proceed through electrophilic C−H
amination. We analyzed potential kinetic isotope effects by
examining the reaction of monodeuterated aryl azide (1a-D)
(Scheme 3c). No isotope effect was observed in this reaction
which is same as that in the non-catalytic thermal reaction7,
indicating the visible-light-promoted process may have a
similar rate-determining step, namely extrusion of N2.18 In the
conditions, giving desired carbazoles in high yields. Functional
groups commonly used in organic synthesis, such as ester,
cyano, carbonyl and aldehyde as well as acylamino groups are
tolerated. For the substrate 2-azido-5-nitro-1,1'-biphenyl, less
than 5% conversion was observed. The reaction of 2-
azidobiphenyl bearing halogen atoms in the azidophenyl ring
provides the corresponding halogenated carbazoles (2j-m) in
good to excellent yields, and this provides more options for
further conversions of products. Next, substrates with
substituents in the unsubstituted phenyl ring of 2-
intramolecular competing reaction of the aromatic azide 1aa
,
which has a phenyl group with both EWG and EDG
azidobiphenyl (2n-w) were examined. The phenyl rings
substituents in the ortho position, two isomers were formed in
equal amounts. This result suggests again that the extrusion of
N2 is the rate-determining step.
substituted with EDG groups such as methyl, methoxyl and
EWG groups such as ester and aldehyde are tolerated. When
there is a substituent in the m-position of this phenyl ring, a
Based on the above results and earlier research on photo-
decomposition of azides,8,10,18 we propose the following
mixture of products (2r/r′, 2s/b) is obtained in good yield but
w i t h l o w r e g i o s e l e c t i v i t y . T h e s e
mechanism (Scheme 3). The azide (
1) is transformed to a
n
i
t
r
e
n
e
Scheme 3. Proposed mechanism
R2
R1
R2
a) Pd(OAc)2 (2 mol %)
Br
c) standard
conditions
2R-PhB(OH)2 (3.0 equiv )
R1
R1
N
N3
NH2 b) NaNO2, NaN3
H
4
3
MeO
Me
MeO2C
4a, 94% (85%b)
Glycoborine
4b, 94%c
Clausine C
OMe
N
N
H
H
MeO2C
MeO2C
MeO
c
c
4c
, 88%
4d
, 87%
OMe
MeO
Clausine L
Clausine H
N
N
H
H
OHC
c) standard
conditions
HOH2C
PMP
OHC
PMP
d) IBX
OMe
N3
N3
N
H
Scheme 2. Competitive Experiments
PMP = p-methoxylphenyl
b
4e
, 94% (80% )
Clauszoline-K
3e'
3e
observations are consistent with previous reports on metal-
catalyzed processes.10b In particular, sterically hindered
substrates can be successfully converted to target products
HO2C
MeO2C
ref. 18a
ref. 18a
OMe
4b
OH
N
N
H
(
2x-y). 1-Heteroaryl-2-azidoarenes are tolerated under the
H
Clausine N
Clausine M
reaction condititions, producing 2z and showing that this
method has potential application to the synthesis of
heteroarene fused carbazoles, such as furostifoline (Figure 1).
However, few desired product was observed when 3-azido-4-
phenylpyridine was used as substrate.
a Isolated yield based on based on 100% conversion or the conversion shown in brackets.
b Conversion. c Time 4 days.
Scheme 4. Synthesis of carbazole alkaloidsa
intermediate (
intermediate (
A
) by release of N2 under visible light. Then the
In order to study the mechanism of the reaction, we first
performed several competition experiments (Scheme 2). In the
B
) is formed rapidly by electrocyclic ring closure.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 6
View Article Online
DOI: 10.1039/C7GC03392C
ARTICLE
Journal Name
Through a [1, 5] H-shift,
B
is transformed to the final product
Substrate
1
(0.15 mmol), silica gel 15.0 mg, H2O (1.5 mL) and
(
2)by tautomerization.
