Metal-Free Direct α-Selective Arylation of Boron Dipyrromethenes via Base-Mediated C-H Functionalization

Article abstract of DOI:10.1021/acs.orglett.5b03706

A metal-free direct α-selective arylation of BODIPYs has been developed based on base-mediated C-H functionalization with easily accessible diaryliodonium salts, which provides a straightforward facile access to a variety of α-arylBODIPY dyes. The α-regioselectivity was confirmed by X-ray analysis, and was studied by DFT calculation. The resultant dyes show strong absorption and emission over a broad range of spectra tunable via the simple variation of the diaryliodonium salts. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.orglett.5b03706

Letter
pubs.acs.org/OrgLett
Metal-Free Direct α‑Selective Arylation of Boron Dipyrromethenes
via Base-Mediated C−H Functionalization
Xin Zhou, Qinghua Wu, Yang Yu, Changjiang Yu, Erhong Hao, Yun Wei, Xiaolong Mu, and Lijuan Jiao*
Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials, School of
Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, China
S
* Supporting Information
ABSTRACT: A metal-free direct α-selective arylation of BODIPYs has
been developed based on base-mediated C−H functionalization with easily
accessible diaryliodonium salts, which provides a straightforward facile access
to a variety of α-arylBODIPY dyes. The α-regioselectivity was confirmed by
X-ray analysis, and was studied by DFT calculation. The resultant dyes show
strong absorption and emission over a broad range of spectra tunable via the
simple variation of the diaryliodonium salts.
a
ODIPY (4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes
Scheme 1. Synthesis of α-ArylBODIPYs
B
have found wide applications in highly diverse research
fields,1 forexample,aslabelingreagentsandprobesinbiology2 and
as energy-transfer cassettes in material science,3 due to their
remarkable photophysical properties such as large molar
absorptivity, sharp fluorescence emissions, high fluorescence
quantum yields, and high photostability. These photophysical
properties can be finely tunable via the structural variations based
on their rich chemistry.4,5 For example, the installation of aryl
groups onto the α-position(s) of the BODIPY chromophore has
beenwidelyusedtoextendtheπ-conjugationofthechromophore
and to achieve long-wavelength dyes.
Traditionally,mostα-arylBODIPYsweregeneratedeitherfrom
de novo synthesis of α-arylpyrroles6 (Scheme 1a) or from the
transition-metal-catalyzed α-arylation on halogenated BODIPY
dyes7 (Scheme 1b). Later, Dehaen and co-workers8 reported the
improved efficient synthesis of α-arylBODIPYs based on
palladium-catalyzed C−H activation of BODIPY chromophore
(Scheme 1c). Recently, the first radical reaction on BODIPY by
Dehaen and co-workers provided a direct access to α-
arylBODIPYs using aryldiazonium salts mediated by ferrocene
(Scheme 1d).9 Nevertheless, these above elegant methods still
required the assistance of metal catalyst or promoters.
Hypervalent iodine(III) compounds have recently been
demonstrated as efficient reagents for a wide range of trans-
formations.10 These readily available diaryliodonium salts are
nontoxic, bench stable, and highly reactive and have been applied
for the regioselective electrophilic arylation of various nucleo-
philes in the presence of various transition metals or under metal-
free conditions, for example, arylation of indoles with Cu-
(OTf)2,11a,b or metal-free conditions11c and simple arenes with
platinum, copper, or palladium salts.11d−f Herein we report a
metal-free, highly regioselective, direct α-arylation of BODIPY
chromophores with easily accessible diaryliodonium salts. The
regioselectivity wasconfirmedbyX-ray analysisand maycomevia
a radical process. These resultant α-arylBODIPYs show strong
absorption and emission over a broad range of spectra that are
tunable via the simple variation of the diaryliodonium salts.
a
From (a) de novo synthesis of 2-arylpyrroles, (b) transition-metal-
catalyzed coupling reaction on 3,5-dihalogenoBODIPYs, (c) and (d)
metal-catalyzed/mediated C−H arylation of the BODIPY core, and
(e) the metal-free direct C−H Arylation of the BODIPY core with
diaryliodonium salts presented in this work.
