Mild Friedel–Crafts Reactions inside a Hexameric Resorcinarene Capsule: C?Cl Bond Activation through Hydrogen Bonding to Bridging Water Molecules

Article abstract of DOI:10.1002/anie.201801642

A novel catalytic feature of a hexameric resorcinarene capsule is highlighted. The self-assembled cage was exploited to promote the Friedel–Crafts benzylation of several arenes and heteroarenes with benzyl chloride under mild conditions. Calculations showed that there are catalytically relevant hydrogen-bonding interactions between the bridging water molecules of the capsule and benzyl chloride, which is fundamental for the activation of the C?Cl bond. The capsule controls the reaction outcome. Inside the inner cavity of the capsule, N-methylpyrrole is preferentially benzylated in the unusual β-position while mesitylene reacts faster than 1,3-dimethoxybenzene despite the greater π-nucleophilicity of the latter compound.

Full text of DOI:10.1002/anie.201801642

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Supramolecularly-Driven Mild Friedel-Crafts Reaction Inside the
Hexameric Resorcinarene Capsule: C-Cl Bond Activation by H-
Bonding with the Bridged Water Molecules
Authors: Carmine Gaeta, Pellegrino La Manna, Carmen Talotta,
Giuseppe Floresta, Margherita De Rosa, Annunziata Soriente,
Antonio Rescifina, and Placido Neri
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201801642
Angew. Chem. 10.1002/ange.201801642
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10.1002/anie.201801642
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Supramolecularly-Driven Mild Friedel-Crafts Reaction Inside the
Hexameric Resorcinarene Capsule: C–Cl Bond Activation by H-
Bonding with the Bridged Water Molecules
Pellegrino La Manna,[a] Carmen Talotta,[a] Giuseppe Floresta,[b,c] Margherita De Rosa,*,[a] Annunziata
Soriente,[a] Antonio Rescifina,*,[c] Carmine Gaeta,*,[a] and Placido Neri [a]
Dedicated to Prof. Jerry L. Atwood on the occasion of his 75th birthday
Abstract: A novel catalytical feature of the hexameric resorcinarene
capsule (C) is here highlighted. The self-assembled cage C has been
exploited to promote a mild Friedel-Crafts benzylation of several
arenes and heteroarenes. In silico studies show the existence of a
catalytically relevant H-bonding interaction between the bridged water
molecules of the capsule and benzyl chloride, which is fundamental
for the activation of the C–Cl bond. A supramolecular control of the
capsule on the reaction outcome is evidenced. Inside the inner space
of the capsule, N-methylpyrrole is preferentially benzylated in the
unusual -position, while mesitylene reacts faster than 1,3-
dimethoxybenzene, despite the greater -nucleophilicity of this latter.
The hexameric capsule (1)6•8H2O (C)[4] which is obtained by
self-assembly of six resorcinarene 1 units and eight water
molecules[4a] (Figure 1), has been largely exploited as
nanoreactor,[5] thanks to its capacity to host selectively the
substrates and to accelerate the organic reactions with excellent
chemo-, regio-, and stereoselectivity.[6] Examination of the
literature data revealed that nanoreactor
C shows some
catalytically relevant features of interest for the catalysis of
organic reactions. Inside the hexameric capsule have been
accelerated a variety of organic reactions involving cationic
intermediates and transition states thanks to their stabilization
induced by the -electron-rich aromatic cavity of C.[7] Moreover,
nanoreactor C shows a remarkable Brønsted acidity (pKa = 5.9
measured in water-saturated CDCl3 and relative to the reported
aniline pKa-value in water) which has been exploited for the
catalysis of chemical reactions.[8]
-Nucleophiles represent useful building blocks in organic
synthesis thanks to their use in carbon-carbon bond-forming
reactions with electrophiles.[1] Among them, the Friedel-Crafts
(FC) alkylation of arene and heteroarene with aliphatic and
benzylic groups is particularly investigated.[2] Traditionally, this
reaction is promoted by Lewis acids,[2] but recently, much
attention has been focused on environmentally-oriented catalytic
strategies based on metal free approaches.[3] Thus, Paquin and
coworkers,[3a] reported a FC benzylation of arenes using benzyl
fluoride in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as solvent.