acetone (1.5 mL) were added to a 15 mL glass vial equipped
Inspired by the good functional group tolerance of this with a stirring bar. The solution was stirred for 48 h at a
reaction, we attempted to synthesize a series of bioactive distance of ~1 cm from a 23 w fluorescent lamp. Then, the
natural carbazoles. As shown in Scheme 4, 2-aminobiaryls, solution was diluted with 5 mL of water and 5 mL of CH2Cl2 and
ideal precursors of 2-azidobiaryls were synthesized from the the phases were separated. The aqueous phase was extracted
commercially available substituted 2-bromoanilines and with an additional of CH2Cl2 (3 × 5 mL), and the combined
substituted phenylboronic acid using Suzuki reactions (step a, organic phases were washed with water (2 × 5 mL). The
see Supporting Information).19 Without purification, the organic phase was dried over Na2SO4, then filtered and
resulting 2-aminobiaryls were converted to 2-azidobiphenyls in concentrated. The crude product was purified by flash
moderate to good yields using traditional diazotization chromatography on silica gel to give the desired product
reaction conditions (step b, see Supporting Information). Using
2.
our standard conditions, the obtained 2-azidobiphenyls were
Acknowledgements
converted to carbazoles smoothly (step c). Based on this
simple and general synthetic procedure, various natural
alkaloids were obtained in high yields,20 including the anti-HIV
We would like to acknowledge financial support from the
National Natural Science Foundation of China (No. 21332005,
21472085), the Fundamental Research Funds for the Central
Universities (No. 020514380114).
drug glycoborine (4a),21 clausine C
(
clauszoline-L) (4b),22
clausine L(4c),23 clausine H (4d
and clauszoline K (4e). It
24
)
should be noted that these compounds could be easily
converted to other nature alkaloids. For example, clausine C
can be easily converted into clausines M and N by known
methods.20a
Conflicts of interest
There are no conflicts to declare.
In order to investigate the potential applications in
biochemistry of this reaction, several experiments were
Notes and references
1
(a) H.-J. Knölker and K. R. Reddy, Chem. Rev. 2002, 102,
4303; (b) H.-J. Knoelker, Top. Curr. Chem. 2005, 244, 115; (c)
A. W. Schmidt, K. R. Reddy and H. J. Knölker, Chem. Rev.
2012, 43, 3193; (d) W. Maneerat, T. Ritthiwigrom, S.
Cheenpracha, T. Promgool, K. Yossathera, S. Deachathai, W.
Phakhodee and S. Laphookhieo, J. Nat. Prod. 2012, 75, 741.
For selected examples: (a) A. A. Mousawi, F. Dumur, P.
Garra, J. Toufaily, T. Hamieh, B. Graff, D. Gigmes, J. P.
Fouassier and J. Lalevée, Macromolecules 2017, 50, 2747; (b)
L. Zhu, Y. Shan, R. Wang, D. Liu, C. Zhong, Q. Song, F. Wu,
Chem. - Eur. J. 2017, 23, 4373; (c) Y. Gawale, N. Adarsh, S. K.
Kalva, J. Joseph, M. Pramanik, D. Ramaiah and N. Sekar,
Chem. - Eur. J. 2017, 23, 6570; (d) A. Al Mousawi, D. M. Lara,
G. Noirbent, F. Dumur, J. Toufaily, T. Hamieh, T.-T. Bui, F.
Goubard, B. Graff, D. Gigmes, J. P. Fouassier and J. Lalevée,
Macromolecules 2017, 50, 4913.
2
Scheme 5. Large scale reaction or the reaction performed in acidic or alkaline
buffer solutions
performed. As can be seen in Scheme 5, this has little influence
on yield and no decomposition products were observed either
in acidic buffer solution or in alkaline buffer solution. When
the large scale reaction was performed, the desired product 2a
was still achieved in a reasonable yield (69%). It was noted that
2a and 1a could be separated by washing with n-hexane (see
the details in ESI).
