Convergent Ditopic Receptors Enhance Anion Binding upon Alkali Metal Complexation for Catalyzing the Ritter Reaction

Article abstract of DOI:10.1021/acs.orglett.8b03778

A supramolecular approach to catalyzing the Ritter reaction by utilizing enhanced anion-binding affinity in the presence of alkali metal cations was developed with ditopic hydrogen-bonded amide macrocycles. With prebound cations in the macrocycle, particu

Full text of DOI:10.1021/acs.orglett.8b03778

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Convergent Ditopic Receptors Enhance Anion Binding upon Alkali
Metal Complexation for Catalyzing the Ritter Reaction
Kang Kang,† Jessica A. Lohrman,‡ Sangaraiah Nagarajan,† Lixi Chen,† Pengchi Deng,† Xin Shen,†
Kuirong Fu,† Wen Feng,*,† Darren W. Johnson,*,‡ and Lihua Yuan*,†
†Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology,
College of Chemistry, Analytical & Testing Center, Sichuan University, Chengdu 610064, China
‡Department of Chemistry & Biochemistry and the Materials Science Institute, University of Oregon, Eugene, Oregon 97403-1253,
United States
S
* Supporting Information
ABSTRACT: A supramolecular approach to catalyzing the Ritter reaction by
utilizing enhanced anion-binding affinity in the presence of alkali metal cations was
developed with ditopic hydrogen-bonded amide macrocycles. With prebound
cations in the macrocycle, particularly Li+ ion, their metal complexes exhibit
greatly enhanced catalytic activities. The catalysis is switchable by removal or
addition of the bound cation. The method described in this work may be
generalized for use in other anion-triggered organic reactions involving
heteroditopic receptors capable of ion pairing.
he past decade has witnessed a growing wealth of ditopic
Treceptors that are capable of cooperatively binding pairs of
cations and anions.1 Compared to a monotopic molecular
receptor2 that only recognizes a single ion, these receptors show
enhanced binding affinity and selectivity, leading to interesting
applications which include salt solubilization,3 extraction,4 ion-
sensing, and transmembrane ion transport.5 So far, ion-pair
binding has been explored in a variety of scaffolds including
crown ethers,6 calix[4]pyrroles,7 and urea derivatives.8 In
particular, hosts that utilize convergent binding sites have
Figure 1. Molecular structures of hydrogen-bonded receptors with
shown a significant increase in anion affinity and selectivity in
the presence of alkali metal cations.9 While direct complexation
of inorganic salts requires both ionic species to be bound to two
specific sites, a cation-enhanced anion binding process involves
addition of a metal cation first, followed by introduction of an
external anionic guest to the core of the receptor system. This
would be useful in catalyzing a reaction when the mechanism
calls for anion sequestration. Despite many reports on research
into enhanced anion binding in the presence of alkali metal ions
with ditopic receptors,10 none of these have been developed for
catalytic reactions.
Recently, anion-binding receptors have attracted particular
interest in supramolecular catalysis.11 Catalysts that require
anion sequestration generally employ hydrogen-bonding
interactions based on strongly polarized N−H,12 O−H,13 aryl
C−H14 and halogen bonds.15 Our previous work with
hydrogen-bonded (H-bonded) amide macrocycles16 (Figure
1) showed that convergent heteroditopic cyclo[6]aramides17
were able to coordinate organic ion pairs. This is ascribed to a
protons labeled and their cartoon representation and alkali metal ions/
anions involved in the catalytic reaction.
convergent binding site composed of two amide N−Hs and an
aryl C−H serving as H-bond donors for anions and four amide
carbonyl oxygens for cations. However, use of H-bonded
aromatic amide macrocycles18 for binding anionic guests to
achieve catalytic reactions has reamined unknown.
