A Metal-Organic Framework Br?nsted Acid Catalyst: Synthesis, Characterization and Application to the Generation of Quinone Methides for [4+2] Cycloadditions

Article abstract of DOI:10.1002/adsc.201600364

A Br?nsted acid-derived metal-organic framework (MOF) has been developed to serve as an efficient heterogeneous catalyst for a [4+2] cycloaddition. Aromatic sulfonyl groups were successfully installed using commercially available anhydridic reagents during post-synthetic modifications. The MIL-101-NH-RSO₃H MOF catalyst was fully characterized by SEM, PXRD, FTIR, TGA and N₂adsorption/desorption isotherm. Furthermore, a novel [4+2] cycloaddition of substituted 2-vinyl-substituted phenol was evaluated. The MIL-101-NH-RSO₃H catalyst showed superior catalytic capabilities when compared to a few other strong homogeneous Br?nsted acid catalysts. The MIL-101-NH-RSO₃H catalyst is compatible with a variety of substituted substrates and it can be recycled five times without loss of yield or selectivity. (Figure presented.).

Full text of DOI:10.1002/adsc.201600364

COMMUNICATIONS
DOI: 10.1002/adsc.201600364
A Metal-Organic Framework Brønsted Acid Catalyst: Synthesis,
Characterization and Application to the Generation of Quinone
Methides for [4+2] Cycloadditions
Chao Qi,a Daniele Ramella,b Allison M. Wensley,c and Yi Luana,*
a
School of Materials Science and Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian
District, Beijing 100083, Peopleꢀs Republic of China
Fax : (+86)-1-0623-33765; phone: (+86)-1-0823-76882; e-mail: yiluan@ustb.edu.cn
Temple University-Beury Hall, 1901, N. 13th Street, Philadelphia, PA 19122, USA
Catabasis Pharmaceuticals – One Kendall Square, Suite B14202, Cambridge MA 02139, USA
b
c
Received: April 6, 2016; Revised: May 19, 2016; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600364.
Abstract: A Brønsted acid-derived metal-organic
framework (MOF) has been developed to serve as
an efficient heterogeneous catalyst for a [4+2] cy-
cloaddition. Aromatic sulfonyl groups were success-
fully installed using commercially available anhydri-
dic reagents during post-synthetic modifications.
The MIL-101-NH-RSO3H MOF catalyst was fully
characterized by SEM, PXRD, FTIR, TGA and N2
covery, severe equipment corrosion and environmen-
tal pollution.[3] Metal-organic frameworks (MOFs) are
emerging as a new class of heterogeneous catalysts
thanks to their highly tailorable nature, porous struc-
ture and large surface area.[4] The Lewis acidity of
MOFs has been extensively explored while the
Brønsted acidity of MOFs needs further study.[5] Sev-
eral studies on Brønsted acid MOF bearing a pre-in-
stalled sulfonic group have been reported.[6] However,
the number of successful Brønsted acid MOFs re-
mains limited due to the narrow range of available
carboxylate ligands bearing a pre-installed sulfonic
acid group.[7] Further functionalization of porous
MOFs using a post-synthetic modification (PSM)
strategy could provide a wide variety of novel func-
tionalized MOFs.[8] However, more approaches for
the formation of Brønsted acid MOF structures are
necessary for the generation of highly acidic MOF
material.[9]
adsorption/desorption
isotherm.
Furthermore,
a novel [4+2] cycloaddition of substituted 2-vinyl-
substituted phenol was evaluated. The MIL-101-
NH-RSO3H catalyst showed superior catalytic capa-
bilities when compared to a few other strong homo-
geneous Brønsted acid catalysts. The MIL-101-NH-
RSO3H catalyst is compatible with a variety of sub-
stituted substrates and it can be recycled five times
without loss of yield or selectivity.