Their results evidenced a mechanism involving the activation of
the C–F bond through an H-bonding interaction between the
fluorine as H-bond acceptor and HFIP as H-bond donor.
Analogously, Mayr and coworkers showed that the FC reaction
between 4-methoxybenzyl halides and arenes occurs in 2,2,2-
trifluoroethanol.[3b] Also, in this case, the authors remark the role
of the hydroxylic solvent (CF3CH2OH) in the activation of the C–X
bond.
Figure 1. Chemical drawing of C-undecylresorcin[4]arene 1 (left) and a model
of the hexameric capsule (1)6•(H2O)8 (C) (right); undecyl chains and H-atoms
have been removed for clarity, while bridged H2O molecules are represented as
CPK model.
[a]
P. La Manna, Dr. C. Talotta, Dr. M. De Rosa, Prof. A. Soriente, Prof.
C. Gaeta, Prof. Dr. P. Neri
Dipartimento di Chimica e Biologia “A. Zambelli”
Università di Salerno
Via Giovanni Paolo II, 132, I-84084, Fisciano (Salerno), Italy
E-mail: neri@unisa.it
G. Floresta
Dipartimento di Scienze Chimiche
Università di Catania
Viale A. Doria, 6, 95125, Catania, Italy
Prof. A. Rescifina
Dipartimento di Scienze del Farmaco
Università di Catania
Interestingly, very recently, we have shown the existence of
catalytically relevant H-bonding interactions between the bridged
water molecule (in CPK model in Figure 1) in C and substrates
hosted inside the cavity.[6] On the basis of this considerations, and
in accordance with the results previously reported by Paquin,3a we
envisioned that the H-bond donor abilities of the bridged water
molecules in C[6] could play a role in the catalysis of FC alkylation
of -nucleophiles through the H-bonding activation of the C–X
bond.
[b]
[c]
Viale Andrea Doria, 6, 95125, Catania, Italy
Supporting information for this article is given via a link at the end of
the document.
Consequently, as a part of our ongoing project aimed at the
exploration of the large possibilities offered by catalysis into
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10.1002/anie.201801642
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COMMUNICATION
confined environments,[6] with particular regard to the C–C bond
forming reactions,[9] we studied the FC benzylation of aromatic
and heteroaromatic compounds with benzyl halides (Scheme 1)
inside the hexameric capsule (Figure 1), and we wish to report
here the results of our studies.
capsule C is able to drive the regiochemistry of the FC benzylation
of N-methylpyrrole in Scheme 1 towards an unconventional route.
Of course, this represents an interesting example of
supramolecular control of a reaction outcome.[12]
Scheme 1. Friedel-Crafts reaction between N-methylpyrrole and benzyl halides
promoted by C.
Initially, we investigated the reaction between N-methylpyrrole
2 and benzyl chloride 3a in the presence of C (26%) (Scheme 1),
using water-saturated[5] CDCl3 as the solvent.[5] When the reaction
mixture was stirred at 30 °C for 16 h the products 4 were obtained
in 20% of total yield. Surprisingly the -alkylated product -4 was
favored with respect to the -regioisomer -4 with a 90/10 ratio
(Table 1, entry 2). This is an intriguing result since the benzylation
at the 2-position of N-methylpyrrole,[10] under FC conditions, is
usually the favored one.[11]
Table 1. Friedel-Crafts reaction between N-methylpyrrole 2 and benzyl halides
promoted by hexameric resorcinarene capsule C.
Scheme 2. The mechanism proposed for the preferential formation of -4 inside
the hexameric capsule C, as calculated through in silico studies (SI) of the FC
reaction between 2 and 3a inside the model capsule CR having shorter feet.
Inset: H-bonding interaction between the chlorine atom of 3a and a bridged
water molecule of C in the hetero-binary complex [2+3a]@CR. Only the atoms
of the ONIOM high layer have been represented; the capsule has been
schematized in blue. The chlorine atom is engaged in a hydrogen bond with a
water molecule. The distances are given in Å. Carried out with CYLview.