Herein, we present a supramolecular strategy for catalysis of
the Ritter reaction by using convergent H-bonded amide
macrocycles as receptors with prebound alkali metal to enhance
anion affinity. Importantly, the catalytic process was found to be
switchable in an on-and-off manner triggered by external
addition of inorganic salts. To this end, two new ditopic
receptors (1a and 1b), bearing −NO2 and −OMe groups with
contrasting electronic properties, were synthesized (Figures
Received: November 26, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b03778
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 1. Association Constants Ka (M−1) of Complexes in
CDCl3/CD3CN (1:1, v/v) at 298 K
S1−S9). The anion-binding effect with the presence of alkali
metal ions was probed first, followed by employing the cation
complex of the heteroditopic receptors as anion-binding
catalysts for promoting the Ritter reaction.
receptor
Cl−
Br−
I−
Anion affinity for halide guests (Cl−, Br−, and I−) was initially
determined (Figure 2) in the absence of alkali metal cations via
1H NMR spectroscopy studies in a 1:1 solution of CDCl3 and
CD3CN using tetrabutylammonium (TBA) salts, since TBA is
too large to fit in the ditopic receptor binding pocket (Figure
S11). Downfield shifting of amide NH (Hj) and aromatic ArH
resonances (Hk) in receptor 1a was observed only for Cl−, while
H-bond donor resonances remained unmoved upon addition of
Br− and I−, indicating receptor selectivity toward Cl−. As
expected, receptor 1b containing the electron-donating group
(OMe) shows a relatively smaller chemical shift upon anion
addition owing to the decreased acidity of amide protons
(Figure S12). The receptors were also assessed for alkali metal
1a
110
2300
4000
4900
a
a
b
b
1a·Li+
1a·Na+
1a·K+
1100, 55000
4200
3800
9800
a
a
a
Ka < 10 M−1 and could not be accurately determined.
Stoichiometry was 2:1.
b
Ka for all of the halide anions in comparison to the metal-free
system. The enhanced affinity afforded by the presence of Li+
allowed for an accurate determination of the Ka of Cl− (Ka =
2300 M−1), Br− (K1 = 1100 M−1, K2 = 55000 M−1), and I− (Ka =
9800 M−1), which are otherwise not observed in the absence of
Li+ salt. A 1:1 binding stoichiometry for Cl− and Br− in the
presence of Na+ and K+ was derived from the 1H NMR titration
curves for 1a and 1b (Figures S24−S53). Furthermore, job plot
experiments suggested a 2:1 stoichiometry between the complex
of 1a·Li+ and Br− (Figure S32).
ions Li+, Na+, and K+ in the form of their perchlorate (ClO4 )
−
−
and hexafluorophosphate (PF6 ) salts (Figures S10 and S15−
S17). The response to either anions or cations indicates site-
specific binding by these convergent heteroditopic receptors.
Subsequently, anion-binding properties for halide guests were
evaluated (Figure 2) in the presence of alkali metal cations.
Addition of Br− to a solution of 1a·Li+ in a 1:1 solution of CDCl3
and CD3CN leads to 0.66 and 0.61 ppm downfield shifts of Hj
and Hk (Figure 2). Tests of 1b·Li+ with Br− followed the same
trend (Figure S14). Typically, shifting observed in the presence
of Li+ increases by over 6-fold compared to the shifting in the
absence of these metal ions (Figure S13). This indicates that
prebound metal cations can enhance the complexation of anions
by these ditopic receptors. Recently, the Johnson and Haley
groups also revealed a similar phenomenon with a phosphine
oxide based ditopic receptor.19
While significant increases in Ka for Cl− and Br− persisted in
the presence of Na+ and K+ cations, I− remained unbound. The
inability to effectively bind I− is attributed to the confined cavity
restricting the size of the halide guest after the coordination of
larger metal ions. With no metal ion present, 1a was unable to
engulf I−; however, after the addition of smaller-sized Li+, I− was
strongly bound with a Ka as high as 9800 M−1. Therefore, I−
could only be accommodated alongside a smaller cation (Li+)
where sufficient space was still available for the larger anionic
guest. These findings were echoed by a similar ion-size trend that
was observed for 1b (Table S2).The enhanced anion affinity is
attributed to cooperative action from hydrogen bonding of
amide NH with the anion and electrostatic attraction from the
metal cation within the cavity, the later of which is corroborated
by the loss of binding of Br− and I− with the receptor 1a alone,
and the inability of 1b to bind any halides in the absence of alkali
metals. The affinity increases between 1a and 1a·cation
complexes are further supported by the results from the Gibbs
free energies (ΔΔG) (Table S2).