Initially, we attempted the reaction between BODIPY 2 and a
stoichiometric amount of diphenyliodonium salt 3a in 1,2-
dichloroethane (Table S1). In the presence of 1.5 equiv of K2CO3
(entry 2), a major product was obtained in 13% isolated yield and
was confirmed to be the α-arylBODIPY 1a according to X-ray
analysis (Figure 1a). In the absence of base, only atrace amount of
1a was detected from this reaction (entry 1, Table S1). A set of
common organic solvents and inorganic bases were studied to
achieve the optimized reaction conditions (entries 3−11, Table
S1). Among those, use of 1,2-dichloroethane as solvent and
NaOH as base gave the best result (entry 10, Table S1). We also
investigated the influence of reagent ratio on this reaction. The
optimized reaction conditions were set to be 1.5 equiv of 3a and
NaOH with respect to BODIPY 2, respectively, in refluxing 1,2-
dichloroethane.
A further increase in the number of equivalents of 3a decreased
the yield of 1a with the appearance of 3,5-diphenylBODIPY 4a
(Table S1). The optimized ratio of 3a for the diarylation reaction
Received: December 30, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b03706
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 3. Regioselective α-Arylation of BODIPY 2 with
Unsymmetric Diaryliodonium Salts 3h−k
Figure 1. X-ray structures of 1a (a), 1e (b), and 4a (c). Key: C, gray; H,
light gray; O, red; N, blue; B, dark yellow; F, green.
was 3 equiv. At this ratio, 3,5-diphenylBODIPY 4a was obtained
regioselectively in 41% isolated yield (Scheme 2). The
regioselectivity of this diarylation was also confirmed by X-ray
analysis (Figure 1c). A further increase in the number of
equivalents of 3a only led to a decrease of the yield of 4a. No
tri- or multiphenylated products were observed.
generated in a relatively lower (37%) yield with respect to that of
meso-mesitylBODIPY 2.
Whenunsymmetricdiaryliodoniumsalts(3hand3i,Scheme3)
were used for this reaction, a high chemoselectivity, closely
associated with the steric hindrance and electronic effects of the
aryl groups, was observed. When 3h containing phenyl and meso-
mesityl groups was used for this reaction, only the less bulky
phenyl group was installed onto the α-position of the BODIPY
core. This result, however, did not follow the ortho-effect with
sterically hindered salts as previously reported12a−c and further
illustrated the delicate balance between steric and electronic
effects.12d The use of 3i containing both the phenyl and the
thiophenegroups forthereactiongavethesamearylationproduct
1a in a compatible yield. The chemoselectivity observed here was
in good agreement with previously reported selectivities, and
electron-poor aryl groups were transferred prefentially over
electron-rich aryl groups under metal-free conditions.12 These
unsymmetric diaryliodonium salts provide alternative arylation
reagents when the symmetric diaryliodonium salts were hard to
access. For example, electron-poor aryl groups, such as 3-
nitrophenyl and pyridium derivatives, were selectively installed
on the BODIPY core from 3j and 3k, giving 1i and 1j in 22% and
27% yields, respectively (Scheme 3).
To test the versatility of this α-arylation reaction, we further
applied a set of diaryliodonium salts 3b−e (Figure S1) containing
either moderate electron-withdrawing groups (such as the chloro
andbromogroupsin3band3c)orelectron-donatingsubstituents
(such as the tert-butyl and methoxy groups in 3d and 3e) for this
reaction. All of these functional groups were able to survive this
reaction. Under the optimized reaction conditions, the desired α-
arylBODIPYs 1b−e and their corresponding 3,5-diaryBODIPYs
4b−e were regioselectively obtained in 39−63% and 23−46%
isolated yields with 1.5 and 3 equiv of diaryliodonium salts 3,
respectively(Scheme2).Heteroaromatichypervalentiodiumsalt,
such as di(thiophene-2-yl)iodonium salt 3f, was also suitable for
this reaction and regioselectively generated the desired α-
thienylBODIPY 1f and 3,5-dithienylBODIPY 4f in 37% and
23% isolated yields, respectively. Compared with 3a−f, diary-
liodonium salt 3g with an o-methyl group showed lower reactivity
in this reaction due to steric hindrance and gave 1g in 17% yield.
