Ligand-Free Heck Reactions of Aryl Iodides: Significant Acceleration of the Rate through Visible Light Irradiation at Ambient Temperature

Article abstract of DOI:10.1002/adsc.201600704

A mild Heck reaction of aryl iodides and olefins was realized by the cooperation of a palladium and a photoredox catalyst under the irradiation of visible light. This protocol works well to synthesize stilbenes with high Z/E ratios and (E)-cinnamates in the absence of ligands at ambient temperature. Control experiments revealed that palladium salt, visible light and photoredox catalyst were all crucial for the achievement of this cross-coupling under mild conditions. (Figure presented.).

Full text of DOI:10.1002/adsc.201600704

COMMUNICATIONS
DOI: 10.1002/adsc.201600704
Ligand-Free Heck Reactions of Aryl Iodides: Significant
Acceleration of the Rate through Visible Light Irradiation at
Ambient Temperature
Heng Zhanga,b and Xueliang Huanga,*
a
Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, Peopleꢀs Republic of China
Fax : (+86)-591-6317-3587; phone: (+86)-591-6317-3587; e-mail: huangxl@fjirsm.ac.cn
University of Chinese Academy of Sciences, Beijing 100049, Peopleꢀs Republic of China
b
Received: July 4, 2016; Revised: September 8, 2016; Published online: && &&, 0000
Supporting information for this article can be found under: http://dx.doi.org/10.1002/adsc.201600704.
Abstract: A mild Heck reaction of aryl iodides and
olefins was realized by the cooperation of a palladi-
um and a photoredox catalyst under the irradiation
of visible light. This protocol works well to synthe-
size stilbenes with high Z/E ratios and (E)-cinna-
mates in the absence of ligands at ambient tempera-
ture. Control experiments revealed that palladium
salt, visible light and photoredox catalyst were all
crucial for the achievement of this cross-coupling
under mild conditions.
maceutical, bioactive and agrochemical molecules.[5]
Typically, the Heck reaction is carried out with a cata-
lytic amount of palladium catalyst along with a phos-
phine ligand, in the presence of a suitable base under
thermal conditions. Many alternative ligands bearing
different functionalities were also studied.[6] The role
of ligands was proven to be stabilization of the reac-
tive palladium species and facilitation of the action of
the elemental steps. However, most ligands suffer
from drawbacks of one kind or another, such as high
cost, potential sensitivity towards air or moisture, and
a need for multistep manipulations for their prepara-
tion.
Keywords: ambient temperature reaction; Heck re-
action; palladium catalysts; phosphine ligand-free
conditions; photoredox catalysts
In this context, (phosphine) ligand-free Heck reac-
tions have been intensively studied.[7] However, harsh
reaction conditions (heating), immobilization of the
catalyst, or special reaction media were required. Re-
cently, elegant works on the ligand-free Heck reac-
In recent years, visible-light photoredox catalysis to tions of electronically non-biased olefins were report-
activate organic compounds has emerged as a power- ed by Sigman and co-workers.[8] Although these reac-
ful tool for mild and environmentally benign organic tions are very effective, and could be carried out
transformations.[1] More intriguingly, merging photo- under mild conditions, the electrophiles employed
catalysis with transition metal catalysis can improve were limited to arenediazonium salts. PdCl2- or
the reaction efficiency of established organic transfor- Pd(OAc)2-catalyzed Heck reactions under UV-visible
mations and even accomplish novel organic transfor- light irradiation have also been reported.[9] Similarly,
mations.[2,3] In 2007, Osawa and co-workers found that heating, high energy light sources or additional li-
the Sonogashira reaction using the well known photo- gands cannot be avoided.[9c–e] Therefore, the develop-
catalyst tris(2,2’-bipyridyl)ruthenium(II) as cocatalyst ment of an operationally simple, ligand-free Heck re-
under UV/Vis irradiation showed much higher con- action that can carried out under mild condition is
versions than those conducted in the dark.[3a] Inspired highly desirable. Herein, we describe the merging of
by this study, we were encouraged to test the feasibili- palladium and photoredox catalysis that enables an
ty of phosphine ligand-free Heck reactions of aryl hal- efficient cross-coupling reaction of aryl iodides and
ides with the assistance of visible light irradiation, olefins at room temperature under visible light irradi-
which might lead to a more practical protocol for the ation without addition of ligand (Scheme 1).
synthesis of functionalized alkenes.