The strong halide binding exhibited by macrocycles 1a and 1b
in the presence of alkali metals makes them attractive as
supramolecular catalysts. The catalytic potential of the hosts was
investigated by using the Ritter reaction of bromodiphenyl-
methane (2a) and acetonitrile as a benchmark reaction. The
receptors are expected to promote cleavage of the carbon−
bromide bond, wherein the Ritter product, benzhydryl
acetamide (2b), is formed. Reactions were run in the presence
of stoichiometric amounts of catalyst (20 mol %) at room
temperature for 5 days (Figures S58−S60). The resulting yields
of benzhydryl acetamide are reported in Table 2.
Figure 2. Partial 1H NMR spectra (400 MHz, CDCl3/CD3CN, v/v =
1/1, 298 K) of receptor 1a and 1a·Li with 2 equiv of halide ions. ( ) =
Hj, (Δ) = Hk.
+
●
A control reaction composed solely of 2a in a 1:1 solution of
CH2Cl2 and CH3CN was performed and failed to effectively
afford Ritter product 2b in the absence of catalyst (Table 2, entry
1). The addition of metal-free 1a also failed to catalyze the
reaction (Table 2, entry 2) due to its weak affinity for Br−.
Subsequently, a series of experiments involving the alkali metal
(Li+, Na+, and K+) complexes of 1a and 1b as the catalysts were
carried out under the same conditions as the control
experiments (Table 2, entries 3−12). In the presence of 1
equiv of alkali cations, the reaction proceeded to a significant
extent as indicated by the yields of 42% (1a·Li+), 18% (1a·Na+),
and 16% (1a·K+), with Li+ exhibiting the highest yield (Table 2,
To quantify the anion-binding ability of receptors 1a and 1b
in the absence or presence of alkali metal cations, H NMR
1
spectroscopy titration experiments were performed in a 1:1
solution of CDCl3 and CD3CN and the downfield shifts of the
amide resonances (Hj) were tracked after addition of TBA salts
of the halides. The binding constants (Table 1 and Table S2)
were determined by fitting to a 1:1 binding model for all
experiments except for 1a·Li+ and 1b·Li+ binding with Br−,
which was fit to a 2:1 binding model20 (Figures S18−S55).
The anions affinities for 1a·Li+ were determined using lithium
perchlorate as a Li+ source and yielded a noticeable increase in
B
DOI: 10.1021/acs.orglett.8b03778
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 2. Investigation of the Anion-Binding-Catalyzed Ritter
Reaction with Various Potential Catalysts
Scheme 1. Proposed Catalytic Cycle and Switchable
Catalyzed Reaction
a
c
entry
catalyst
yield (%)
1
2
3
4
5
6
7
8
b
1a
1a·Li+
1a·Na+
1a·K+
<5
<5
42
18
16
<5
64
57
22
36
18
20
d
1a + CF3CO2H (20%)
1a·(10 equiv of Li+)
d
1a·Li+ + CF3CO2H (20%)
9
1b·Li+
10
11
12
1b·(10 equiv of Li+)
1b·Na+
1b·K+
a
Reaction conditions: 20 μmol of 2a and 4 μmol of catalyst (20 mol
%) in 2.0 mL of 1:1 solution of CH2Cl2 and CH3CN at room
b
c
temperature. In the absence of any macrocycle or catalyst. Yields
d
1
determined after 5 days by H NMR. 20 mol % of CF3CO2H was
added.
as the catalyst (Table 2, entry 8) compared to the case with 1a
alone (Table 2, entry 6) where only the starting material is
recovered. This suggests that the presence of proton source
favors the departure of bromide trapped in the macrocyclic
complex to generate the catalyst again for use in the next
catalytic cycle.
entry 3). Furthermore, increasing the amount of Li+ to 10 equiv
led to an even higher yield of 64% (Table 2, entry 7). Excess Li+
can increase the amount of 1a·Li+ owing to the equilibrium
between the receptor and Li+. Low solubility of the Na+ and K+
salts prevented any catalytic reactions at higher concentrations
of the cations. These results indicate that 1a can effectively
catalyze the reaction in the presence of Li+ compared to other
metal ions. Under the same conditions, the contrasted receptor
1b catalyzed the reaction less effectively (Table 2, entries 9−12).
