Photoinduced C-H direct arylation of unactivated arenes

Article abstract of DOI:10.1007/s11426-015-5377-y

Two general protocols have been developed for the photoinduced, metal-free direct arylation of unactivated arenes with aryl iodide. Both methods gave good to excellent yields for most substrates. Notably, the C-F bond in method A and the C-F, C-Cl, and C-Br bonds in method B could survive the arylation reaction. These methods offered excellent options for syntheses of biaryls.

Full text of DOI:10.1007/s11426-015-5377-y

SCIENCE CHINA
Chemistry
• ARTICLES •
doi: 10.1007/s11426-015-5377-y
· SPECIAL ISSUE · CH bond activation
Photoinduced C–H direct arylation of unactivated arenes
Jian Kan, Shijun Huang, Huaiqing Zhao, Jin Lin & Weiping Su*
State Key Laboratory of Structural Chemistry; Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, China
Received December 10, 2014; accepted December 29, 2014
Two general protocols have been developed for the photoinduced, metal-free direct arylation of unactivated arenes with aryl
iodide. Both methods gave good to excellent yields for most substrates. Notably, the C–F bond in method A and the C–F, C–Cl,
and C–Br bonds in method B could survive the arylation reaction. These methods offered excellent options for syntheses of
biaryls.
C–H bond activation, photoinduced, free radical, aryl iodide
diamine was reported [6]. After initial reports of the transi-
1 Introduction
tion metal-free direct arylation of unactivated aromatic C–H
bonds, other organic small molecules were found to cata-
lyze such a cross-coupling reaction [7]. This type of base-
mediated arylation was likely to undergo a radical pathway.
Organomolecules may interact with the tert-butoxide
(KOtBu or NaOtBu) to initiate the aryl radicals via single-
electron transfer (SET). These newly developed strategies
have many significant advantages over the traditional cross-
coupling methods in some respects [4d].
Visible-light photoredox catalysis, which usually uses
metal-organic complex (Ru or Ir compounds) or organic
dyes as photoinitiators to undergo SET processes with or-
ganic substrates under visible light irradiation, has been
successfully developed and applied to organic synthesis in
recent years [8]. A household compact fluorescent light bulb
(CFL) was usually used as the light source. The limited ex-
ploration of this area has already seen many significant and
exciting results [9]. However, only a few substances such as
aryldiazonium and diaryliodonium salts have been explored
in this kind of arylation reaction [10]. Photoinduced biaryl
formation between aryl halides and unactivated arenes un-
der UV irradiation has been studied for many years [11].
Aryl halides can be used as radical precursors. At the very
beginning, we envisioned that this kind of biaryl could be
The biaryl motif, one of the most important structural units,
is widely found in medicinal compounds and functional
materials [1]. The cross-coupling reactions catalyzed by
late-transition metals, including C–H functionalization, are
the most powerful tools in the construction of biaryl deriva-
tives [1e,2]. However, these strategies suffer from many
limitations, including using expensive transition-metal cat-
alysts, toxic ligands, harmful oxidants, and other organic
additives [3]. The recent breakthrough was the use of or-
gancatalysts for cross-coupling construction of biary com-
pounds in which some organomolecules can efficiently cat-
alyze direct cross-coupling of unactivated aromatic C–H
bonds with aryl halides [4].
In 2008, Itami and coworkers [5] reported for the first
time that the cross-coupling between electron-deficient ni-
trogen heterocycles and haloarenes can be efficiently pro-
moted by potassium t-butoxide alone under microwave irra-
diation. Recently, the strong base-mediated coupling reac-
tion of arylhalides with benzene derivatives using catalytic
1,10-phenanthroline derivatives or N,N′-dimethyl-ethylene
*Corresponding author (email: wpsu@fjirsm.ac.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2015
chem.scichina.com link.springer.com

2
Kan et al. Sci China Chem July (2015) Vol.58 No.7
achieved through visible a light-driven SET process in the
presence of a photosensitizing reagent. Recently, a similar
result was achieved by Li et al. [12] using Ir(ppy)3 as the
sensitizing agent. Interestingly, after repeated attempts, we
found that the cross-coupling reaction of aryl halide with
unactivated benzenes could effectively offer biaryls in the
presence of KtOBu whether or not the photosensitizer was
present under the irradiation of a household CFL (Scheme 1).