Besidesmeso-mesitylBODIPY2,unsymmetricalmeso-HBODIPY
5 (Figure S1), possessing only one free α-position, was also
applicable for this reaction, from which 1h (Scheme 2) was
Scheme 2. Synthesis of Mono- and DiarylBODIPYs 1 and 4 from the Reaction of α-Free BODIPYs with Easily Accessible
Diaryliodonium Salts 3 under Metal-Free Conditions
a
b
c
d
Isolated yields. absorption maxima. emission maxima. fluorescence quantum yield.
B
DOI: 10.1021/acs.orglett.5b03706
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Crystals for BODIPYs 1a, 1e, and 4a (Figure 1) suitable for X-
ray analysis were obtained via the slow diffusion of petroleum
ether into the dichloromethane solutions of these dyes under
atmospheric pressure. As usual, each of these arylated BODIPYs
showan almost planar structure forthe BODIPY core(the central
six-membered C3N2B ring with two adjacent five-membered
pyrrole rings) with the plane defined by F−B−F atoms
perpendicular to that of the BODIPY core. The dihedral angle
between the meso-mesityl group and the BODIPY core is around
81°, 74°, and 87° for 1a, 1e, and 4a, respectively. The dihedral
angle between the α-aryl group(s) and the BODIPY core is 37°,
35°, and ∼40° for 1a, 1e, and 4a, respectively. The B−N distance
for these BODIPYs is within 1.54−1.55 Å, which indicates the
usual delocalization of the positive charge. In the solid state, there
are multiple C−H···F intermolecular hydrogen bonds between F
atoms and methyl hydrogens with the bond distance in the range
of 2.07−2.84 Å (Table S2).
Scheme 5. Proposed Reaction Mechanism for the
Regioselective α-Arylation of BODIPY 2 (Route a, with Solid
Lines) and Its Possible Competitive Radical Reaction Pathway
(Routeb,withDashedLines)fortheRegioselectiveFormation
of β-ArylBODIPYs
According to the mesomeric structures of BODIPY 2 (Figure
S3), the 2,6-(β-) positions of the BODIPY core bear the least
positive charge and should be most susceptible to electrophilic
attack as demonstrated in the regioselective formylation,
halogenation, sulfonation, and nitration reactions.13 Surprisingly,
this arylation reaction occurs regioselectively at the α-position of
the BODIPY chromophore. No expected β-arylated product was
detected. This interesting regioselectivity led us to further
investigate the reaction mechanism for this reaction.
Since decomposition of diaryliodonium salts to generate aryl
radicalshasbeendisclosedintheliterature,14 weproposedthatour
regioselective α-arylation would come through a radical process.
To test our hypothesis, a radical inhibitor, BHT (2,6-di-tert-butyl-
4-methylphenol), was added into the reaction mixture (Scheme
4). No reaction was detected even at an extended reaction period.
This indicates a possible radical reaction pathway for this α-
arylation(routea, Scheme5). Itinvolvesthegenerationofthearyl
radical species from the decomposition of diaryliodonium salts 3
and its further reaction with BODIPY 2 at the α-position to form
intermediateA.Subsequently,Areactswithdiaryliodoniumsalts3
to generate intermediate B and releases aryl radical species. In the
finalstep, hydroxideanion(fromthebase)attacksthe α-protonof
B to restore the aromaticity of the pyrrolic unit to form target α-
arylBODIPY 1 and release aryl iodide.
After considering the steric hindrance effect from the meso-
mesityl group, theoretically, there are still two possible
competitive radical reaction pathways available for this arylation
reaction (routes aand b, Scheme 5). To understand the reason for
the regioselective formation of α-arylBODIPY 1 instead of its
competitive product (β-arylBODIPY C) as observed in the
experiment, a computational study at the B3LYP/6-31G(d) level
using the Gaussian 09 program was performed on the reaction of
BODIPY 2 with phenyl radical, and the energy profiles are
depicted in Figure 2. The formation of the transition state TS2
(route b) requires an activation energy of 13.5 kcal/mol, which is
3.3 kcal/mol higher than that required for the formation of
transition state TS1 (route a). Furthermore, intermediate A is
more stable (by 13.3 kcal/mol) than A′. Therefore, the calculated
Figure 2. Free energy profiles for the two competitive radical reaction
pathways (routes a and b in Scheme 5) in the radical reaction of BODIPY
2 and the in situ generated phenyl radical at 298.15 K: structures of
transition states TS1 (route a) and TS2 (route b), structures of the
intermediates A (route a) and A′ (route b), and their corresponding
activation free energies.
energy profiles are in good agreement with the experimental
results,whichclearlyindicatethattheformationofα-arylBODIPY
1 (via route a) is energetically more favorable than that of β-
arylBODIPY C (via route b). Possible reaction at the meso-
position (route c in Scheme S2) was also investigated. The
energies of both the transition state and intermediate A″ are also
higher than those at the a-position. Further attempts to install an
aryl group on the BODIPY meso-position with 3,5-disubstituted
BODIPYs 6 and 7 failed (Scheme S2).