Obviously, the difference in catalytic activity between 1a and 1b
can be ascribed to the electronic effect of substituents in the
macrocycles: an electron-withdrawing group (X = NO2)
enhances the acidity of NH protons, which in turn, assists
binding of the Br−. In the presence of Na+ and K+ salts, they give
very similar results (Table 2, entries 11 and 12), possibly as a
result of relatively loose binding of the anion compared to the
use of Li+ (Table 1).
A mechanistic pathway would be the catalyst-assisted cleavage
of the carbon−bromide bond of 2a followed by the rapid attack
of acetonitrile (Scheme 1a). To gain a better understanding of
the in situ capture of the Br− by the 1a·Li+ complex in the course
of Ritter reaction, we performed NMR titration studies of 1a·Li+
and 1b·Li+ with the substrate 2a in CDCl3/CD3CN (1/1)
(Figures S56 and S57). The amide protons Hj were found to
shift downfield upon addition of 2a. The noticeable change in
chemical shifts is a consequence of binding of the Br− as the
reaction progresses. This strongly supports the proposition in
the first step that 1a·Li+ activates the brominated substrate 2a via
hydrogen bonding to promote the formation of carbocation.
This is followed by nucleophilic attack by a molecule of
acetonitrile to generate the nitrilium cation.21 To evidence the
possibility in the next step that the adduct formed by addition of
a molecule of water from the wet solvent acts as a proton source
to facilitate removal of bound Br− from the cavity, CF3CO2H
(20 mol %) was added to the reaction system. Indeed, a
significant increase in yield up to 57% was observed with 1a·Li+
The reversible switching of the catalytic process between ON
and OFF was also tested (Scheme 1b). Upon addition of excess
−
HSO4 (10 equiv) as its tetrabutylammonium salt to the
reaction system, no conversion to product 2b was observed. The
Ritter reaction was turned “off” as a result of precipitation of
LiHSO4 (Figure S61). Increasing the concentration of Li+ by in
situ adding its salt switched “on” the reaction, resulting in a yield
of 49% comparable to the case with 1a·Li+ as the catalyst (Table
2, entry 3). This result proves possible to control the progress of
the Ritter reaction by removal or addition of Li+ cation.
In conclusion, we have demonstrated that convergent ditopic
H-bonded amide macrocycles can effectively enhance the
binding affinity for anions in the presence of alkali metal
cations. In particular, a greater increase in the binding of Br− is
observed in the presence of lithium ion. With this as a starting
point, a practical approach to catalyzing the Ritter reaction by
exploiting enhanced anion-binding affinity was developed. The
catalytic process can be switched in an on-and-off fashion. Our
work provides an alternative way to catalyze anion-promoted
catalytic reactions by utilizing cation-dependent anion affinity
effects, which may find applications in other anion-promoted
reaction systems using various heteroditopic receptors.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.8b03778.
Experimental procedures, characterization of compounds
1a and 1b, and additional NMR, IR, and ESI-MS spectra
(PDF)
C
DOI: 10.1021/acs.orglett.8b03778
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(8) (a) Nabeshima, T.; Saiki, T.; Iwabuchi, J.; Akine, S. J. Am. Chem.
AUTHOR INFORMATION
■
́
Soc. 2005, 127, 5507. (b) Karbarz, M.; Romanski, J. Inorg. Chem. 2016,
Corresponding Authors
55, 3616.
(9) (a) Picot, S. C.; Mullaney, B. R.; Beer, P. D. Chem. - Eur. J. 2012,
18, 6230. (b) Mahoney, J. M.; Beatty, A. M.; Smith, B. D. Inorg. Chem.
2004, 43, 7617.