Initially, we examined the reaction of iodobenzene
The Heck reaction holds a fundamental place in or- 1a and ethyl acrylate 2a in the presence of a palladium
ganic chemistry for C–C bond formation.[4] It has source that had been found to be convenient and in-
been widely applied in the synthesis of various phar- expensive under a variety of reaction conditions
Adv. Synth. Catal. 0000, 000, 0 – 0
1
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
asc.wiley-vch.de
m(II) to palladium(0).[3a,9c,d] Thus, it is reasonable to
explain why the reaction was inhibited when run
under an atmosphere of oxygen (entry 6).[10] Addition
of 1.0 equivalent of 1,4-benzoquinone led to no for-
mation of 3a either (entry 10). To elucidate the mech-
anism of the current photochemical process, two radi-
cal inhibitors, namely 2,2,6,6-tetramethylpiperidinyl 1-
oxyl (TEMPO) and 2,6-di-tert-butyl-4-methylphenol
(BHT), were tested in the coupling reaction. The ad-
dition of one equivalent of TEMPO almost complete-
ly inhibited the reaction (entry 8). Conversely, the re-
action was not influenced by the addition of BHT
(entry 9). These seemingly contradictory observations
can be explained according to previous reports in
which TEMPO was employed as an oxidant to regen-
erate a palladium(II) catalyst.[11] Taken together, the
results obtained here indicate that a radical pathway
is unlikely, and a redox pathway via Pd(0)/Pd(II) is ar-
guably reasonable. Interestingly, in the presence of an
Scheme 1. Heck reactions. EWG=electron withdrawing
groups.
(Table 1). Ru(bpy)3Cl2·6H2O (1 mol%) was employed organic reductant, Hantzsch ester, and an inorganic
as the photocatalyst firstly, and blue LEDs were uti- base, K2CO3, the reaction could proceed equally well.
lized as the source of visible light. After a brief But omitting ether of the reagents led to a strikingly
screening of various solvents, palladium catalysts and low efficiency of the current Heck reaction (Table 2,
bases, it was found that using simple Pd(OAc)2 as the entry 11 vs. Table 1, entries 11 and 15). These out-
catalyst (1 mol%), Et3N as base, the current visible comes strongly suggest that NEt3 acts not just as
light-mediated Heck reaction could proceed smoothly a base but also as a reducing reagent. Thus replacing
at ambient temperature in DMF (N,N-dimethylforma- NEt3 with other bases led to lower conversion
mide) or NMP (N-methylpyrrolidin-2-one), giving the (Table 1, entry 2 vs. entries 13–15).
corresponding ethyl cinnamate 3a in nearly quantita-
With an effective set of conditions established, the
tive yield with complete E selectivity of the double generality and limitation of the current visible light-
bond (entries 2 and 10). It is worthwhile to mention mediated Heck reaction were examined by running
that common palladium(0) sources, such as Pd(PPh3)4 the reaction on a 1 mmol scale. As depicted, a wide
and Pd2(dba)3, proved to be inactive (entries 3 and 4). array of aryl iodides bearing electron-donating or
Further investigations on the effects of different pho- electron-withdrawing groups can react with ethyl ac-
tocatalysts were carried out (entries 16–19), and the rylate under standard conditions, providing (E)-cou-
results indicated that, besides Ru(bpy)3Cl2·6H2O, pling products in good to excellent yields (Table 3,
under otherwise identical conditions, the organic mol- 3a–3g). For the aryl iodides bearing strong electron-
ecule Rose Bengal could also facilitate the formation withdrawing substituents at the para position of the
of 3a (entry 17). Notably, the loading of both catalysts phenyl ring, such as an ester group, a higher catalyst
could be decreased to 0.5 mol%, without sacrificing loading of Pd(OAc)2 and prolonged reaction time
the reaction efficiency (entry 21). The current reac- were required (Table 3, 3g). Of note, the current
tion could also be performed in more concentrated ligand-free Heck reaction exhibited negligible effects
reaction media, while 3a was still obtained in excel- towards sterically hindered substituents. This phenom-
lent yield (entry 23). The reaction was inhibited when enon was evidenced by setting up a variety of groups
carried out under an atmosphere of air (entry 22). We with different electronics at the ortho position of the
have also tried to monitor the reaction temperature aryl iodides (Table 3, 3h, 3i, 3k, 3l, 3o, 3q, 3s and 3t).