3
4
5
I. Bauer and H.-J. Knoelker, Top. Curr. Chem. 2012, 309, 203.
N. Yoshikai and Y. Wei, Asian J. Org. Chem. 2013, 2, 466.
For selected reviews: (a) X.-X. Guo, D.-W. Gu, Z. Wu and W.
Zhang, Chem. Rev. 2015, 115, 1622; (b) J. Jiao, K. Murakami
and K. Itami, ACS Catal. 2016, 6, 610; (c) Y. Park, Y. Kim and
S. Chang, Chem. Rev. 2017, 117, 9247. For selected examples
of the synthesis of N-substituted carbazoles, see: (d) W. C. P.
Tsang, N. Zheng and S. L. Buchwald, J. Am. Chem. Soc. 2005,
127, 14560; (e) J. A. Jordan-Hore, C. C. C. Johansson, M.
Gulias, E. M. Beck and M. J. Gaunt, J. Am. Chem. Soc. 2008,
130, 16184; (f) S. H. Cho, J. Yoon, S. Chang, J. Am. Chem. Soc.
2011, 133, 5996; (g) A. P. Antonchick, R. Samanta, K. Kulikov
and J. Lategahn, Angew. Chem., Int. Ed. 2011, 50, 8605; (h) S.
W. Youn, J. H. Bihn and B. S. Kim, Org. Lett. 2011, 13, 3738;
For Selected examples of the synthesis of N-H carbazoles,
see: (i) Q. Jiang, D. Duan-Mu, W. Zhong, H. Chen and H. Yan,
Chem. - Eur. J. 2013, 19, 1903; (j) K. Takamatsu, K. Hirano, T.
Satoh and M. Miura, Org. Lett. 2014, 16, 2892; (k) C. Suzuki,
K. Hirano, T. Satoh and M. Miura, Org. Lett. 2015, 17, 1597;
(l) S. Choi, T. Chatterjee, W. J. Choi, Y. You and E. J. Cho, ACS
Conclusions
In summary, we have developed a light-promoted and
metal-free intramolecular (Sp2)-H amination of readily
available 2-azidobiphenyls. This transformation is practical and
has wide application as demonstrated by the preparation of
various bioactive carbazole alkaloids. We anticipate the
method, with its mild conditions, clean reactions,
environmentally friendly and exceptional atom economy may
have extensive application in biochemistry and synthetic
chemistry.
Experimental
Catal. 2015,
5
, 4796.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 5 of 6
View Article Online
DOI: 10.1039/C7GC03392C
Journal Name
ARTICLE
6
(a) S. Bräse, C. Gil, K. Knepper and V. Zimmermann, Angew. 16 (a) H. B. Lee, M. J. Sung, S. C. Blackstock and J. K. Cha, J. Am.
Chem., Int. Ed. 2005, 44, 5188; (b) H. Lu and X. P. Zhang, Chem. Soc. 2001, 123, 11322; (b) S. Maity and N. Zheng,
Chem. Soc. Rev. 2011, 40, 1899; (c) C. M. Che, V. K. Y. Lo, C. Angew. Chem., Int. Ed. 2012, 51, 9562.
Y. Zhou and J. S. Huang, Chem. Soc. Rev. 2011, 40, 1950; (d) 17 (a) H. J. Knölker, M. Bauermeister and J. B. Pannek, Chem.
D. Intrieri, P. Zardi, A. Caselli and E. Gallo, Chem. Commun.
2014, 50, 11440; (e) K. Shin, H. Kim and S. Chang, Acc. Chem.
Res. 2015, 48, 1040.
Ber. 1992, 125, 2783; (b) T. Watanabe, S. Oishi, N. Fujii and
H. Ohno, J. Org. Chem. 2009, 74, 4720; (c) D.-Y. Goo and S.
K. Woo, Org. Biomol. Chem. 2016, 14, 122.
7
8
(a) M. Pudlo, D. Csanyi, F. Moreau, G. Hajos, Z. Riedl and J. 18 (a) B. J. Stokes, H. Dong, B. E. Leslie, A. L. Pumphrey andT. G.