*E-mail: wfeng9510@scu.edu.cn.
*E-mail: dwj@uoregon.edu.
*E-mail: lhyuan@scu.edu.cn.
(10) For selected articles about ditopic receptors, see: (a) Akhuli, B.;
ORCID
̈ ̈
Ghosh, P. Chem. Commun. 2015, 51, 16514. (b) Makela, T.; Kalenius,
E.; Rissanen, K. Inorg. Chem. 2015, 54, 9154. (c) Lee, J. H.; Lee, J. H.;
Choi, Y. R.; Kang, P.; Choi, M.-G.; Jeong, K.-S. J. Org. Chem. 2014, 79,
6403. (d) Tumcharern, G.; Tuntulani, T.; Coles, S. J.; Hursthouse, M.
B.; Kilburn, J. D. Org. Lett. 2003, 5, 4971. (e) Scheerder, J.; van
Duynhoven, J. P. M.; Engbersen, J. F. J.; Reinhoudt, D. N. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1090.
Darren W. Johnson: 0000-0001-5967-5115
Lihua Yuan: 0000-0003-0578-4214
Notes
The authors declare no competing financial interest.
(11) (a) Eichstaedt, K.; Jaramillo-Garcia, J.; Leigh, D. A.; Marcos, V.;
Pisano, S.; Singleton, T. A. J. Am. Chem. Soc. 2017, 139, 9376.
̃
(b) Fischer, T.; Duong, Q.-N.; Mancheno, O. G. Chem. - Eur. J. 2017,
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (21572143), Post-Doctoral Research and
Development Foundation of Sichuan University
(2017SCU12001), and Open Project of State Key Laboratory
of Supramolecular Structure and Materials (SKLSSM201831).
The Analytical & Testing Center of Sichuan University is
acknowledged for NMR analysis. Research reported in this
publication was supported by the National Institute of General
Medical Sciences of the National Institutes of Health under
Award No. R01-GM087398 (D.W.J., J.A.L.). This work was also
supported by the Bradshaw and Holzapfel Research Professor-
ship in Transformational Science and Mathematics (D.W.J.).
23, 5983. (c) Marcos, V.; Stephens, A. J.; Jaramillo-Garcia, J.;
Nussbaumer, A. L.; Woltering, S. L.; Valero, A.; Lemonnier, J.-F.;
Vitorica-Yrezabal, I. J.; Leigh, D. A. Science 2016, 352, 1555. (d) Kniep,
F.; Rout, L.; Walter, S. M.; Bensch, H. K. V.; Jungbauer, S. H.;
Herdtweck, E.; Huber, S. M. Chem. Commun. 2012, 48, 9299. (e) Zhao,
H.; Shen, J.; Guo, J.; Ye, R.; Zeng, H. Chem. Commun. 2013, 49, 2323.
(12) (a) Ford, D. D.; Lehnherr, D.; Kennedy, C. R.; Jacobsen, E. N. J.
Am. Chem. Soc. 2016, 138, 7860. (b) Zhao, C.; Sojdak, C. A.; Myint, W.;
Seidel, D. J. Am. Chem. Soc. 2017, 139, 10224. (c) Borovika, A.; Tang,
P.-I.; Klapman, S.; Nagorny, P. Angew. Chem., Int. Ed. 2013, 52, 13424.
(13) (a) Beletskiy, E. V.; Schmidt, J.; Wang, X.-B.; Kass, S. R. J. Am.
Chem. Soc. 2012, 134, 18534. (b) Schafer, A. G.; Wieting, J. M.; Fisher,
T. J.; Mattson, A. E. Angew. Chem. 2013, 125, 11531.
(14) (a) Zurro, M.; Asmus, S.; Beckendorf, S.; Mu
̈
ck-Lichtenfeld, C.;
o,
Mancheno, O. G. J. Am. Chem. Soc. 2014, 136, 13999. (b) Manchen
̃
̃
REFERENCES
O. G.; Asmus, S.; Zurro, M.; Fischer, T. Angew. Chem., Int. Ed. 2015, 54,
■
8823.