during irradiation, and a negligible heating effect by Another remarkable feature was that the current
the lamp was observed.
transformation tolerated a variety of functional
Then, a series of control experiments was per- groups. Iodoanilines (1h, 1i and 1n) and iodophenols
formed (Table 2). The results revealed that the palla- (1m and 1o) were viable substrates. Furthermore, the
dium catalyst, light, photocatalyst and base were all current Heck reactions selectively took place for aryl
essential for the current Heck reaction (entries 2–5). iodides, keeping other halide groups (X=F, Cl, Br)
Replacing Ru(bpy)3Cl2·6H2O with 2,2’-bipyridine intact (3d–3f, 3p–3q). This offers the opportunity for
(bpy) led to no formation of 3a, which means that further synthetic manipulations. Beside acrylates,
Ru(bpy)3Cl2·6H2O does not act as a precursor of the pent-1-en-3-one could participate in the coupling re-
ligand (entry 7). It is well established that the UV- action as well, furnishing the corresponding enone 3v
visible light can promote the reduction of palladiu- in 95% yield. Pleasingly, the reaction of aliphatic ole-
Adv. Synth. Catal. 0000, 000, 0 – 0
2
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
asc.wiley-vch.de
Table 1. Screening of the optimal reaction conditions.[a]
[a]
Reaction conditions: iodobenzene (0.4 mmol), ethyl acrylate (0.8 mmol), Pd catalyst (0.004 mmol),
photoredox catalyst (0.004 mmol) and base (0.80 mmol) in solvent (4 mL), room temperature, 24 h,
irradiated by 0.72 W blue LEDs.
Yields determined by H NMR using CH2Br2 as the internal standard.
2a (0.48 mmol) was used.
Pd(OAc)2 (0.5 mg, 0.002 mmol) and Ru(bpy)3Cl2·6H2O (1.5 mg, 0.002 mmol) were used.
Reaction was performed under an atmosphere of air.
DMF (0.4 mL) was used.
[b]
[c]
[d]
[e]
[f]
1
fins, such as allylbenzene with aryl iodides and the in- ventional Heck reactions, (Z)-stilbene 5a was ob-
tramolecular cyclization of 1-(allyloxy)-2-iodobenzene tained as the major product after 72 hours. Rueping
proceeded smoothly, giving the coupling products 3w and co-workers reported a catalytic (E)- to (Z)-iso-
and 3x in 92% and 76% yields, respectively.
merization of olefins in the presence of different pho-
Subsequently, we applied the current photoredox- tosensitizers including Ru(bpy)3Cl2 under mild condi-
aided Heck coupling to the reaction of iodobenzene tions recently.[12] Thus we envisioned that a tandem
1a with styrene 4a. Surprisingly, compared to the con- process involving an (E)-isomer-selective Heck reac-
Adv. Synth. Catal. 0000, 000, 0 – 0
3
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
asc.wiley-vch.de
Table 2. Control experiments.
[a]
Reaction conditions: 1a (0.4 mmol), 2a (0.8 mmol), Pd(OAc)2 (0.9 mg, 0.004 mmol), Ru(b-
py)3Cl2·6H2O (3.0 mg, 0.004 mmol) and Et3N (0.80 mmol) in DMF (4 mL), room temperature, 24 h,
irradiated by 0.72 W blue LEDs.
Yields determined by H NMR using CH2Br2 as the internal standard.
See Table 1, entry 22.
bpy (2 mol%).
TEMPO (100 mol%).
BHT (100 mol%).
1,4-Benzoquinone (100 mol%).
K2CO3 (200 mol%) and Hantzsch ester (200 mol%).
[b]
[c]
[d]
[e]
[f]
1
[g]
[h]
tion and a visible light-promoted isomerization might iodides with styrenes bearing different substituents.
be possible. Indeed, on subjecting the commercially As depicted in Table 4, a library of (Z)-stilbenes 5
available (E)-stilbene 5a to the standard conditions, could be prepared in a highly efficient manner. An in-
(E)-5a was isomerized to the corresponding (Z)- creased Z/E ratio of 5 could be obtained by extending
isomer in 48 hours (Scheme 2).
the reaction time. Importantly, this domino process
This two-step, one-pot domino reaction represents also represents a rare example where the same photo-
an efficient catalytic approach for the synthesis of 1,2- catalyst could behave distinctively in a tandem reac-
disubstituted (Z)-olefins which are not easy to obtain tion at different stages.