Keywords: Brønsted acids; [4+2] cycloaddition;
metal-organic frameworks; post-synthetic modifica-
tion; quinone methides
Hetero-Diels–Alder (HDA) reactions are among
the most useful processes in the synthesis of heterocy-
cles with a broad range of structural complexity.[10]
ortho-Quinone methides (o-QM) are important re-
agents for HDA reactions because of their tendency
to promote rapid rearomatization. ortho-Quinone me-
Although mineral Brønsted acids, such as H2SO4 and thides readily undergo cycloaddition with a variety of
HCl, have been commonly used for industrial chemi- 2p partners to generate benzannulated tetrahydropyr-
cal production for more than a century, the past few ans, common core structures of natural products.[11]
decades have featured the development of several Among these structures, chromanes have been suc-
Brønsted acid organocatalysts designed ad hoc to en- cessfully prepared by HDA reactions of dienophiles
hance organic syntheses.[1] The implementation of with an o-quinone methide.[12] However, only a few
facile methods for the introduction of Brønsted acidic examples[13] have been reported for the synthesis of
functionalities on target organic molecules is there- 4H-chromene derivatives. This approach is challeng-
fore very important.[2] Specifically, heterogeneous ing as the HDA strategy to access 4H-chromenes re-
Brønsted acid catalysts are highly desirable as an al- quires unreactive alkynes as 2p partners. One could
ternative to traditional homogeneous ones, which are imagine that a tandem [4+2]/elimination transforma-
subject to intrinsic limitations such as difficulty of re- tion may result in 4H-chromenes starting from the
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
corresponding 2p partners. Alternatively, a diverse
range of initiation methodologies has been used to
generate o-QMs. The most common method for o-
QM generation is the elimination of a stable mole-
cule, typically a benzylic substituent. The generated
benzylic carbocation subsequently tautomerizes to the
desired o-QM intermediate. We propose that the mild
protonation of 2-ethynylphenol may result in a similar
benzylic carbocation intermediate.
In this work, we report the application of a novel
Brønsted acid metal-organic framework in an efficient
[4+2] cycloaddition/elimination reaction involving an
ortho-quinone methide intermediate. The use of com-
mercially available o-sulfobenzoic acid anhydride re-
agent for the synthesis of a MIL-101-NH-RSO3H
MOF catalyst is highly convenient. To the best of our
Scheme 1. Schematic illustration of the post-synthetic modi-
fication of MIL-101-NH2.
MIL-101-NH2 crystals appear to have a spherical
knowledge, aromatic sulfonic acid groups have not morphology with a diameter of 200 nm, as measured
previously been incorporated into the framework of by SEM. No change in the morphology of the crystals
an MOF structure. Furthermore, this new way of ob- could be observed in the SEM images acquired after
taining 4H-chromenes using
a 2-vinyl-substituted the post-synthetic modification with o-sulfobenzoic
phenol as the quinone methide precursor has not acid anhydride PSM (Figure 1). The MIL-101-NH2
been reported yet. The newly synthesized heterogene- MOF support displays excellent thermal and acid sta-
ous MIL-101-NH-RSO3H catalyst is able to promote bility; as observed during the post-synthetic treatment
such a synthesis with an excellent catalytic efficiency. of MIL-101-NH2 and the catalyst recycling test.
A variety of substituted 4H-chromenes was generated
The successful synthesis of chromium-derived MIL-
from different 2-vinyl-substituted phenols. A deuteri- 101 MOFs was confirmed by powder X-ray diffraction
um labelling experiment was conducted to reveal the (PXRD) studies (Figure 2). The acid modification
internal reaction mechanism. The synthesized MIL- using o-sulfobenzoic acid anhydride did not cause de-
101-NH-RSO3H catalyst can be readily filtered and struction of the crystalline structure, which is signifi-
separated from the reaction solution, allowing for the cantly more stable than that of zinc-derived IRMOF-
recycle and reuse of the catalyst.
3.[15] MIL-101-NH2 remained chemically stable in the
MIL-101-NH2 was prepared from 2-aminotereph- presence of o-sulfobenzoic acid anhydride, successful-
thalic acid (NH2-H2BDC), according to a literature ly providing MIL-101-NH-RSO3H, as confirmed by
procedure.[14] Subsequently, it was modified post-syn- a very similar PXRD pattern (Figure 2).
thetically to afford MIL-101-NH-RSO3H using o-sul-
The modification ratio of the aromatic sulfonic
1
fobenzoic acid anhydride in chloroform. MIL-101- moiety was measured by H NMR. NMR studies of
NH-RSO3H was characterized and found to be topo- the digested sample which indicated that 30% of the
logically identical to its precursor MIL-101-NH2 MOF amino groups were post-synthetically function-
(Scheme 1).
alized (Figure 3 and the Supporting Information, Fig-
Figure 1. SEM of (left) MIL-101-NH2 and (right) MIL-101-NH-RSO3H.