mmol), bathophenanthroline (8.3 mg, 0.025 mmol), KOtBu
(56 mg, 0.5 mmol), and benzene (2.0 mL) was added by
syringe. Then the Schlenk tube was sealed by a Teflon
screwcap and placed with one 24 W CFL (approximately
3 cm away). The reaction mixture was allowed to stir for
36 h. Then the solvent was removed in vacuo and the resi-
due was purified by chromatography on silica gel (eluent:
diethyl ether/petroleum ether) to provide the corresponding
product.
All products are known compounds and the data are
1
agreement with the literature data. The H NMR and 13C
2 Experimental
NMR data and spectra can be seen in the Supporting Infor-
mation online.
2.1 General information
All reactions were carried out under dry N2 with dry sol-
vents under anhydrous conditions. Aryl iodides were used
without further purification. Benzene was distilled from
sodium under nitrogen and stored under nitrogen. KOtBu
was sublimed before being used. GE 24 W compact fluo-
rescent light bulbs (FLE24HLX/865/Edison Plus/Day
3 Results and discussion
To optimize the reaction conditions, we initially studied the
cross-coupling reaction between 4-iodoanisole (1a) and
benzene (2a) as a model with 24 W household CFL as the
light source. When the reaction was carried out at room
temperature, less than 8% of the desired coupling product
3a was formed (Table 1, Entry 1). The reaction rate was
dramatically increased when the temperature was raised
(Entries 2 and 3). When the reaction was carried out at
1
Light/6500 K) were used as the light source. H NMR (400
MHz) and 13C NMR (100 MHz) spectra were obtained on a
Bruker Avance III 400 spectrometer (Switzerland) with
CDCl3 as solvent and tetramethylsilane (TMS) as internal
standard. Chemical shifts were reported in units (ppm) by
1
assigning TMS resonance in the H NMR spectra as 0.00
ppm (chloroform, 7.26 ppm). Gas chromatography (GC)
and gas chromatography-mass spectra (GC-MS) were per-
formed by the analysis center of our institute. The GC
yields were obtained after amendment by standard curve,
with dodecane as the internal standard.
Table 1 Selected screening results for reacion conditions a)
Entry
1
Catalyst
Base
Solvent
Yield (%) b)
<8
T (°C)
–
–
–
–
–
–
–
–
–
–
–
–
KOtBu
KOtBu
KOtBu
KOtBu
LiOtBu
NaOtBu
NaOMe
K2CO3
–
–
–
–
–
–
–
–
r.t.
90
2.2 General experimental procedures and characteri-
zations
2
69
3
4 c)
100
100
100
100
100
100
100
100
100
100
r.t.
93
<5 c)
Method A: in a glove box, a 25 mL Schlenk tube equipped
with a stir bar was charged with aryl iodides (0.25 mmol),
KOtBu (56 mg, 0.5 mmol), and benzene (2.0 mL) was add-
ed by syringe. Then the Schlenk tube was sealed by a Teflon
screwcap and placed in an oil bath at 100 °C (preheated to
100 °C) with one 24 W CFL (approximately 5 cm away).
The reaction mixture was allowed to stir for 16 h. After be-
ing cooled down, the solvent was removed in vacuo and the
residue was purified by chromatography on silica gel (elu-
ent: diethyl ether/petroleum ether) to provide the corre-
sponding product.
5
NR
6
NR
7
NR
8
NR
9
K2CO3 DMSO (0.5 mL)
K2CO3 MeCN (0.5 mL)
NaOtBu DMSO (0.5 mL)
trace
trace
54
10
11
12 d)
13
14
15
16
17
KOtBu
–
–
–
–
–
–
NR
L1 (0.1) e) KOtBu
L1 (0.1)
KOtBu
L2 (0.1) e) KOtBu
36
42 f)
Method B: in a glove box, a 25 mL Schlenk tube
equipped with a stir bar was charged with aryl iodides (0.25
r.t.
r.t.