via traditional methods.[13,14] Gratifyingly, this protocol
To investigate the reaction process, we used 1-
could be applied to the reaction of a variety of aryl fluoro-4-iodobenzene and styrene 4a as substrates to
monitor the reaction processes under different condi-
tions. The coupling reaction was complete within 25 h
under the standard conditions, and (Z)-5f was ob-
tained as the major product (Figure 1, A). In compari-
son, in the absence of Ru catalyst, low conversions of
both reactants were observed after 25 h. According to
the light switched on and off experiments (Figure 1,
B), the reaction rate was accelerated significantly
only during the irradiated period, while the reaction
Scheme 2. Isomerization of (E)-5a.
was almost shut down during the dark period. These
Adv. Synth. Catal. 0000, 000, 0 – 0
4
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
asc.wiley-vch.de
Table 3. Reaction scope of aryl iodides with ethyl acrylate and other olefins.[a]
[a]
Reaction conditions: aryl iodide (1.0 mmol), olefin (2.0 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), Ru(bpy)3Cl2·6H2O
(7.5 mg, 0.01 mmol) and Et3N (2.0 mmol), DMF (1 mL), room temperature, blue LEDs. Yields are referred to isolated
pure compounds.
Pd(OAc)2 (11.2 mg, 0.05 mmol) was used.
[b]
results suggest that, for this reaction, the regeneration scale synthetic utility. The reaction exhibits exclusive
of active palladium catalyst is accelerated during the (E)-selectivity for the coupling of aryl iodides with
period of irradiation.
acrylates. Strikingly, when styrenes were employed as
To confirm whether the nanoparticulate nature of the reaction partners, isomerization of the products
the palladium catalyst was responsible for the visible from (E)- to (Z)-isomers would take place, giving
light-assisted Heck reaction, a mercury drop experi- (Z)-stilbenes in highly selective manner. Preliminary
ment was conducted and resulted in a significant in- mechanistic studies revealed that the photo and palla-
hibition for the conversion of 1a (Scheme 3). TEM dium catalysts played critical roles for the current
(transmission electron microscopy) analysis and XRD transformation. Moreover, according to the mercury
(X-ray diffraction) tests were also performed and re- drop experiments, palladium nanoparticles were pro-
vealed that Pd nanoparticles were produced during duced during the reaction.
the process (see the Supporting Information).[7q,9e,15]
Further studies are clearly required to determine the
exact role of the resulting palladium nanoparticles.
Experimental Section
In conclusion, we have developed an operationally
simple, visible light-mediated Pd-Ru-catalyzed Heck
reaction. The salient features are ligand-free, mild re-
action conditions (ambient temperature), broad sub-
strate scope which tolerates a variety of functional
General Procedure
A dry Schlenk tube equipped with a stir bar was charged
with aryl iodide (1.0 mmol), olefin (2.0 mmol), Et3N
groups, thus rendering a great potential for the large (2.0 mmol), Pd(OAc)2 (0.01/0.05 mmol), Ru(bpy)3Cl2·6H2O
Adv. Synth. Catal. 0000, 000, 0 – 0
5
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
asc.wiley-vch.de
Table 4. Preparation of different (Z)-stilbenes 5.[a]
Scheme 3. Mercury drop experiment.
monitored by TLC, the crude mixture was poured into H2O
and extracted with ethyl acetate. The organic layer was
washed with brine, dried over Na2SO4, and concentrated.
The residue was purified by column chromatography on
silica gel to give the desired product.
Acknowledgements
We thank the financial support by NSFC (Grant No.
21402197, 21502190), NSF of Fujian (Grant No.
2015J05043), Hundred-Talent Program and the Strategic Pri-
ority Research Program of the Chinese Academy of Sciences
(Grant No. XDB20000000). We also thank Dr. Gui Chen for
helpful suggestions.
[a]
Reaction conditions: aryl iodide (0.5 mmol), olefin
(1.0 mmol), Pd(OAc)2 (5.6 mg, 0.025 mmol), Ru(b-
py)3Cl2·6H2O (11.3 mg, 0.015 mmol) and triethylamine
(1.0 mmol), DMF (5 mL).
Isolated yields.
The reaction time was extended to 72 h.