Photophysical properties of these resultant α-arylBODIPYs
were investigated in dichloromethane and are summarized in
Table S3. As demonstrated in Figure 3, α-arylation led to a
Scheme 4. Influence of BHP on This Arylation Reaction
Figure 3. Overlaid normalized absorption (solid lines) and fluorescence
emission (dashed lines) spectra of 2 (black), 1f (red), and 4f (blue) in
dichloromethane at room temperature.
C
DOI: 10.1021/acs.orglett.5b03706
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(4) Boens, N.; Verbelen, B.; Dehaen, W. Eur. J. Org. Chem. 2015, 2015,
6577.
(5) (a) Golf, H. R.; Reissig, H.; Wiehe, A. Org. Lett. 2015, 17, 982.
significant red-shift of the absorption and emission maxima with
respect to the starting BODIPY 2. In comparison to 2,
monoarylation (BODIPYs 1a−f) generally led to an around
30−60nmred-shiftoftheabsorptionandemissionmaxima, while
diarylation (BODIPYs 4a−f) provided an additional red-shift of
theabsorptionandemissionmaxima(upto60nm)withrespectto
the corresponding monoarylation ones. These mono- and di-α-
arylBODIPYs all show intense fluorescence emission (0.7 < Φ <
0.9). As shown in Figure S4, the absorption and emission maxima
can be easily tuned via the variation of the electronic properties of
the aryl group(s) in the diaryliodonium salts 3: the increase of the
electrondensityofthearylgroup(s)ledtoagradualred-shiftofthe
spectra.
In conclusion, a general and facile synthesis of a set of mono-
and di-α-arylBODIPYs was developed on the basis of a base-
mediated direct C−H α-arylation in refluxing 1,2-dichloroethane
with easily accessible diaryliodonium salts under metal-free
conditions. This regioselective α-arylation reaction may come
through a radical process. The resultant α-arylBODIPYs showed
strong absorption and intense fluorescence emission over a broad
range of the spectra and may be easily tuned via the variation of
diaryliodonium salts.
(b) Golf, H. R.; Reissig, H.; Wiehe, A. J. Org. Chem. 2015, 80, 5133.
(c) Palao, E.; de la Moya, S.; Agarrabeitia, A. R.; Esnal, I.; Banuelos, J.;
̃
Lop
́
ez -Arbeloa, A.; Ortiz, M. J. Org. Lett. 2014, 16, 4364. (d) Palao, E.;
Agarrabeitia, A. R.; Esnal, I.; Banuelos-Prieto, J.; Lop
́
ez, T. A.; Lopez
́
̃
-Arbeloa, I.; Armesto, D.; Ortiz, M. J. Org. Lett. 2013, 15, 4454. (e) Yokoi,
H.; Hiroto, S.; Shinokubo, H. Org. Lett. 2014, 16, 3004. (f) Buyukcakir,
O.; Bozdemir, O. A.;Kolemen, S.;Erbas, S.; Akkaya, E. U. Org. Lett. 2009,
11, 4644. (g) Ulrich, G.; Ziessel, R.; Haefele, A. J. Org. Chem. 2012, 77,
4298. (h) Ulrich, G.; Haefele, A.; Retailleau, P.; Ziessel, R. J. Org. Chem.
2012, 77, 5036.
(6) (a) Burghart, A.; Kim, H.; Welch, M. B.; Thoresen, L. H.;
Reibenspies,J.;Burgess,K.J.Org.Chem.1999,64,7813.(b)Zaitsev,A.B.;
Meallet-Renault,R.;Schmidt,E.Y.;Mikhaleva,A.I.;Badre,S.;Dumas,C.;
Vasil’tsov, A. M.; Zorina, N. V.; Pansu, R. B. Tetrahedron 2005, 61, 2683.