60
L2 (0.1)
L2 (0.1)
KOtBu
KOtBu
r.t.
97 f)
8 c)
r.t.
a) Reaction conditions: 1a (0.25 mmol), 2a (2mL), base (2 equiv.), 16 h,
N2; b) GC yield; c) the reaction was carried out in dark; d) the reaction was
carried out in air; e) L1=1,10-phenanthroline, L2=4,7-diphenyl-1,10-phen-
anthroline; f) reaction time: 36 h.
Scheme 1 Photoinduced C–H direct arylation of unactivated arenes.

Kan et al. Sci China Chem July (2015) Vol.58 No.7
3
Table 2 Direct arylation reactions of aryl iodides with benzene
100 °C, the yield increased up to 93% (Entry 3). In sharp
contrast, the yield dropped to less than 5% when the reac-
tion was performed without light, indicating that light has a
significant impact on the reaction (Entry 4). Other bases
such as LiOtBu, NaOtBu, NaOMe, and K2CO3 were also
tested. However, none of them gave arylated product (En-
tries 5–8). DMSO or MeCN was added as the cosolvent to
improve the solubility of K2CO3 (Entries 9–11), but no
product was formed. When NaOtBu was used in the pres-
ence of 0.5 mL DMSO, the reaction furnished product 3a in
54% yield (Entry 11).
More interestingly, when 1,10-phenanthroline or 4,7-
diphenyl-1,10-phenanthroline was used as the catalyst (En-
tries 13–16), light was able to drive this direct arylation at
room temperature. 4-Methoxybiphenyl was formed in a
significantly higher yield with 4,7-diphenyl-1,10-phenan-
throline as catalyst than with 1,10-phenanthroline. These
optimization studies led to the discovery of two general
methods: (1) method A, which runs reaction at 100 °C un-
der irradiation by light from household CFLs without cata-
lyst (Entry 3); (2) method B, which elicited reaction at room
temperature under irradiation by light from household CFLs
with a photosensitizer catalyst (Entry 16). Both methods
gave excellent yields in the coupling reaction of 4-iodoa-
nisole (1a) with benzene (2a).
With two optimized reaction conditions in hand, we ex-
amined the scope of the reaction. A variety of aryl iodides
were initially investigated using method A. Among these
aryl iodides, substrates with electron-donating groups (Ta-
ble 2, Entries 1–5, 16–18) and electron-withdrawing groups
(Entries 8,9) all worked well under the standard conditions.
For methoxy groups on the phenyl rings of aryl iodides, the
ortho-substituted and the para-substituted ones gave slight-
ly higher yields than the meta-substituted one (Entries 1–3).
Steric effect had some impact on the reaction. For example,
4-iodotoluene and 3-iodotoluene gave the corresponding
biphenyl product in 78% and 60% isolated yields, whereas
2-iodotoluene only gave 20% yield (Entry 6). Simple iodo-
benzene and 1-iodonaphthalene can be efficiently coupled
with benzene to produce the desired products in high yields
(Entries 7, 10). 4-Fluoro-1-iodobenzene afforded the
4-fluorobiphenyl in 69% yield (Entry 13). 4-Chloro-1-
iodobenzene and 4-bromo-1-iodobenzene were also tested;
both gave good yields of the terphenyl product (Entries 14,
15). 2-Phenylpyridine and 3-phenylpyridine could be iso-
lated in good yield when 2-iodo or 3-iodopyridine was used
as substrate (Entries 11, 12).
a) Method A condition: 4-iodoanisole (0.25 mmol), KOtBu (2 equiv.)
and benzene (2 mL) in a sealed Schlenk tube, 100 °C, 16 h, isolated yields;
b) method B condition: 4-iodoanisole (0.25 mmol), KOtBu (2 equiv.),
4,7-diphenyl-1,10-phenanthroline (10 mol%) and benzene (2 mL) in a
sealed Schlenk tube, r.t., 36 h, isolated yields; c) 45 W CFL; d) 14%
p-terphenyl was isolated.