Entry[a] T (°C)
X
Equiv. of
Capsule
amount (mol%)
Yield
(%)[b]
Ratio
2
-4/-4[c]
1
30
30
30
50
50
50
50
Cl
Cl
Cl
Cl
Br
F
1.5
1.5
1.5
1.5
1.5
1.5
1.5
0
0[d]
20
0
—
90/10
—
2
26
26
52
52
52
52
3[e]
4[f]
5[f]
6[f]
7[f]
81
72
75
—
94/6
91/9
85/15
—
When the reaction in Scheme 1 was performed in the absence
of C, regardless of the kind of benzyl halide exploited, no hint of
conversion of 2 and 3a into 4 (Table 1, entry 1) was observed by
NMR spectroscopy. These data strongly suggested that the
reaction in Scheme 1 occurs inside C. This was confirmed by the
I
–
finding that in the presence of (Et)4N+BF4 (0.76 M), as a
competitive guest,[13] no conversion of 2 and 3a into 4 was
[a]
Reaction conditions: 2 (0.22 M), 3 (0.15 M), C (0.076 M) in 1.1 mL of water-
saturated CDCl3, 16 h. [b] Isolated yield. [c] Determined by 1H NMR analysis (SI). [d]
Analogous result was observed when the reaction was performed at 50 °C. [e] The
reaction was performed in the presence of Et4N+BF4– (0.76 M). [f]Only starting
materials were recovered when the reaction was performed in the absence of
capsule C.
observed (Table 1, entry 3). In addition, a 1H NMR spectrum (SI,
–
Figure S2) of the reaction mixture in the presence of (Et)4N+BF4 ,
showed the presence of shielded signals at negative values of
chemical shifts attributable to tetraethyl cation inside the cavity of
C. Furthermore, no hints of products 4 were detected when the
reaction in Scheme 1 was performed in the presence of hydrogen-
bond competitor solvents (e.g., DMSO).
However, some examples have been reported in which a 1:1
mixture of / regioisomers was obtained.[11c, 11e] Consequently,
on the basis of this results we can conclude that the hexameric
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As previously discussed C shows a strong affinity for cationic
guests,[7] consequently, a question arises whether it is able or not
to accommodate -electron-rich aromatic nucleophiles. Detailed
NMR studies (see EXSY, COSY, HSQC, and DOSY experiments
in SI) clearly indicated that both N-methylpyrrole 2 and benzyl
chloride 3a were encapsulated inside the nanocontainer C.
long run, the reaction exclusively provides the thermodynamic
product -4. Summarizing, the calculations confirm the
catalytically relevant role of the capsule and particularly, the
calculations highlight that the capsule exerts a supramolecular
control on the reaction determining the preferential formation of
the -4 product. In fact, from the results of the secondary-order
perturbation theory (SOPT) analysis of the Fock matrix in NBO
basis (Table S8 and Figure S34), clearly emerges that the -
adducts -I and -I1 in Figure 2 are stabilized by a series of
delocalizations, involving principally the chlorine atom of 3a and
the antibonding orbital of the O–H single bond of the capsule. This
is in accordance with an enhanced transfer, at the Wheland
intermediate, of the acidic water proton to the chlorine atom
(Figure S32). Summarizing, the computational studies here
reported clearly indicate a stabilization of the Wheland -
complexes -I and -I1 inside the hexameric capsule with respect
to those occurring in the bulk solvent, and consequently a
lowering of the activation barrier of the FC reaction. In fact,
comparison of the activation barrier Gibbs free energy of the rate-
limiting step for the FC reaction revealed a very high value (-TS1,
G‡ = 50.5 kcal/mol, Table S7) when the reaction between 2 and
3a occurred in the absence of the hexameric capsule. In addition,
the calculations indicated that inside C the [1,2]-H shift and the
[1,2]-benzyl shift can occur justifying the preference for -4.
Interestingly, by doubling the percentage of C (52%) and by
increasing the reaction temperature at 50 °C, the products 4 were
obtained in 81% of total yield with a marked regioselectivity for -
4 (-4/-4 = 94/6, entry 4 in Table 1). These results suggested a
products inhibition[14] probably due to a high affinity of the
benzylated products -4 for the capsule. In fact, the catalytic
efficiency of C was dramatically lowered when the reaction in
Scheme 1 was performed in the presence of products 4 (94/6 -
4/-4 mixture of regioisomers, SI pages S5–S7).