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
as the optimal result to allow the free entry and exit
of the substrate molecule into the framework struc-
ture.
The successful installation of the sulfonic acid
group has also been characterized by FT-IR (Support-
ing Information, Figure S2). The new peak at
1020 cmÀ1 corresponds to the SO2 functional group
and peaks at 2850, 2920 cmÀ1 belongs to the hydrated
OH group on the sulfonic acid moiety.
MIL-101-NH2 is a highly porous MOF material
with a BET surface area of 1987 m2 gÀ1, calculated by
nitrogen adsorption isotherms collected for the MIL-
101-NH2 MOF. MIL-101-NH-RSO3H has a calculated
surface area of 1040 m2 gÀ1, which is compromised in
comparison to that of its precursor (Figure 4). The
post-synthetic modification of MIL-101-NH2 caused
a decrease in BET surface area due to the occupation
of the pore structure with the aromatic sulfonic func-
tional group. The surface area reduction usually has
no negative impact on the catalytic reactivity since
the catalytic reaction is not highly sensitive to the
available surface area as calculated by N2 adsorption.
The MIL-101-NH2 and MIL-101-NH-RSO3H were
Figure 2. PXRD of (a) MIL-101-NH2, (b) MIL-101-NH-
RSO3H and (c) recycled MIL-101-NH-RSO3H.
ure S1). The modification ratio can be easily tuned by
alternating the amount of anhydride and reaction examined by thermal gravimetric analysis (TGA) to
temperature. However, the ratio of 30% was chosen test their thermal and structural stability. Like its pre-
Figure 3. 1H NMR spectra of (a) digested MIL-101-NH2 and (b) digested MIL-101-NH-RSO3H.
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 1. Reaction conditions tested for the HAD reaction
using substituted 2-ethenylphenol.[a]
En- Catalyst (mol%)
try
Time Solvent
Yield[b]
1
2
3
4
MIL-101-NH-RSO3H (1) 24 h
CH3OH 23%
CH3CN 17%
MIL-101-NH-RSO3H (1) 24 h
MIL-101-NH-RSO3H (1) 3 h
MIL-101-NH-RSO3H (1) 3 h
MIL-101-NH-RSO3H (1) 3 h
DCE
PhCH3
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
78%
81%
95%
<5%
<5%
58%
13%
<10%
<5%
Figure 4. Nitrogen adsorption/desorption isotherms of (a)
MIL-101-NH2 and (b) MIL-101-NH-RSO3H.
5
6[c]
7
–
24 h
3 h
3 h
3 h
3 h
3 h
MIL-101-NH2 (5)
p-TsOH (1)
TFA (1)
HCl (1)
AcOH (1)
8
9
10
11
cursor MIL-101-NH2, the MIL-101-NH-RSO3H MOF
catalyst showed great thermal stability. The DSC
result indicated that the catalytic material is thermally
stable within the reaction temperature range
(Figure 5).
Our initial investigation was guided by the hypothe-
sis that 1,1-diphenylethylene could generate o-qui-
none methide through tautomerization of the benzylic
carbocation. Model compound 2a was prepared by
[a]
2.0 mmol 2a with the indicated catalyst at 508C, unless
otherwise noted.
Isolated yield.
[b]
[c]
Reaction was conducted under 1008C.