Six aryl iodides bearing different substituents were se-
lected for further investigation using method B. The reac-
tions were carried out under mild reaction conditions. All
furnished the corresponding biaryls in excellent yields (Ta-
ble 2, Entries 1, 7–8, 13–15). More interestingly, when
4-chloro-1-iodobenzene and 4-bromo-1-iodobenzene were
checked with method B, the respective isolated products
were 4-chlorobiphenyl and 4-bromobiphenyl and the chloride
and bromide substituents were untouched (Entries 14, 15).
This result is completely different than the results of method
A as well as previous reports [6c,7b,7h]. In most if those

4
Kan et al. Sci China Chem July (2015) Vol.58 No.7
cases, terphenyl was the main product when 4-chloro-1-
iodobenzene or 4-bromo-1-iodobenzene was used as sub-
strate. In a few cases, 4-chlorobiphenyl was isolated in high
yields. The compatibility of C–Cl and C–Br bonds with the
reaction conditions offers a great opportunity to further
functionalize the products.
Other arenes were also explored under the standard con-
ditions. With increased electron density inarenes such as
toluene and anisole, low efficiency was observed, while
electron-deficient arenes such as pyrazine, benzonitrile and
pyridine all gave excellent yields (Table 3, Entries 1, 2, 4,
5). The direct arylation of asymmetric arenes with 1a af-
forded the corresponding products as a mixture of regioi-
somers (Entries 2–6) with the ortho-arylated and meta-
arylated products being the major isomers.
Scheme 2 Kinetic isotope effect of light-driven direct arylation reaction
by method A and method B.
In order to understand the mechanism of this light-driven
direct arylation reaction, several experiments were per-
formed. Addition of one equivalent of TEMPO, a free-
radical scavenger, completely shut down the reactions under
both method A and method B conditions. Two kinetic iso-
tope experiments using a mixture of benzene and D6-benzene
with 1a were conducted. The observed kinetic isotopic ef-
fects were KH/KD=1.2 for method A and KH/KD=1.16 for
method B. Both values were low, which demonstrated that
the C–H bond cleavage of benzene was not the rate-limiting
step in these reactions (Scheme 2).
Because most of the aryl iodides used in this work only
absorb UV radiation, the household CFL lamp may contain
wavelengths in the ultraviolet region of the spectrum that
actually initiated the reaction. On the basis of the above data
and related results published previously [4,11b,13], the re-
actions are proposed to proceed a free-radical mechanism as
shown in Scheme 3. Under irradiation by CFL, the excited
triplet state of aryl iodide 1a undergwent electron transfer
with KOtBu or KOtBu coordinated complex to afford aryl
Scheme 3 The proposed mechanism of light-driven direct arylation reaction.
radical I, which was subsequently added to benzene to gen-
erate the cyclohexadienyl radical intermediate II. Then the
intermediate was oxidated and deprotonated by t-BuO radi-
cal to produce the desired product 3. When 4,7-diphenyl-
1,10-phenanthroline was added as the catalyst, the organo-
molecule efficiently promoted the SET and deprotonation
process and the arylation reaction occurred more easily.
4 Conclusions
We have disclosed a novel photoinduced direct arylation of
unactivated arenes with aryl iodide. Two methods have
been successfully developed. Both methods gave good to
excellent yields for most substrates. Notably, the C–F bond
for method A and the C–F, C–Cl, and C–Br bonds for
method B survived during the arylation reaction. This new
methodology presumably proceeds through a free-radical
mechanism which involves an aryl radical as an intermedi-
ate. This method offers an excellent option for the syntheses
of biaryls.
Table 3 Direct arylation reactions of 4-iodoanisole with arenes a)
Supporting information
The supporting information is available online at chem.scichina.com and
link.springer.com/journal/11426. The supporting materials are published as
submitted, without typesetting or editing. The responsibility for scientific
accuracy and content remains entirely with the authors.