(c) Sobenina, L. N.; Vasil’tsov, A. M.; Petrova, O. V.; Petrushenko, K. B.;
Ushakov, I. A.; Clavier, G.; Meallet-Renault, R.; Mikhaleva, A. I.;
Trofimov, B. A. Org. Lett. 2011, 13, 2524.
(7)(a) Lakshmi, V.; Rao, M. R.;Ravikanth, M. Org. Biomol. Chem. 2015,
13, 2501. (b) Rohand, T.; Baruah, M.; Qin, W.; Boens, N.; Dehaen, W.
Chem. Commun. 2006, 266. (c) Lakshmi, V.; Ravikanth, M. J. Org. Chem.
2011, 76,8466. (d)DuranSampedro, G.;Palao, E.;Agarrabeitia, A. R.;de
la Moya, S.; Boens, N.; Ortiz, M. J. RSC Adv. 2014, 4, 19210. (e) Wang, J.;
Zhou, X.; Yu, C.; Feng, Z.; Yu, Y.; Hao, E.; Wei, Y.; Mu, X.; Jiao, L. Org.
Lett. 2015, 17, 5360.
(8) (a) Verbelen, B.; Verbelen, B.; Leen, V.; Wang, L.; Boens, N.;
Dehaen, W. Chem. Commun. 2012, 48, 9129. (b)Leen, V.; Qin, W.;Yang,
W.; Cui, J.; Xu, C.; Tang, X.; Liu, W.; Robeyns, K.; Meervelt, L. V.;
Beljome, D.; Lazzaroni, R.; Tonnele, C.; Boens, N.; Dehaen, W. Chem. -
AsianJ. 2010, 5,2016. (c)Luo, L.;Wu,D.;Li,W.;Zhang, S.;Ma, Y.;Yuan,
S.;You, J. Org. Lett. 2014, 16, 6080. (d)Chong, H.;Lin, H.;Shen, M.;Liu,
C. Org. Lett. 2015, 17, 3198.
ASSOCIATED CONTENT
* Supporting Information
■
S
TheSupportingInformationisavailablefreeofchargeontheACS
Publications website at DOI: 10.1021/acs.orglett.5b03706.
Experimental details, tables, and additional spectra (PDF)
X-ray data for 1a, 1e, and 4a (CIF)
(9) (a) Verbelen, B.; Boodts, S.; Hofkens, J.; Boens, N.; Dehaen, W.
Angew. Chem., Int.Ed.2015,54,4612. (b)Verbelen, B.;Rezende,L.C. D.;
Boodts, S.; Jacobs, J.; Van Meervelt, L.; Hofkens, J.; Dehaen, W. Chem. -
Eur. J. 2015, 21, 12667.
(10) (a) Merritt, E. A.; Olofsson, B. Angew. Chem., Int. Ed. 2009, 48,
9052. (b) Guo, W.; Li, S.; Tang, L.; Li, M.; Wen, L.; Chen, C. Org. Lett.
2015, 17, 1232.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: jiao421@mail.ahnu.edu.cn.
Notes
The authors declare no competing financial interest.
(11)(a)Modha, S.G.;Greaney, M.F. J. Am. Chem. Soc. 2015, 137, 1416.
(b)Phipps, R.J.;Grimster, N. P.;Gaunt,M.J. J.Am. Chem. Soc.2008,130,
8172.(c)Zhu,Y.;Bauer, M.;Ploog,J.;Ackermann,L.Chem.-Eur.J.2014,
20, 13099. (d) Wagner, A. M.;Hickman, A. J.; Sanford, M. S. J. Am. Chem.
Soc. 2013, 135,15710. (e)Ciana, C.;Phipps, R.J.;Brandt, J. R.;Meyer, F.;
Gaunt,M.J.Angew.Chem.,Int.Ed.2011,50,458.(f)Storr,T.E.;Greaney,
M. F. Org. Lett. 2013, 15, 1410.
(12)(a)Jalalian,N.;Petersen,T.B.;Olofsson,B.Chem.-Eur.J.2012,18,
14140. (b) Petersen, T. B.; Khan, R.; Olofsson, B. Org. Lett. 2011, 13,
3462. (c)Jalalian, N.;Ishikawa,E.E.;Silva, L.F., Jr.;Olofsson,B. Org.Lett.