Sapi, Tetrahedron 2007, 63, 10320; (b) E. Ullah, J. Mcnulty
and A. Robertson, Eur. J. Org. Chem. 2012, 2127; (c) Y. Ou
and N. Jiao, Chem. Commun. 2013, 49, 3473.
Driver, J. Am. Chem. Soc. 2007, 129, 7500; (b) J. G. Harrison,
O. Gutierrez, N. Jana, T. G. Driver and D. J. Tantillo, J. Am.
Chem. Soc. 2016, 138, 487.
(a) J. S. Swenton, T. J. Ikeler and B. H. Williams, J. Am. Chem. 19 L. Liu, Y. Zhang and Y. Wang, J. Org. Chem. 2005, 70, 6122.
Soc. 1970, 92, 3013; (b) P. A. Lehman and R. S. Berry, J. Am. 20 (a) M. P. Krahl, A. Jager, T. Krause and H.-J. Knölker Org.
Chem. Soc. 1973, 95, 8614; (c) R. J. Sundberg and R. W.
Heintzelman, J. Org. Chem. 1974, 39, 2546; (d) R. J.
Sundberg, D. W. Gillespie and B. A. DeGraff, J. Am. Chem.
Soc. 1975, 97, 6193; (e) N. P. Gritsan and E. A. Pritchina,
Russ. Chem. Rev. 1992, 61, 500; (f) N. P. Gritsan, T. Yuzawa
Biomol. Chem., 2006,
‐
Schmidt and H. J. Knölker, Eur. J. Org. Chem. 2014, 4741; (c)
D. Ma, J. Dai, Y. Qiu, C. Fu and S. Ma, Org. Chem. Front.,
2014, 1, 782.
4, 3215; (b) C. Schuster, C. Börger, K. K.
Julich Gruner, R. Hesse, A. Jäger, G. Kaufmann, A. W.
and M. S. Platz, J. Am. Chem. Soc. 1997, 119, 5059; (g) R. 21 (a) Bautista, R.; P. Montoya, A.; Rebollar, A.; Burgueño, E.
Born, C. Burda, P. Senn and J. Wirz, J. Am. Chem. Soc. 1997,
119, 5061; (h) W. T. Borden, N. P. Gritsan, C. M. Hadad, W. L.
Karney, C. R. Kemnitz and M. S. Platz, Acc. Chem. Res. 2000,
and Tamariz, J. Molecules 2013, 18, 10334; (b) C. Brütting, R.
Hesse, A. Jäger, O. Kataeva, A. W. Schmidt and H.-J. Knölker,
Chem. Eur. J. 2016, 22, 16897.
33, 765; UV−vis spectra of 2-azidobiphenyl was reported in 22 (a) H.-J. Knölker and M. Wolpert, Tetrahedron, 2003, 59
(i) T. S. Chung, A. J. L. Ayitou, J. H. Park, V. M. Breslin and M. 5317; (b) R. Forke, M. Krahl, F. Däbritz, A. Jäger and H. J.
A. Garcia-Garibay, J. Phys. Chem. Lett., 2017, , 1845. Knölker, Synlett, 2008,1870; (c) R. Forke, A. Jager and H.-J.
Knolker, Org. Biomol. Chem. 2008, , 2481. (d) Kuethea, J. T.
and Childers, K. G. Adv. Synth. Catal. 2008, 350, 1577.
,
8
9
(a) M. L. Tsao, N. Gritsan, T. R. James, M. S. Platz, D. A.
Hrovat and W. T. Borden, J. Am. Chem. Soc. 2003, 125, 9343;
6
(b) E. Bremusköbberling, A. Gillner, F. Avemaria, C. Réthoré 23 Rasheed, S.; Rao, D. N.; Reddy, K. R.; Aravinda, S. and
and S. Bräse, Beilstein J. Org. Chem. 2012, , 1213. Vishwakarma, R. A. RSC Adv. 2014, , 4960.