This work was financially supported by the National Basic Research Pro-
gram of China (2011CB932404, 2011CBA00501), and the National Natu-
ral Science Foundation of China (21332001, 21431008, 21301173).
1
(a) Evans DA, Dinsmore CJ, Watson PS, Wood MR, Richardson TI,
Trotter BW, Katz JL. Nonconventional stereochemical issues in the
design of the synthesis of the vancomycin antibiotics: challenges im-
a) Method A; b) isolated yields, isomeric ratios were determined by
NMR analysis; c) method B.

Kan et al. Sci China Chem July (2015) Vol.58 No.7
5
posed by axial and nonplanar chiral elements in the heptapeptide
133: 4243–4245
aglycons. Angew Chem Int Ed, 1998, 37: 2704–2708; (b) Cuccia LA,
Lehn JM, Homo JC, Schmutz M. Encoded helical self-organization
and self-assembly into helical fibers of an oligoheterocyclic pyri-
dine-pyridazine molecular strand. Angew Chem Int Ed, 2000, 39:
233–237; (c) Lehn JM. Toward self-organization and complex matter.
Science, 2002, 295: 2400–2403; (d) Laird T. What type of reactions
do process chemists use on scale? Org Process Res Dev, 2006, 10:
851–852; (e) Corbet JP, Mignani G. Selected patented cross-coupling
reaction technologies. Chem Rev, 2006, 106: 2651–2710
(a) de Meijere A, Diederich F. Metal-Catalyzed Cross-Coupling Re-
actions. 2nd Ed. Weinheim: Wiley-VCH, 2004; (b) Miyaura N.
Cross-Coupling Reactions. Topics in Current Chemistry. Berlin:
Springer, 2002; (c) Tsuji J. Transition Metal Reagents and Catalysts:
Innovaions in Organic Synthesis. Chichester: Wiley, 2002; (d) Hart-
wig JF. Organotransition Metal Chemistry: From Bonding to Cataly-
sis. Sauaslito: University Science Book, 2010
MacMillan DWC. The advent and development of organocatalysis.
Nature, 2008, 455: 304–308; (b) Bertelsen S, Jorgensen KA. Organo-
catalysis: after the gold rush. Chem Soc Rev, 2009, 38: 2178–2189
For rencent reviews, see: (a) Studer A, Curran DP. Organocatalysis
and C–H activation meet radical- and electron-transfer reactions. An-
gew Chem Int Ed, 2011, 50: 5018–5022; (b) Yanagisawa S, Itami K.
tert-Butoxide-mediated C–H bond arylation of aromatic compounds
with haloarenes. ChemCatChem, 2011, 3: 827–829; (c) Shirakawa E,
Hayashi T. Transition-metal-free coupling reactions of aryl halides.
Chem Lett, 2012, 41: 130–134; (d) Chan TL, Wu Y, Choy PY,
Kwong FY. A radical process towards the development of transition-
metal-free aromatic carbon-carbon bond-forming reactions. Chem
Eur J, 2013, 19: 15802; (e) Sun CL, Shi ZJ. Transition-metal-free
coupling reactions. Chem Rev, 2014, 114: 9219–9280
8
9
Prier CK, Rankic DA, MacMillan DWC. Visible light photoredox
catalysis with transition metal complexes: applications in organic
synthesis. Chem Rev, 2013, 113: 5322–5363
(a) Narayanam JMR, Stephenson CRJ. Visible light photoredox ca-
talysis: applications in organic synthesis. Chem Soc Rev, 2011, 40:
102–113; (b) Nagib DA, MacMillan DWC. Trifluoromethylation of
arenes and heteroarenes by means of photoredox catalysis. Nature,
2011, 480: 224–228; (c) Ye Y, Sanford MS. Merging visible-light
photocatalysis and transition-metal catalysis in the copper-catalyzed
trifluoromethylation of boronic acids with CF3I. J Am Chem Soc,
2012, 134: 9034–9037; (d) Schroll P, Hari DP, König B. Photocata-
lytic arylation of alkenes, alkynes and enones with diazonium salts.