(1) (a) Kim, S. K.; Sessler, J. L. Chem. Soc. Rev. 2010, 39, 3784.
(b) Naseer, M. M.; Jurkschat, K. Chem. Commun. 2017, 53, 8122.
(c) Gale, P. A. Coord. Chem. Rev. 2003, 240, 191. (d) Maity, K.; Panda,
D. K.; Gallup, R. J.; Choudhury, C. K.; Saha, S. Org. Lett. 2018, 20, 962.
(2) (a) Shang, J.; Zhao, W.; Li, X.; Wang, Y.; Jiang, H. Chem. Commun.
2016, 52, 4505. (b) Liu, H. B.; Zhang, Q.; Wang, M. X. Angew. Chem.,
Int. Ed. 2018, 57, 6536. (c) Zhong, Z.; Li, X.; Zhao, Y. J. Am. Chem. Soc.
2011, 133, 8862. (d) Jin, C.; Zhang, M.; Wu, L.; Guan, Y.; Pan, Y.; Jiang,
J.; Lin, C.; Wang, L. Chem. Commun. 2013, 49, 2025. (e) Jiang, B.;
Wang, W.; Zhang, Y.; Lu, Y.; Zhang, C.-W.; Yin, G.-Q.; Zhao, X.-L.; Xu,
L.; Tan, H.; Li, X.; Jin, G.-X.; Yang, H.-B. Angew. Chem. 2017, 129,
14630. (f) Zhu, H.; Shi, B.; Chen, X.; Wei, P.; Xia, D.; Mondal, J. H.;
Huang, F. Org. Lett. 2016, 18, 5054. (g) Zhou, Y.; Chen, Y.; Zhu, P.-P.;
Si, W.; Hou, J.-L.; Liu, Y. Chem. Commun. 2017, 53, 3681. (h) Du, J.;
Kang, K.; Hu, J. C.; Mao, L. J.; Yuan, L. H.; Feng, W. Chin. J. Chem.
2016, 34, 866. (i) Li, M.; Lu, H.-Y.; Liu, R.-L.; Chen, J.-D.; Chen, C.-F.
J. Org. Chem. 2012, 77, 3670.
(15) Jungbauer, S. H.; Huber, S. M. J. Am. Chem. Soc. 2015, 137,
12110.
(16) (a) Hu, J. C.; Chen, L.; Ren, Y.; Deng, P. C.; Li, X. W.; Wang, Y.
J.; Jia, Y. M.; Luo, J.; Yang, X. S.; Feng, W.; Yuan, L. H. Org. Lett. 2013,
15, 4670. (b) He, Y. Z.; Xu, M.; Gao, R. Z.; Li, X. W.; Li, F. X.; Wu, X.
D.; Xu, D. G.; Zeng, H.; Yuan, L. H. Angew. Chem., Int. Ed. 2014, 53,
11834. (c) Li, X. W.; Li, B.; Chen, L.; Hu, J. C.; Wen, C. D.; Zheng, Q.
D.; Wu, L. X.; Zeng, H.; Gong, B.; Yuan, L. H. Angew. Chem., Int. Ed.
2015, 54, 11147. (d) Chen, L.; Peng, Z. Y.; Liu, S.; Li, X. W.; Chen, R.
Z.; Ren, Y.; Feng, W.; Yuan, L. H. Org. Lett. 2015, 17, 5950. (e) Mao, L.
J.; Pan, W.; Fu, Y. H.; Chen, L.; Xu, M.; Ren, Y.; Feng, W.; Yuan, L. H.
Org. Lett. 2017, 19, 18. (f) Li, X. W.; Yuan, X. Y.; Deng, P. C.; Chen, L.
X.; Ren, Y.; Wang, C. Y.; Wu, L. X.; Feng, W.; Gong, B.; Yuan, L. H.
Chem. Sci. 2017, 8, 2091. (g) Pan, W.; Mao, L. J.; Shi, M. S.; Fu, Y. H.;
Jiang, X. M.; Feng, W.; He, Y. Z.; Xu, D. G.; Yuan, L. H. New J. Chem.