To get more insights into the reaction mechanism that lead to the
preferential formation of -4 inside the hexameric capsule C
(Scheme 2), we conducted a quantum chemical investigation of
the effect of the capsule on the course of the FC reaction between
2 and 3a, using a capsule model CR with shorter feet and ONIOM
method (Scheme 2 and SI, pages S30–S39). Our calculations
clearly indicated that C is capable to host benzyl chloride 3a
followed by the N-methylpyrrole 2. In fact, an enthalpic
stabilization was calculated (Table S6) for the encapsulated
reagent 3a principally due to the formation of a hydrogen bonding
interaction between the chlorine atom and a bridged water
molecule in CR (Figure S30 and MC in Figure 2). Interestingly, the
pKa calculation of all hydrogen atoms directly bonded to oxygens
in the CR model (Table S11), pointed out that there are four
localized zones with a microenvironmental pKa of 2.5 while the
mean pKa results of 6.1, in excellent agreement with the
experimental datum (vide supra). In addition, a highly negative
complexation enthalpy (Table S6) was observed for the formation
of the hetero-binary complex [2+3a]@CR (Figure S31). The
calculations indicate that the reaction proceeds through -TS1
(Figure S33, Scheme 2) which lead to the corresponding Wheland
intermediate, -I (Scheme 2 and Figure 2), located 1.2 kcal/mol
below TS1 (SI, Table S7, and Figure S33). Finally, the loss of the
hydrogen atom from the -complex -I (Figures S30,S31)
proceeds very easily thanks to a very low energetic barrier (Figure
S33, 0.2 kcal/mol) and the obtained product -4 is located 9.40
kcal/mol (Figure S33) below the starting reagents making the
reaction exergonic. At this point, the keystone to justify the
marked preference for the product -4 is the [1,2]-benzyl shift
(Scheme 2 and Figure 2) which rearranges the -I adduct in the
-I1 through the transition state -I/-I1-TS with an activation
energy of 25.4 kcal/mol. On the other hand, the -complex, -I1,
not being able to directly lose the -proton (Scheme 2 and Figure
2), since posteriorly localized respect to the chlorine atom (Figure
2), undergoes a [1,2]-H shift, through -TS2, to give the Wheland
intermediate -I2, more stable than -I1 by 5.2 kcal/mol. From the
-complex, -I2, the product -4, was obtained through a re-
aromatization step with a very low energy barrier (Figure S32).
Interestingly,
the
encapsulated
product
-4@CR
is
Figure 2. Geometries for all S and TS states associated with the path in Scheme
2 for the FC reaction. Only the atoms of the ONIOM high layer have been
represented; the capsule has been omitted for clarity. Along the path, the
chlorine atom of 3a is always engaged in a hydrogen bond with a water molecule
of CR. The distances are given in Å. Carried out with CYLview.
thermodynamically more stable than -4@CR by 2.8 kcal/mol.
The calculations indicate that the retro-FC from -4 to -I proceed
with a low energy barrier (6.1 kcal/mol) and consequently, in the
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Finally, the calculations indicated a high affinity of -4 to the
capsule (H = –16.6) justifying the experimentally observed
inhibition of the nanoreactor. From the comparison of the Wiberg
bond indexes (Table S9) between the encapsulated reactants and
the other intermediates up to the product, it is evident the
formation of a catalytically relevant hydrogen bond between the
Cl atom of 3a and a bridged water molecule of CR, that reaches
its maximum value at the -I@CR (0.135), -I2@CR (0.199), and
-I/-I1-TS@CR (0.154), accomplished by a change in the charge
of the chlorine atom that reaches its maximum negative value at
the same stationary points.
dimethoxybenzene[3b] and could be due to a stronger affinity of
mesitylene for the capsule and consequently to its more efficient
encapsulation. Another hypothesis could concern a possible
product inhibition by 6. To shed light on this aspects, we
performed a competition experiment in which an equimolar
mixture of 2,3-dimethoxybenzene (1.5 equiv) and mesitylene (1.5
equiv) was mixed with benzyl chloride (1.0 equiv) in the presence
of C (52%) in water saturated CDCl3 (Scheme 3).
Under these conditions, the products 5 and 6 were isolated by
chromatographic column in 72% and 19% yield, respectively. This
result excludes a product inhibition by 6 that would also inhibit the
formation of 5. In conclusion, when the FC reaction occurs inside
the inner space of the self-assembled capsule C, the benzylation
of mesitylene is favored with respect to the 2,3-
dimethoxybenzene despite its greater nucleophilicity.