ChemistryOpen, 2012, 1: 130–133; (e) Yasu Y, Koike T, Akita M.
Three-component oxytrifluoromethylation of alkenes: highly efficient
and regioselective difunctionalization of C=C bonds mediated by
photoredox catalysts. Angew Chem Int Ed, 2012, 51: 9567–9571; (f)
Nguyen JD, Tucker JW, Konieczynska MD, Stephenson CRJ. Inter-
molecular atom transfer radical addition to olefins mediated by oxi-
dative quenching of photoredox catalysts. J Am Chem Soc, 2011, 133:
4160–4163; (g) Tucker JW, Nguyen JD, Narayanam JMR, Krabbe
SW, Stephenson CRJ. Tin-free radical cyclization reactions initiated
by visible light photoredox catalysis. Chem Commun, 2010, 46:
4985–4987; (h) Kim H, Lee C. Visible-light-induced photocatalytic
reductive transformations of organohalides. Angew Chem Int Ed,
2012, 51: 12303–12306; (i) Zou YQ, Chen JR, Xiao WJ. Homoge-
neous visible-light photoredox catalysis. Angew Chem Int Ed, 2013,
52: 11701–11703; (j) Baralle A, Fensterbank L, Goddard JP, Ollivier
C. Aryl radical formation by copper(I) photocatalyzed reduction of
diaryliodonium salts: NMR evidence for a Cu(II)/Cu(I) mechanism.
Chem Eur J, 2013, 19: 10809–10813; (k) Xue QC, Xie J, Jin HM,
Cheng YX, Zhu CJ. Highly efficient visible-light-induced aerobic
oxidative C–C, C–P coupling from C–H bonds catalyzed by a
gold(III)-complex. Org Biomol Chem, 2013, 11: 1606–1609; (l) Wil-
lis MC, Hicke BJ, Uhlenbeck OC, Cech TR, Koch TH. Photocross-
linking of 5-iodouracil-substituted RNA and DNA to proteins. Sci-
ence, 1993, 262: 1255–1257
2
3
4
5
6
Yanagisawa S, Ueda K, Taniguchi T, Itami K. Potassium t-butoxide
alone can promote the biaryl coupling of electron-deficient nitrogen
heterocycles and haloarenes. Org Lett, 2008, 10: 4673–4676
(a) Shirakawa E, Itoh K, Higashino T, Hayashi T. tert-Butoxide-
mediated arylation of benzene with aryl halides in the presence of a
catalytic 1,10-phenanthroline derivative. J Am Chem Soc, 2010: 132,
15537–15539; (b) Sun CL, Li H, Yu DG, Yu M, Zhou X, Lu XY,
Huang K, Zheng SF, Li BJ, Shi ZJ. An efficient organocatalytic
method for constructing biaryls through aromatic C–H activation. Nat
Chem, 2010, 2: 1044–1049; (c) Liu W, Cao H, Zhang H, Chung KH,
He C, Wang H, Kwong FY, Lei AW. Organocatalysis in cross-
coupling: DMEDA-catalyzed direct C–H arylation of unactivated
benzene. J Am Chem Soc, 2010, 132: 16737–16740
10 (a) Hari DP, Schroll P, König B. Metal-free, visible-light-mediated
direct C–H arylation of heteroarenes with aryl diazonium salts. J Am
Chem Soc, 2012, 134: 2958–2961; (b) Kalyani D, McMurtrey KB,
Neufeldt SR. Sanford MS. Room-temperature C–H arylation: merger
of Pd-catalyzed C–H functionalization and visible-light photocataly-
sis. J Am Chem Soc, 2011, 133: 18566–18569; (c) Liu YX, Xue D,
Wang JD, Zhao CJ, Zou QZ, Wang C, Xiao JL. Room-temperature
arylation of arenes and heteroarenes with diaryliodonium salts by
photoredox catalysis. Synlett, 2013, 24: 507–513
11 (a) Sharma RK, Kharach N. The photolysis of iodoaromatic com-
pounds. Angew Chem Int Ed, 1968, 7: 36–44; (b) De Carolis MD,