[b]
[c]
References
[1] For some reviews on visible light photocatalysis, see:
a) R. A. Angnes, Z. Li, C. R. Correia, G. B. Hammond,
Org. Biomol. Chem. 2015, 13, 9152; b) T. P. Yoon,
M. A. Ischay, J. Du, Nat. Chem. 2010, 2, 527; c) F.
´
Teply, Collect. Czech. Chem. Commun. 2011, 76, 859;
d) D. M. Schultz, T. P. Yoon, Science 2014, 343,
1239176; e) J. M. Narayanam, C. R. Stephenson, Chem.
Soc. Rev. 2011, 40, 102; f) C. K. Prier, D. A. Rankic,
D. W. C. MacMillan, Chem. Rev. 2013, 113, 5322; g) J.
Xuan, W. -J. Xiao, Angew. Chem. 2012, 124, 6934;
Angew. Chem. Int. Ed. 2012, 51, 6828; h) D. P. Hari, B.
Konig, Angew. Chem. 2013, 125, 4832; Angew. Chem.
Int. Ed. 2013, 52, 4734; i) K. L. Skubi, T. R. Blum, T. P.
Yoon, Chem. Rev. 2016, 116, 10035; j) D. Ravelli, S.
Protti, M. Fagnoni, Chem. Rev. 2016, 116, 9850.
[2] a) T. Noꢂl, Green Process Synth. 2013, 2, 531; b) A.
Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser,
A. von Zelewsky, Coord. Chem. Rev. 1988, 84, 85; c) A.
Inagaki, M. Akita, Coord. Chem. Rev. 2010, 254, 1220;
d) M. N. Hopkinson, B. Sahoo, J. L. Li, F. Glorius,
Chem. Eur. J. 2014, 20, 3874; e) A. Inagaki, H. Nakaga-
wa, M. Akita, K. Inoue, M. Sakai, M. Fujii, Dalton
Trans. 2008, 6709.
[3] For selected examples with palladium catalysis, see:
a) M. Osawa, H. Nagai, M. Akita, Dalton Trans. 2007,
827; b) D. Kalyani, K. B. McMurtrey, S. R. Neufeldt,
M. S. Sanford, J. Am. Chem. Soc. 2011, 133, 18566;
c) S. R. Neufeldt, M. S. Sanford, Adv. Synth. Catal.
2012, 354, 3517; d) S. B. Lang, K. M. OꢀNele, J. A.
Tunge, J. Am. Chem. Soc. 2014, 136, 13606; e) J. Xuan,
T.-T. Zeng, Z.-J. Feng, Q.-H. Deng, J.-R. Chen, L.-Q.
Lu, W.-J. Xiao, H. Alper, Angew. Chem. 2015, 127,
Figure 1. Process experiments of Heck coupling reactions of
1-fluoro-4-iodobenzene and styrene. A: reaction of 1-fluoro-
4-iodobenzene with styrene under standard conditions. B:
Light switched on and off experiment.
(0.01/0.03 mmol) and DMF (1 mL) under argon, then cooled
by liquid nitrogen, evacuated by vacuum pump and backfil-
led with argon for three times. The solution was stirred at
room temperature under irradiation with blue LEDs
(0.72 W) for 24 h. Upon completion of the reaction, as
Adv. Synth. Catal. 0000, 000, 0 – 0
6
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
asc.wiley-vch.de
1645; Angew. Chem. Int. Ed. 2015, 54, 1625. With
copper catalysis, see: f) Y. Ye, M. S. Sanford, J. Am.
Chem. Soc. 2012, 134, 9034; g) Y. Ye, S. A. Kunzi, M. S.
Sanford, Org. Lett. 2012, 14, 4979. With gold catalysis,
see: h) B. Sahoo, M. N. Hopkinson, F. Glorius, J. Am.
Chem. Soc. 2013, 135, 5505; i) X. Z. Shu, M. Zhang, Y.
He, H. Frei, F. D. Toste, J. Am. Chem. Soc. 2014, 136,
5844; j) M. N. Hopkinson, B. Sahoo, F. Glorius, Adv.
Synth. Catal. 2014, 356, 2794. With nickel catalysis, see:
k) Z. Zuo, D. T. Ahneman, L. Chu, J. A. Terrett, A. G.
Doyle, D. W. C. MacMillan, Science 2014, 345, 437;
l) J. C. Tellis, D. N. Primer, G. A. Molander, Science
2014, 345, 433; m) L. Chu, J. M. Lipshultz, D. W. C.
MacMillan, Angew. Chem. 2015, 127, 8040; Angew.
Chem. Int. Ed. 2015, 54, 7929 .