a literature procedure.[11d] Then 2a was subjected to and 508C was found to be the optimal temperature
reaction in the presence of the MIL-101-NH-RSO3H for the [4+2] cycloaddition/elimination reaction to
catalyst in MeOH to trap the possible o-quinone me- generate 3a. Remarkably, MIL-101-NH-RSO3H gave
thide intermediate (Table 1, entry 1). To our surprise, the desired 4H-chromene product in almost quantita-
4H-chromene 3a was generated as the major product tive yield after 3 h in chlorobenzene (Table 1,
alongside with other side products. Further screening entry 5). A series of control experiments (entries 6–
indicated that aprotic solvents (e.g., DCE, PhCH3, 12) was also conducted, demonstrating the unique
PhCl) appeared to be the ideal (Table 1, entries 3–5), property of the MIL-101-NH-RSO3H catalyst. Ther-
mal conditions (1008C, no catalyst) and conditions
with the basic MIL-101-NH2 only afforded trace
amounts of 3a (entries 6 and 7). Use of Brønsted
acidic p-toluenesulfonic acid (p-TsOH) at 1 mol%
gave a moderate yield with a higher catalyst loading
(Table 1, entry 8). The unsatisfactory yield was due to
the incompleteness of the chromene formation reac-
tion pathway, which left a significant amount of reac-
tion intermediate 4 (Scheme 2). Furthermore, tri-
fluoroacetic acid (TFA), hydrogen chloride and acetic
acid only showed minimal reactivity at 508C after 3 h,
presumably because of the low acidity in terms of
their pKa (Table 1, entries 9–11). The turn-over
number (TON) of MIL-101-NH-RSO3H under the
optimized reaction conditions calculated to be 95.
Using the optimized conditions, we examined the
robustness of the synthetic procedure. A broad range
of 1,1-diphenylethylenes (2a–2i) was tested, obtaining
good to excellent yields. The reaction showed good
tolerance toward a wide range of functional groups,
Figure 5. TGA of (a) MIL-101-NH2 and (b) MIL-101-NH-
RSO3H.
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
Scheme 2. Mechanistic studies.
such as methoxy, methyl, and halogens (Table 2, 3a– creased yields in only 3 h. The decreasing yield of 3e
3d). In addition, very electron-rich aromatic rings, may be due to the instability of the methylenedioxy
such as 3,4-benzodioxole also afforded good yields moiety under the acidic conditions. The naphthyl-sub-
(3e, 77% yield). Steric effects and meta substitution stituted ethylene (2i) also afforded the desired prod-
patterns were also tested using substrates with tert- uct 3i in good yield.
butyl and methoxy groups, respectively; each provid-
To gain further insights into the reaction mecha-
ing the desired product in good yield (3f–3g). Gener- nism, additional experiments were performed. When
ally, more electron-rich functional groups provide in- 2a was treated with 1 mol% of pTsOH, the key reac-
Table 2. Substrate scope of the MIL-101-NH-RSO3H catalyst-driven protonation, HDA and elimination cascade reaction.[a]
[a]
2.0 mmol of substrate 2 and 0.2 mmol of MIL-101-NH-RSO3H were dissolved in 3.0 mL of PhCl and stirred at 508C for
3 h. The yield was calculated based on the amount of isolated product.
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
(Scheme 4). The hydrogen bond between quinone
methide 7 and the phenolic proton led to the syn ge-
ometry between the methyl group and the p-OMe
phenyl group in 4 (cf Scheme 2). Adduct 4 was fur-
ther treated with MIL-101-NH-RSO3H catalyst,
which led to quantitative formation of 3a
(Scheme 2b). Additionally, when 2a was subjected to
1 mol% MIL-101-NH-RSO3H at room temperature,
we were also able to isolated a trace amount of
adduct 4 with the same relative stereochemistry.
These results indicate that MIL-101-NH-RSO3H is
also able to catalyze elimination of phenol (cf
Scheme 2).
We ran a deuterium exchange reaction to afford
deuterated phenol intermediate 5 (Scheme 3). Under
thermal conditions, reaction of 5 did not show any
deuterium migration to the vinyl position in 6. This
result allows us to exclude the possibility of a 1,5-hy-
dride shift[16] mechanism for the generation of the qui-
Scheme 3. Deuterium labelling study.
tion intermediate 4 was isolated as the dominant dia- none methide species.
stereomer (dr>10:1). The relative stereochemistry of On the basis of the aforementioned experimental
was assigned based on the NOE analysis results and mechanistic findings, a possible mecha-
4
(Scheme 2a and the Supporting Information, Fig- nism is proposed in Scheme 4. Electron enriched 1,1-
ure S3). The high diastereoselectivity indicates that diphenylethylene 2a is protonated by MIL-101-NH-
a concerted cycloaddition mechanism is more likely RSO3H to form quinone methide 7. Intermediate 7
than a stepwise cation cycloaddition-based mechanism reacts with another equivalent of 2a through a con-
Scheme 4. Proposed mechanism for the MIL-101-NH-RSO3H-promoted [4+2] catalytic reaction.