Protti S, Fagnoni M, Albini A. Metal-free cross-coupling reactions of
aryl sulfonates and phosphates through photoheterolysis of aryl-
oxygen bonds. Angew Chem, 2005, 117: 1232–1236; (c) Dichiarante
V, Fagnoni M, Albini A. Metal-free synthesis of sterically crowded
biphenyls by direct Ar–H substitution in alkyl benzenes. Angew
Chem Int Ed, 2007, 46: 6495–6498; (d) verga D, Doria F, Pretali L,
Freccero M. Photoarylation of alkenes and heteroaromatics by di-
bromo-BINOLs in aqueous solution. J Org Chem, 2010, 75: 3477–
3480; (e) Linsenmeier AM. Williams CM, Bräse S. Synthesis of
phenanthridine derivatives via photolysis. J Org Chem, 2011, 76:
9127–9132; (f) Budén ME, Guastavino JF, Rossi RA. Room-tempe-
rature photoinduced direct C–H–arylation via base-promoted homo-
lytic aromatic substitution. Org Lett, 2013, 15: 1174–1177; (g) Zheng
XL, Yang L, Du WY, Ding AS, Guo H. Amine-catalyzed direct pho-
toarylation of unactivated arenes. Chem Asian J, 2014, 9: 439–442
12 Cheng YN, Gu XY, Li PX. Visible-light photoredox in homolytic
aromatic substitution: direct arylation of arenes with aryl halides. Org
Lett, 2013, 15: 2664–2667
7
(a) Qiu Y, Liu Y, Yang K, Hong W, Li Z, Wang Z, Yao Z, Jiang S.
New ligands that promote cross-coupling reactions between aryl hal-
ides and unactivated arenes. Org Lett, 2011, 13: 3556–3559; (b)
Yong GP, She WL, Zhang YM, Li YZ. Direct arylation of unactivat-
ed aromatic C–H bonds catalyzed by a stable organic radical. Chem
Commun, 2011, 47: 11766–11768; (c) Rueping M, Leiendecker M,
Das A, Poisson T, Bui L. Potassium tert-butoxide mediated Heck-
type cyclization/isomerization-benzofurans from organocatalytic rad-
ical cross-coupling reactions. Chem Commun, 2011, 47: 10629–10631;
(d) Vakuliuk O, Koszarna B, Gryko DT. Base-mediated direct aryla-
tion of pyrrole derivatives. Adv Synth Catal, 2011, 353: 925–930; (e)
Roman DS, Takahashi Y, Charette AB. Potassium tert-butoxide
promoted intramolecular arylation via a radical pathway. Org Lett,
2011, 13: 3242–3245; (f) Liu H, Yin B, Gao Z, Li Y, Jiang H. Tran-
sition-metal-free highly chemo- and regioselective arylation of unac-
tivated arenes with aryl halides over recyclable heterogeneous cata-
lysts. Chem Commun, 2012, 48: 203–-2035; (g) Chen WC, Hsu YC,
Shih WC, Lee CY, Chuang WH, Tsai YF, Chen PY, Ong TG. Metal-
free arylation of benzene and pyridine promoted by amino-linked ni-
trogen heterocyclic carbenes. Chem Commun, 2012, 48: 6702–6704; (h)
Zhao HQ, Shen J, Guo JJ, Ye RJ, Zeng HQ. A macrocyclic aromatic
pyridone pentamer as a highly efficient organocatalyst for the direct
arylations of unactivated arenes. Chem Commun, 2013, 49: 2323–
2325; (i) Truong T, Daugulis O. Base-mediated intermolecular sp2
C–H bond arylation via benzyne intermediates. J Am Chem Soc, 2011,
13 Schmidt LC, Arguello JE, Penenory AB. Nature of the chain propa-
gation in the photostimulated reaction of 1-bromonaphthalene with
sulfur-centered nucleophiles. J Org Chem, 2007, 72: 2936–2944