To corroborate the catalytic role of this H-bonding interaction,
we studied the reaction in Scheme 2 using benzyl iodide 3d as
the substrate, because the iodine atom in 3d is a weaker H-bond
acceptor.[15] Interestingly, when N-methylpyrrole 2 was reacted
with benzyl iodide 3d in the presence of hexameric capsule C, no
conversion to 4 was observed. Differently, by using benzyl fluoride
3b and benzyl bromide 3c the products 4 were obtained in 75 and
72% yield, with a /regioselectivity of 85/15 and 91/9,
respectively. In addition, when D2O-saturated CDCl3 was used
under the condition reported in Table 1, entry 4, the products 4
were obtained in 51% yield (Figure S1, bottom), a value
significantly lower than that observed in the presence of H2O
(81%). This result is in full accordance with the deuterium isotope
effect on H-bonding.[16]
Figure 3. Products obtained by reactions of arenes with benzyl chloride in the
presence of C. Reaction conditions: arene (0.22 M), 3a (0.15 M), C (0.076 M) in
1.1 mL of water-saturated CDCl3 at 50 °C, 16 h. Isolated yields (%). aFrom m-
c
xylene. bFrom p-xylene.
From N-methylindole; contains 16% of the
corresponding 2-isomer. dFrom anisole; contains 6% of the ortho-isomer. e From
phenol; contains 35% of the ortho-isomer. From 1,3,5-trimethoxybenzene;
f
contains 6% of the di-substituted product. gFrom toluene; contains 18% of the
ortho-isomer. h From ethylbenzene; contains 15% of the ortho-isomer. i From
thiophene; contains 40% of the 3-isomer. j From 2-bromothiophene.
Scheme 3. Competition FC benzylation experiment between mesitylene and
1,3-dimethoxybenzene promoted by C capsule. Reaction time, 4 h.
The hexameric capsule C was able to promote the benzylation
of scarce -nucleophiles such as toluene and ethylbenzene to
give derivatives 13 and 14 with good regioselectivity (para/ortho
ratio of 82/18 and 85/15 respectively). Analogously, when the m-
xylene was reacted with benzyl chloride 3a in the presence of C,
at 50 °C for 16 h, the corresponding mono-benzylated product 7
(Figure 3) was obtained in high yield (91%). Differently, the para-
xylene isomer was converted to 8 with a lower yield (49%, Figure
3). This is an interesting result since the benzylation of these
scarce -nucleophiles (toluene, ethylbenzene, xylenes) is
reported in the presence of metal catalysts (AlCl3, FeCl3, InCl3,
etc.),[17] and generally occurs with low selectivity and requiring
stoichiometric amounts of catalyst.[18] Regarding other arenes and
heteroarenes systems, a high yield was observed also in the
alkylation of N-methylindole with benzyl chloride in the presence
of C, to give the benzylated derivative 9 in 81% yield. Anisole and
phenol were efficiently benzylated to 10 and 11, respectively. In
the case of 11, a 35% of the ortho isomer was detected in the
crude product. When thiophene was mixed with benzyl chloride
At this point, we studied the scope of the FC reaction
promoted by C exploring a variety of -nucleophiles. Previously,
Mayr and coworkers reported a comparison of the nucleophilicity
parameters of typical -systems reacting with electrophiles.[3b] On
the basis of the nucleophilicity scale reported by Mayr,[3b] we
choose the series of aromatic substrates. First of all, our attention
was focused on two arenes with different position along the
Mayr’s scale,[3b] such as mesitylene and 2,3-dimethoxybenzene.
Surprisingly, when mesitylene was reacted with benzyl chloride
3a at 50 °C in the presence of C, the benzylated product 5 was
obtained in 92% yield after
4
h, whereas the 2,3-
dimethoxybenzene afforded the 4-benzylated product 6 in only
40% yield under the same conditions. This surprising higher
reactivity of mesitylene was in contrast with its position in the
Mayr’s scale of nucleophilicity with respect to 1,3-
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Chem. Eur. J. 2017, 23, 7142-7151; c) M. De Rosa, P. La Manna, A.