2002, 4, 4399; g) A. H. M. de Vries, F. J. Parlevliet, L.
Schmieder-Van de Vondervoort, J. H. M. Mommers,
H. J. W. Henderickx, M. A. M. Walet, J. G. de Vries,
Adv. Synth. Catal. 2002, 344, 996; h) A. H. M. de Vries,
J. M. C. A. Mulders, J. H. M. Mommers, H. J. W. Hen-
derickx, J. G. de Vries, Org. Lett. 2003, 5, 3285; i) J. G.
de Vries, Dalton Trans. 2006, 421; j) D. Pan, A. Chen,
Y. Su, W. Zhou, S. Li, W. Jia, J. Xiao, Q. Liu, L. Zhang,
N. Jiao, Angew. Chem. 2008, 120, 4807; Angew. Chem.
Int. Ed. 2008, 47, 4729; k) S. B. Waghmode, S. S. Arbuj,
B. N. Wani, C. S. Gopinath, Can. J. Chem. 2013, 91, 348.
[8] a) S. Engupta, S. Bhattacharyya, Tetrahedron Lett.
1995, 36, 4475; b) E. W. Werner, M. S. Sigman, J. Am.
Chem. Soc. 2011, 133, 9692; c) J. Salabert, R. M. Sebas-
tiꢃn, A. Vallribera, J. F. Cꢄvicos, C. Nꢃjera, Tetrahedron
2013, 69, 2655.
[4] a) R. F. Heck, J. Am. Chem. Soc. 1969, 91, 6707;
b) R. F. Heck, J. P. Nolley, J. Org. Chem. 1972, 37,
2320; c) R. F. Heck, Acc. Chem. Res. 1979, 12, 146;
d) W. Cabri, I. Candiani, Acc. Chem. Res. 1995, 28, 2;
e) J. Tsuji, Palladium Reagents, Catalysis, Wiley, Chi-
chester, 1995; f) R. F. Heck, Palladium Reagents in Or-
ganic Synthesis; Academic Press, London, 1985.
[5] a) B. Cornils, W. A. Herrmann, Applied Homogeneous
Catalysis with Organometallic Compounds: A Compre-
hensive Handbook in Two Volumes, VCH, Weinheim,
New York, 1996; b) A. Zapf, M. Beller, Top. Catal.
2002, 19, 101; c) S. J. Danishefsky, J. J. Masters, W. B.
Young, J. T. Link, L. B. Snyder, T. V. Magee, D. K.
Jung, R. C. A. Isaacs, W. G. Bornmann, C. A. Alaimo,
C. A. Coburn, M. J. Di Grandi, J. Am. Chem. Soc. 1996,
118, 2843; d) I. P. Beletskaya, A. V. Cheprakov, Chem.
Rev. 2000, 100, 3009; e) A. B. Dounay, L. E. Overman,
Chem. Rev. 2003, 103, 2945; f) A. De Meijere, F. E.
Meyer, Angew. Chem. 1994, 106, 2473; Angew. Chem.
Int. Ed. 1994, 33, 2379.
[6] For selected examples, see: a) D. E. Bergbreiter, P. L.
Osburn, A. Wilson, E. M. Sink, J. Am. Chem. Soc.
2000, 122, 9058; b) C. Rocaboy, J. A. Gladysz, Org.
Lett. 2002, 4, 1993; c) D. A. Alonso, C. Najera, M. C.
Pacheco, Org. Lett. 2000, 2, 1823; d) M. B. Andrus, C.
Song, J. Zhang, Org. Lett. 2002, 4, 2079; e) A.-E. Wang,
J.-H. Xie, L.-X. Wang, Q.-L. Zhou, Tetrahedron 2005,
61, 259; f) M. L. Kantam, P. Srinivas, J. Yadav, P. R.
Likhar, S. Bhargava, J. Org. Chem. 2009, 74, 4882; g) Y.
Wang, J. Luo, Z. Liu, J. Organomet. Chem. 2013, 739,
1; h) C. Gurtler, S. L. Buchwald, Chem. Eur. J. 1999, 5,
3107; i) M. Ohff, A. Ohff, D. Milstein, Chem. Commun.
1999, 357.
[7] For selected examples, see: a) T. Jeffery, J. Chem. Soc.
Chem. Commun. 1984, 1287; b) C. Gozzi, L. Lavenot,
K. Ilg, V. Penalva, M. Lemaire, Tetrahedron Lett. 1997,
38, 8867; c) M. T. Reetz, E. Westermann, Angew.