2018, 42, 3857.
(17) (a) Hu, J. C.; Chen, L.; Shen, J.; Luo, J.; Deng, P. C.; Ren, Y.;
Zeng, H.; Feng, W.; Yuan, L. H. Chem. Commun. 2014, 50, 8024.
(b) Kang, K.; Huang, W.; Fu, Y. H.; Chen, L.; Hu, J. C.; Ren, Y.; Feng,
W.; Yuan, L. H. Supramol. Chem. 2017, 29, 730.
(18) (a) Adams, H.; Carver, F. J.; Hunter, C. A.; Osborne, N. J. Chem.
Commun. 1996, 2529. (b) Shirude, P. S.; Gillies, E. R.; Ladame, S.;
Godde, F.; Shinya, K.; Huc, I.; Balasubramanian, S. J. Am. Chem. Soc.
2007, 129, 11890. (c) Gong, B. Acc. Chem. Res. 2008, 41, 1376.
(d) Zhang, D.-W.; Zhao, X.; Hou, J.-L.; Li, Z.-T. Chem. Rev. 2012, 112,
5271. (e) Ong, W. Q.; Zeng, H. J. Inclusion Phenom. Mol. Recognit.
Chem. 2013, 76, 1.
(3) (a) Pelizzi, N.; Casnati, A.; Friggeri, A.; Ungaro, R. J. Chem. Soc.,
Perkin Trans. 2 1998, 1307. (b) Sun, Z. H.; Pan, F. F.; Triyanti;
Albrecht, M.; Raabe, G. Eur. J. Org. Chem. 2013, 2013, 7922.
(4) (a) Zakrzewski, M.; Kwietniewska, N.; Walczak, W.; Piaţ ek, P.
Chem. Commun. 2018, 54, 7018. (b) He, Q.; Williams, N. J.; Oh, J. H.;
Lynch, V. M.; Kim, S. K.; Moyer, B. A.; Sessler, J. L. Angew. Chem. 2018,
130, 12100.
(5) (a) Ren, C.; Zeng, F.; Shen, J.; Chen, F.; Roy, A.; Zhou, S.; Ren,
H.; Zeng, H. J. Am. Chem. Soc. 2018, 140, 8817. (b) Gong, H. Y.;
Rambo, B. M.; Karnas, E.; Lynch, V. M.; Keller, K. M.; Sessler, J. L. J.
Am. Chem. Soc. 2011, 133, 1526. (c) Xin, P.; Zhang, L.; Su, P.; Hou, J.-
L.; Li, Z.-T Chem. Commun. 2015, 51, 4819.
(6) (a) Qiao, B.; Sengupta, A.; Liu, Y.; McDonald, K. P.; Pink, M.;
Anderson, J. R.; Raghavachari, K.; Flood, A. H. J. Am. Chem. Soc. 2015,
137, 9746. (b) Miyaji, H.; Kim, D.-S.; Chang, B.-Y.; Park, E.; Park, S.-
M.; Ahn, K. H. Chem. Commun. 2008, 6, 753.
(19) (a) Gavette, J. V.; Lara, J.; Berryman, O. B.; Zakharov, L. N.;
Haley, M. M.; Johnson, D. W. Chem. Commun. 2011, 47, 7653.
(b) Gavette, J. V.; Lara, J.; Reling, L. L.; Haley, M. M.; Johnson, D. W.
Chem. Sci. 2013, 4, 585.
(20) Thordarson, P. Chem. Soc. Rev. 2011, 40, 1305.
(21) Sanz, R.; Martínez, A.; Guilarte, V.; Alvarez-Gutierrez, J. M.;
Rodríguez, F. Eur. J. Org. Chem. 2007, 2007, 4642.
́
́
(7) (a) Ellis, R. J.; Reinhart, B.; Williams, N. J.; Moyer, B. A.;
Bryantsev, V. S. Chem. Commun. 2017, 53, 5610. (b) Romero, J. R.;
Aragay, G.; Ballester, P. Chem. Sci. 2017, 8, 491.
D
DOI: 10.1021/acs.orglett.8b03778
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