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
certed hetero-Diels–Alder reaction to afford dimeric catalyst loadings, an improvement over several other
compound 4. Under acidic condition, the 4-MeO-2- strong homogeneous Brønsted acid catalysts. It is also
phenol group is preferentially protonated to afford in- compatible with a variety of 2-vinyl-substituted phe-
termediate 8. Driven by steric effects, the fully substi- nols, affording good yields and excellent diastereose-
tuted C-2 eliminates to generate oxonium species 10, lectivities. Mechanistic studies further revealed the
along with a 3-methoxyphenol 9. Oxonium 10 is de- advantage of using our heterogeneous Brønsted acid
protonated by the basic residue in MIL-101-NH- catalyst, as well as the ortho-quinone methide forma-
RSO3H catalyst to afford 3a.
tion mechanism. The MIL-101-NH-RSO3H catalyst
In order to examine the recyclability of the MIL- was chemically stable and did not suffer from a leach-
101-NH-RSO3H catalyst, it was isolated and reused in ing problem during catalysis; making the catalyst
five reactions. The catalyst was centrifuged from the highly recyclable. Further studies aimed at developing
reaction solution and washed with chloroform. The new applications of the MIL-101-NH-RSO3H catalyst
strong covalent bond between the aromatic sulfonic are in progress.
acid moiety and amino group on MIL-101-NH-
RSO3H ensures the chemical stability of the active
sites, which remains good, affording up to 93% yield Experimental Section
after five reuses of the same batch of catalyst
(Figure 6). Furthermore, the supernatant liquid of the Preparation of MIL-101-NH-RSO3H
chlorobenzene suspension showed no catalytic reac-
MIL-101-NH2 was prepared from 2-aminoterephthalic acid
tivity toward the vinylphenol substrate, which is evi-
dence for no leakage of the MIL-101-NH-RSO3H cat-
alyst. The X-ray powder diffraction pattern and SEM
spectra of the MIL-101-NH-RSO3H catalyst after five
times reuse were also indistinguishable from those of
the fresh catalyst (Figure 2 and the Supporting Infor-
mation, Figure S3). The catalytic reaction solution
was analyzed by ICP-AES and showed no detectable
amount of chromium ion in the solution. These facts
clearly demonstrate that there was no leaching or cat-
alyst decomposition over the catalytic process
(Figure 2).
In conclusion, a novel and efficient heterogeneous
MIL-101-NH-RSO3H catalyst bearing an aromatic
sulfonic acid group was achieved via a simple and
rapid one-step PSM approach. The structural mor-
phology of MIL-101-NH-RSO3H was well retained
after post-synthetic modification and MIL-101-NH-
RSO3H was characterized in detail. The newly devel-
oped MIL-101-NH-RSO3H showed high activity and
selectivity in generating quinone methide for the
[4+2] cycloaddition/elimination reaction at very low
(NH2-H2BDC), according to a literature procedure.[14] Sub-
sequently, it was modified post-synthetically using o-sulfo-
benzoic acid anhydride in chloroform to afford MIL-101-
NH-RSO3H.
Catalytic Reaction Conditions
For a general catalytic reaction, 1 mol% of the MIL-101-
NH-RSO3H was added to 1.00 mL PhCl, which was in an
oven-dried round-bottom reaction vessel. 1.0 mmol of sub-
strate was added successively. The solution was stirred at
508C for 3 h. The reaction mixture was passed through
a silica gel plug and eluted with 5 mL of dichloromethane.
Then, the filtrate was concentrated under reduced pressure
and the residue was purified by flash chromatography over
silica gel to afford the dimeric product. The yield was calcu-
lated based on the isolated product.
Acknowledgements
We thank the National Natural Science Foundation of China
(No. 51503016) and Fundamental Research Funds for the
Central Universities FRF-TP-15–001A2. The authors grate-
fully acknowledge Philip N. Moquist for helpful discussion
of the manuscript.
References
[1] a) C. H. Cheona, H. Yamamoto, Chem. Commun. 2011,
47, 3043–3056; b) S. Liang, G. B. Hammond, B. Xu,
Chem. Commun. 2015, 51, 903–906; c) T. Akiyama, J.
Itoh, K. Fuchibe, Adv. Synth. Catal. 2006, 348, 999–
1010.