Chem. 2000, 112, 170; Angew. Chem. Int. Ed. 2000, 39,
165; d) L. Djakovitch, K. Koehler, J. Am. Chem. Soc.
2001, 123, 5990; e) K. Okubo, M. Shirai, C. Yokoyama,
Tetrahedron Lett. 2002, 43, 7115; f) S. Chandrasekhar,
C. Narsihmulu, S. S. Sultana, N. R. Reddy, Org. Lett.
[9] Reports on UV-visible light-promoted Heck reactions,
see: a) A. R. Chaudhary, A. V. Bedekar, Tetrahedron
Lett. 2012, 53, 6100; b) G. Imperato, B. Konig, Chem-
AHCTUNGTREGSNNUN usChem 2008, 1, 993; c) M. A. Fredricks, M. Drees, K.
Kçhler, ChemCatChem 2010, 2, 1467; d) M. A. Fre-
dricks, K. Kçhler, Catal. Lett. 2009, 133, 23; e) S. B.
Waghmode, S. S. Arbuj, B. N. Wani, C. S. Gopinath,
Can. J. Chem. 2013, 91, 348; f) M. S. Oliveira, D. Sever-
ino, F. M. Prado, J. P. F. Angeli, F. D. Motta, M. S. Bap-
tista, M. H. G. Medeiros, P. D. Mascio, Photochem.
Photobiol. Sci. 2011, 10, 1546.
[10] a) J. Zoller, D. C. Fabry, M. A. Ronge, M. Rueping,
Angew. Chem. 2014, 126, 13480; Angew. Chem. Int. Ed.
2014, 53, 13264; b) D. C. Fabry, M. A. Ronge, J. Zoller,
M. Rueping, Angew. Chem. 2015, 127, 2843; Angew.
Chem. Int. Ed. 2015, 54, 2801.
[11] For examples on the use of TEMPO as an oxidant in
Pd-catalyzed reactions, see: a) S. Kirchberg, R. Froeh-
lich, A. Studer, Angew. Chem. 2009, 121, 4299; Angew.
Chem. Int. Ed. 2009, 48, 4235; b) K. Mitsudo, T. Kaide,
E. Nakamoto, K. Yoshida, H. Tanaka, J. Am. Chem.
Soc. 2007, 129, 2246; c) S. Kirchberg, T. Vogler, A.
Studer, Synlett 2008, 2841; d) K. Mitsudo, T. Ishii, H.
Tanaka, Electrochemistry 2008, 76, 859; e) K. Mitsudo,
T. Shiraga, D. Kagen, D. Shi, Y. Becker, J. H. Tanaka,
Tetrahedron 2009, 65, 8384.
[12] a) D. C. Fabry, M. A. Ronge, M. Rueping, Chem. Eur.
J. 2015, 21, 5350; b) M. Osawa, M. Hoshino, Y. Wakat-
suki, Angew. Chem. 2001, 113, 3580; Angew. Chem. Int.
Ed. 2001, 40, 3472.
[13] a) L. F. V. Staden, D. Gravestock, D. J. Ager, Chem.
Soc. Rev. 2002, 31, 195; b) P. A. Byrne, D. G. Gilheany,
Chem. Soc. Rev. 2013, 42, 6670; c) E. Negishi, Z.
Huang, G. Wang, S. Mohan, C. Wang, H. Hattori, Acc.
Chem. Res. 2008, 41, 1474.
[14] a) K. Maruoka, M. Oishi, H. Yamamoto, J. Am. Chem.
Soc. 1996, 118, 2289; b) S. J. Meek, R. V. OꢀBrien, J.
Llaveria, R. R. Schrock, A. H. Hoveyda, Nature 2011,
471, 461; c) Y. Liu, L. Hu, H. Chen, H. Du, Chem. Eur.
J. 2015, 21, 3495.
[15] L. Zheng, J. Li, J. Phys. Chem. B 2005, 109, 1108.
Adv. Synth. Catal. 0000, 000, 0 – 0
7
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
8 Ligand-Free Heck Reactions of Aryl Iodides: Significant
Acceleration of the Rate through Visible Light Irradiation
at Ambient Temperature
Adv. Synth. Catal. 2016, 358, 1 – 8
Heng Zhang, Xueliang Huang*
Adv. Synth. Catal. 0000, 000, 0 – 0
8
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!