2011, 13, 1552. (d) Lindstedt, E.; Ghosh, R.;Olofsson, B. Org. Lett. 2013,
15, 6070.
(13)(a)Zhao,N.;Xuan,S.;Fronczek,F.R.;Smith,K.M.;Vicente,M.G.
H. J. Org. Chem. 2015, 80, 8377. (b) Lakshmi, V.; Ravikanth, M. Dalton
Trans. 2012, 41, 5903. (c) Jiao, L.;Pang, W.;Zhou, J.;Wu, Y.; Mu, X.; Bai,
G.; Hao, E. J. Org. Chem. 2011, 76, 9988. (d) Hayashi, Y.; Yamaguchi, S.;
Cha, W. Y.; Kim, D.; Shinokubo, H. Org. Lett. 2011, 13, 2992. (e) Yu, C.;
Jiao,L.;Yin,H.;Zhou,Z.;Pang,W.;Wu,Y.C.;Wang,Z.;Yang,G.;Hao,E.
Eur. J. Org. Chem. 2011, 5460. (f) Esnal, I.; Banuelos, J.; Arbeloa, I. L.;
Costela, A.;Garcia-Moreno, I.; Garzon, M.;Agarrbeitia, A. R.;Ortiz, M. J.
RSC Adv. 2013, 3, 1547.
ACKNOWLEDGMENTS
■
This work is supported by the National Nature Science
Foundation of China (21372011, 21402001, and 21472002)
and the Nature Science Foundation of Anhui Province
(1508085J07). The numerical calculations have been done on
the supercomputing system in the Supercomputing Center of
University of Science and Technology of China.
REFERENCES
■
(1) (a) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891. (b) Ulrich,
G.; Ziessel, R.; Harriman, A. Angew. Chem., Int. Ed. 2008, 47, 1184.
(c) Ziessel, R.; Ulrich, G.; Harriman, A. New J. Chem. 2007, 31, 496.
(d) Boens, N.; Leen, V.; Dehaen, W. Chem. Soc. Rev. 2012, 41, 1130.
(e) Lu, H.; Mack, J.; Yang, Y.; Shen, Z. Chem. Soc. Rev. 2014, 43, 4778.
(f) Ni, Y.; Wu, J. Org. Biomol. Chem. 2014, 12, 3774.
(2) (a) Kowada, T.; Maeda, H.; Kikuchi, K. Chem. Soc. Rev. 2015, 44,
4953. (b) Hiruta, Y.; Koiso, H.; Ozawa, H.; Sato, H.; Hamada, K.;
Yabushita, S.; Citterio, D.; Suzuki, K. Org. Lett. 2015, 17, 3022. (c) Isik,
M.; Guliyev, R.; Kolemen, S.; Altay, Y.; Senturk, T.; Akkaya, E. U. Org.
Lett. 2014, 16, 3260. (d) Erbas-Cakmak, S.; Akkaya, E. U. Org. Lett. 2014,
16, 2946.
(14)(a) Lubinkowski, J. J.;Arrieche, C. G.;McEwen, W. E. J. Org. Chem.
1980,45,2076.(b)Dektar,J.L.;Hacker,N.P.J.Org.Chem.1990,55,639.
(c) Wen, J.; Zhang, R.; Chen, S.; Zhang, J.; Yu, X. J. Org. Chem. 2012, 77,
(3) (a) Bessette, A.; Hanan, G. S. Chem. Soc. Rev. 2014, 43, 3342.
766. (d) Castro, S.;Fernan
F. Chem. Commun. 2012, 48, 9089.
́ ́
dez, J. J.;Vicente, R.;Fananas, F. J.;Rodríguez,
́ ̂
(b) Bura, T.; Leclerc, N.; Fall, S.; Leveque, P.; Heiser, T.; Retailleau, P.;
Rihn, S.; Mirloup, A.; Ziessel, R. J. Am. Chem. Soc. 2012, 134, 17404.
(c) Chen, J. J.; Conron, S. M.; Erwin, P.; Dimitriou, M.; McAlahney, K.;
Thompson, M. E. ACS Appl. Mater. Interfaces 2015, 7, 662.
D
DOI: 10.1021/acs.orglett.5b03706
Org. Lett. XXXX, XXX, XXX−XXX