10 (a) B. J. Stokes, B. Jovanović, H. Dong, K. J. Richert, R. D. Riell 24 (a) Kataeva, O.; Krahl, M. P. and Knolker, H.-J. Org. Biomol.
and T. G. Driver, J. Org. Chem. 2009, 74, 3225; (b) B. J. Chem., 2005, , 3099; (b) M. P. Krahl, O. Kataeva, A. W.
Stokes, K. J. Richert and T. G. Driver, J. Org. Chem. 2009, 74 Schmidt and H.-J. Knölker, Eur. J. Org. Chem., 2013, , 59.
8
4
3
,
1
6442; (c) W. G. Shou, J. Li, T. Guo, Z. Lin and G. Jia,
Organometallics 2009, 28, 6847; (d) A. L. Pumphrey, H. Dong
and T. G. Driver, Angew. Chem., Int. Ed. 2012, 51, 5920; (e)
Q. Zhang, C. Wu, L. Zhou and J. Li, Organometallics 2013, 32
415; (f) L. Chen, T. Yang, H. Cui, T. Cai, L. Zhang and C.-Y. Su,
J. Mater. Chem. A 2015, , 20201; (g) I. T. Alt and B. Plietker,
,
3
Angew. Chem., Int. Ed. 2016, 55, 1519; (h) L. Yang, H. Li, H.
Zhang and H. Lu, Eur. J. Org. Chem. 2016, 34, 5611.
11 Boron promoted decomposition of 2-azidobiphenyls: (a) P.
Zanirato, J. Organomet. Chem. 1985, 293, 285; (b) P.
Spagnolo and P. Zanirato, J. Chem. Soc. Perkin Trans 1, 1988,
2615. Aluminium promoted decomposition of 2-
azidobiphenyls: (c) H. Takeuchi, M. Maeda, M. Mitani, K.
Koyama, J. Chem. Soc., Perkin Transactions 1, 1987, 57.
12 (a) H. Lu, C. Li, H. Jiang, C. L. Lizardi and X. P. Zhang, Angew.
Chem., Int. Ed. 2014, 53, 7028; (b) H. Lu, K. Lang, H. Jiang, L.
Wojtas and X. P. Zhang, Chem. Sci. 2016, 7, 6934; (c) T.
Zhang, Z. Wang, X. Hu, M. Yu, T. Deng, G. Li and H. Lu, J. Org.
Chem. 2016, 81, 4898; (d) T. Zhang, X. Hu, Z. Wang, T. Yang,
H. Sun, G. Li and H. Lu, Chem. - Eur. J. 2016, 22, 2920.
13 (a) M. A. Ali, X. Yao, H. Sun and H. Lu, Org. Lett. 2015, 17
,
1513; (b) M. A. Ali, X. Yao, G. Li and H. Lu, Org. Lett. 2016, 18
1386.
,
14 For recent visible-light-induced synthesis of carbazoles, see:
(a) A. C. Hernandezperez and S. K. Collins, Angew. Chem., Int.
Ed. 2013, 52, 12696; (b) Z.-G. Yuan, Q. Wang, A. Zheng, K.
Zhang, L.-Q. Lu, Z. Tang and W.-J. Xiao, Chem. Commun.
2016, 52, 5128; (c) T. Chatterjee, G.-b. Roh, M. A. Shoaib, C.-
H. Suhl, J. S. Kim, C.-G. Cho and E. J. Cho, Org. Lett. 2017, 19
1906;
,
15 Sustainable and environmentally friendly technologies for
molecular synthesis, see: (a) A. Albini and M. Fagnoni, Green
Chem., 2004,
Oelgemöller, Green Chem., 1999,
6
, 1; (b) A. G. Griesbeck, W. Kramer and M.
1
, 205.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Green Chemistry
Page 6 of 6
View Article Online
DOI: 10.1039/C7GC03392C
Visible light rather than various metals is reported to promote the synthesis of various
carbazoles from readily available 2-azidobiphenyls under mild conditions.