[2] a) Y. Luan, N. Zheng, Y. Qi, J. Yu, G. Wang, Eur. J.
Inorg. Chem. 2014, 36, 4268–4272; b) D. Britt, C. Lee,
F. J. Uribe-Romo, H. Furukawa, O. M. Yaghi, Inorg.
Chem. 2010, 49, 6387–6389.
Figure 6. MIL-101-NH-RSO3H catalyst recycling.
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
asc.wiley-vch.de
[3] a) S. M. George, Chem. Rev. 1995, 95, 475–476; b) Y.
Chang, C. Bae, Curr. Org. Synth. 2011, 8, 208–236;
c) O. Kwon, S. Park, G. Seo, Chem. Commun. 2007, 43,
4113–4115; d) S. Liang, J. Jasinski, G. B. Hammond, B.
Xu, Org. Lett. 2015, 17, 162–165; e) X. Huang, A. Gos-
wami, X. Zou, S. Hayes, V. Shah, T. Minko, Z. Tao, T.
Asefa, BioNanoScience 2014, 4, 27–36; f) H. Zhang, X.
Lin, S, Chin, M. W. Grinstaff, J. Am. Chem. Soc. 2015,
137, 12660–12666; g) C. Qi, T. Qin, D. Suzuki, J. A. Por-
co Jr, J. Am. Chem. Soc. 2014, 136, 3374–3377.
[4] a) A. Corma, H. Carcia, F. X. Llabrꢂs, I. Xamena,
Chem. Rev. 2010, 110, 4606–4655; b) A. Dhakshina-
moorthy, M. Opanasenko, J. Cejka, H. Garcia, Catal.
Sci. Technol. 2013, 3, 2509–2540; c) I. Hod, P. Deria, W.
Bury, J. E. Mondloch, C.-W. Kung, M. So, M. D. Samp-
son, A. W. Peters, C. P. Kubiak, O. K. Farha, J. T. Hupp,
Nat. Commun. 2015, 6, 8304;.
[5] a) B. Li, K. Leng, Y. Zhang, J. J. Dynes, J. Wang, Y. Hu,
D. Ma, Z. Shi, L. Zhu, D. Zhang, Y. Sun, M. Chrzanow-
ski, S. Ma, J. Am. Chem. Soc. 2015, 137, 4243–4248;
b) L. Mitchell, B. Gonzalez-Santiago, J. P. S. Mowat,
M. E. Gunn, P. Williamson, N. Acerbi, M. L. Clarke,
P. A. Wright, Catal. Sci. Technol. 2013, 3, 606–617; c) R.
Srirambalaji, S. Hong, R. Natarajan, M. Yoon, R. Hota,
Y. Kim, Y. H. Ko, K. Kim, Chem. Commun. 2012, 48,
11650–11652; d) M. Zheng, Y. Liu, C. Wang, S. Liub,
W. Lin, Chem. Sci. 2012, 3, 2623–2627; e) J. Wang, C.
Qi, Z. Ge, T. Chen, R. Li, Chem. Commun. 2010, 46,
2124–2126.
[6] a) J. Juan-Alcaniz, R. Gielisse, A. B. Lago, E. V.
Ramos-Fernandez, P. Serra-Crespo, T. Devic, N. Guil-
lou, C. Serre, F. Kapteijn, J. Gascon, Catal. Sci. Technol.
2013, 3, 2311–2318; b) Y. D. Zang, J. Shi, F. M. Zhang,
Y. J. Zhong, W. D. Zhu, Catal. Sci. Technol. 2013, 3,
2044–2049.
[8] V. Valtchev, V. G. Majano, S. J. Perez-Ramirez, Chem.
Soc. Rev. 2013, 42, 263–290.
[9] a) M. B. Gawande, A. K. Rathi, I. D. Nogueira, R. S.
Varma, P. S. Branco, Green Chem. 2013, 15, 1895–1899;
b) M. G. Goesten, J. Juan-Alcaniz, E. V. Ramos-Fer-
nandez, K. B. Sai Sankar Gupta, E. Stavitski, H. van
Bekkum, J. Gascon, F. Kapteijn, J. Catal. 2011, 281,
177–187; c) B. Li, Y. Zhang, D. Ma, L. Li, G. Li, G. Li,
Z. Shi, S. Feng, Chem. Commun. 2012, 48, 6151–6153;
d) S. J. Garibay, Z. Wang, S. M. Cohen, Inorg. Chem.