Soriente, C. Gaeta, C. Talotta, P. Neri, RSC Adv. 2016, 6, 91846-91851;
d) M. De Rosa, C. Talotta, A. Soriente, Lett. Org. Chem. 2009, 6, 301-
305; e) A. Soriente, M. De Rosa, M. Fruilo, L. Lepore, C. Gaeta, P. Neri,
Adv. Synth. Catal. 2005, 347, 816-824.
3a in the presence of C in water-saturated CDCl3 (Figure 3) the
monobenzylated derivative 15 was obtained in high yield (80%).
Differently by N-methylpyrrole 2, in this case, the -regioisomer
was favored with a / regioselectivity ratio of 67/33.
[10] When the N-methyl pyrrole was reacted with 4-methoxybenzyl halides
(Cl, Br) a mixture 8/2 of regioisomers (2/3) was obtained: reference 3b.
[11] a) S. Pratihar, S. Roy, J. Org. Chem. 2010, 75, 4957-4963; b) T. A. Nigst,
M. Westermaier, A. R. Ofial, H. Mayr, Eur. J. Org. Chem. 2008, 2369-
2374; c) When the tert-butylbenzyl fluoride was used in the presence of
an electrophilic organofluorophosphonium catalyst then a mixture 1:1 of
two regioisomers was formed: J. T. Zhu, M. Perez, D. W. Stephan,
Angew. Chem., Int. Ed. 2016, 55, 8448-8451; d) C. Schmuck, D.
Rupprecht, Synthesis (Stuttg) 2007, 3095-3110; analogously, Darbeau
and White showed that a 1:1 mixture of 2/3 regioisomers was obtained
when N-methylpyrrole was benzylated in the presence of nitroso amide
derivatives: e) R. W. Darbeau, E. H. White, J. Org. Chem. 1997, 62,
8091-8094.
In conclusion, we have here shown for the first time, that the
H-bond donor ability of the bridged water molecules of hexameric
resorcinarene capsule C can be exploited to promote the FC
benzylation of several arenes and heteroarenes. C is able to exert
a supramolecular control on the reaction at different levels. Inside
the inner space of C, N-methylpyrrole was preferentially
benzylated in the  position. The less -nucleophilic mesitylene
reacts faster than 1,3-dimethoxybenzene, because of its stronger
affinity for the capsule. From these data, it is clear that the
exploitation of H-bond donor ability of the bridged water molecules,
here highlighted, opens up new potentialities in the
supramolecular catalysis mediated by the fascinating self-
assembled nanocontainer C.
[12] a) J. Chen, J. Rebek, Org. Lett. 2002, 4, 327-329; b) T. Iwasawa, E. Mann,
J. Rebek, J. Am. Chem. Soc. 2006, 128, 9308-9309; c) E. Wanigasekara,
C. Gaeta, P. Neri, D. M. Rudkevich, Org. Lett. 2008, 10, 1263-1266; d)
for examples of supramolecular control of the reaction outcome with the
hexameric capsule see: ref. 6 and ref. 7e; e) A. Cavarzan, A. Scarso, P.
Sgarbossa, G. Strukul, J. N. H. Reek, J. Am. Chem. Soc. 2011, 133,
2848-2851.
Keywords: supramolecular catalysis • self-assembled capsule •
Friedel-Crafts • resorcinarene • H-bond activation
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This article is protected by copyright. All rights reserved.

10.1002/anie.201801642
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
A little bit of water is necessary to
promote a Friedel-Crafts benzylation of
π-nucleophiles inside the hexameric
resorcinarene capsule. The activation of
C-Cl bond of BnCl occurs through H-
bonding interactions with the bridged
Pellegrino La Manna, Carmen Talotta,
Giuseppe Floresta, Margherita De
Rosa,* Annunziata Soriente, Antonio
Rescifina,* Carmine Gaeta,* and Placido
Neri
Page No. – Page No.
water molecules of the capsule.
A
supramolecular control of the capsule on
the reaction outcome is evidenced.
Thus, N-methylpyrrole is preferentially
benzylated in the unusual -position,
while mesitylene reacts faster than 1,3-
dimethoxybenzene.
Supramolecularly-Driven Mild Friedel-
Crafts Reaction Inside the Hexameric
Resorcinarene Capsule: C-Cl Bond
Activation by H-Bonding with the
Bridged Water Molecules
This article is protected by copyright. All rights reserved.