2010, 49, 8086–8091; e) Y. Liu, X. Xi, C. Ye, T. Gong,
Z. Yang, Y. Cui, Angew. Chem. Int. Ed. 2014, 126,
14041–14045; f) Y. Luan, S. E. Schaus, J. Am. Chem.
Soc. 2012, 134, 19965–19968; g) Y. Luan, K. S. Barbato,
P. N. Moquist, T. Kodama, S. E. Schaus, J. Am. Chem.
Soc. 2015, 137, 3233–3236.
[10] V. Eschenbrener-Lux, K. Kumar, H. Waldmann,
Angew. Chem. 2014, 126, 11326–11337; Angew. Chem.
Int. Ed. 2014, 53, 11146–11157.
[11] a) A. B. Turner, Q. Rev. Chem. Soc. 1964, 18, 347–360;
b) J. Zhao, S. Sun, S. He, Q. Wu, F. Shi, Angew. Chem.
2015, 127, 5550–5554; Angew. Chem. Int. Ed. 2015, 54,
5460–5464; c) C. Hsiao, S. Raja, H. Liao, I. Atodiresei,
M. Rueping, Angew. Chem. 2015, 127, 5854–5857;
Angew. Chem. Int. Ed. 2015, 54, 5762–5765; d) W.-X.
Zhao, Z.-B. Wang, B.-Y. Chu, J.-W. Sun, Angew. Chem.
2015, 127, 1930–1933; Angew. Chem. Int. Ed. 2015, 54,
1910–1913; e) C. Qi, H. Cong, K. Cahill, P. Mꢃller, J. A.
Porco Jr, Angew. Chem. 2013, 125, 8503–8506; Angew.
Chem. Int. Ed. 2013, 52, 8345–8348.
[12] a) S. B. Ferreira, F. C. Silva, A. C. Pinto, D. T. G. Gon-
zaga, V. F. Ferreira, J. Heterocycl. Chem. 2009, 46,
1080–1097; b) N. Willis, C. D. Bray, Chem. Eur. J. 2012,
18, 9160–9173.
[13] M. Fujiwara, M. Sakamoto, K. Komeyama, H. Yoshida,
K. Takaki, J. Heterocycl. Chem. 2015, 52, 59–66.
[14] Y. Lin, C. Kong, L. Chen, RSC Adv. 2012, 2, 6417–
6419.
[7] a) J. Jiang, O. M. Yaghi, Chem. Rev. 2015, 115, 6966–
6997; b) M. Lammert, S. Bernt, F. Vermoortele, D. E.
De Vos, N. Stock, Inorg. Chem. 2013, 52, 8521–8528;
c) Y. Luan, Y. Qi, H. Y. Gao, R. S. Andriamitantsoa,
N. N. Zheng, G. Wang, J. Mater. Chem. A 2015,
##25##3, 17320–17331; d) Y. Zhou, Y. Chen, Y. Hu, G.
Huang, S. Yu, H. Jiang, Chem. Eur. J. 2014, 20, 14976–
14980.
[15] Y. Luan, Y. Qi, H. Gao, N. Zheng, G. Wang, J. Mater.
Chem. A 2014, 2, 20588–20596.
[16] a) O. R. Martin, S. P. Rao, H. A. El-Shenawy, K. G.
Kurz, A. B. Cutler, J. Org. Chem. 1988, 53, 3287–3292;
b) C. Qi, Y. Xiong, V. Eschenbrenner-Lux, C. Cong,
J. A. Porco Jr, J. Am. Chem. Soc. 2016, 138, 798–801.
Adv. Synth. Catal. 0000, 000, 0 – 0
8
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!

COMMUNICATIONS
A Metal-Organic Framework Brønsted Acid Catalyst:
Synthesis, Characterization and Application to the
Generation of Quinone Methides for [4+2] Cycloadditions
9
Adv. Synth. Catal. 2016, 358, 1 – 9
Chao Qi, Daniele Ramella, Allison M. Wensley, Yi Luan*
Adv. Synth. Catal. 0000, 000, 0 – 0
9
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!