Intermolecular Carbonyl–olefin Metathesis with Vinyl Ethers Catalyzed by Homogeneous and Solid Acids in Flow

Article abstract of DOI:10.1002/anie.201909597

The carbonyl–olefin metathesis reaction has experienced significant advances in the last seven years with new catalysts and reaction protocols. However, most of these procedures involve soluble catalysts for intramolecular reactions in batch. Herein, we show that recoverable, inexpensive, easy to handle, non-toxic, and widely available simple solid acids, such as the aluminosilicate montmorillonite, can catalyze the intermolecular carbonyl–olefin metathesis of aromatic ketones and aldehydes with vinyl ethers in-flow, to give alkenes with complete trans stereoselectivity on multi-gram scale and high yields. Experimental and computational data support a mechanism based on a carbocation-induced Grob fragmentation. These results open the way for the industrial implementation of carbonyl–olefin metathesis over solid catalysts in continuous mode, which is still the origin and main application of the parent alkene–alkene cross-metathesis.

Full text of DOI:10.1002/anie.201909597

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201909597
German Edition: DOI: 10.1002/ange.201909597
Flow Chemistry
Intermolecular Carbonyl–olefin Metathesis with Vinyl Ethers
Catalyzed by Homogeneous and Solid Acids in Flow
Miguel ꢀngel Rivero-Crespo+, Marꢁa Tejeda-Serrano+, Horacio Pꢂrez-Sꢃnchez,
Josꢂ Pedro Cerꢄn-Carrasco, and Antonio Leyva-Pꢂrez*
Abstract: The carbonyl–olefin metathesis reaction has expe-
rienced significant advances in the last seven years with new
catalysts and reaction protocols. However, most of these
procedures involve soluble catalysts for intramolecular reac-
tions in batch. Herein, we show that recoverable, inexpensive,
easy to handle, non-toxic, and widely available simple solid
acids, such as the aluminosilicate montmorillonite, can catalyze
the intermolecular carbonyl–olefin metathesis of aromatic
ketones and aldehydes with vinyl ethers in-flow, to give alkenes
with complete trans stereoselectivity on multi-gram scale and
high yields. Experimental and computational data support
a mechanism based on a carbocation-induced Grob fragmen-
tation. These results open the way for the industrial imple-
mentation of carbonyl–olefin metathesis over solid catalysts in
continuous mode, which is still the origin and main application
of the parent alkene–alkene cross-metathesis.
alkene, and Prins couplings.[8] To circumvent these drawbacks,
we envisaged the use of vinyl ethers as alkene partners in the
intermolecular carbonyl–olefin metathesis, since the gener-
ation of unreactive esters instead of competing aldehyde/
ketone as by-products may shift the equilibrium towards the
products, facilitate the catalytic action not only of metal salts,
but also of simple solids acids, and enable an easy purification
of the alkene products by column chromatography (Support-
ing Information, Figure S1).[9]
Table 1 shows selected catalytic results for the metathesis
reaction between aromatic ketones and aldehydes 1a,b with
vinyl ethers 2a,b, where different Lewis acids (FeCl3,
BF3·OEt2) and Brçnsted acids (HOTf) give significant yields
of trans alkenes 3a,b at room temperature (entries 1–7, no cis
alkenes detected by gas chromatography, GC; see also
Tables S1–S3 and Figures S2,S3 in the Supporting Informa-
tion). Notice that these metal salts are well-known active
T
he direct transformation of carbonyl compounds into
alkenes is now moving from stoichiometric and waste-
generating Wittig-type protocols to more efficient catalytic
processes.[1] Among them, the carbonyl–olefin metathesis
reaction stands out by the availability and low price of the
starting materials, redox neutrality, and simplicity of retro-
synthetic disconnections, akin to parent alkene cross-meta-
thesis.[2] However, in contrast to the latter, only one solid
precursor has apparently been reported for the carbonyl–
olefin metathesis,[3,4] with just two substrates in 15–30%
yields.[5] The lack of solid catalysts for the carbonyl olefin
metathesis comes from the extreme acidity required for the
catalyst to increase the reaction rate towards the final
carbonyl/alkene products, that is, the pKa of soluble acids
employed so far is well below 0, particularly those involving
intermolecular reactions.[6,7] Thus, it is difficult to think of
a conventional solid with the level of acidity required for the
transformation which does not concomitantly triggers other,
more favorable, acid catalyzed reactions such as the aldol,
Table 1: Selected results of the catalyst screening for the carbonyl–olefin
metathesis of ketones 1a or aldehyde 1b with vinyl ethers 2a,b
(1.5 equiv.) in batch (see complete screening in the Supporting
Information). Yields reported for isolated products after complete
consumption of 2a,b or 20 h reaction time.
Entry Catalyst (mol%)
T [8C] Carbonyl/vinyl
Product (%
yield)
ether
1[a]
2
3
4
5
6
7
8
9
10
11
12
13
FeCl3 (50)
25
25
60
25
25
25
25
60
60
60
100
60
1a/2a
1b/2b
1b/2b
1a/2a
1b/2b
1a/2a
1b/2b
1b/2b
1b/2b
1b/2b
1b/2b
1b/2b
1b/2b
3a (51)
3b (24)
3b (25)
3a (56)
3b (64)
3a (45)
3b (56)
3b (58)
3b (38)
3b (6)
BF3·OEt2 (50)
HOTf (50)
HOTf (10)
[*] Dr. M. ꢀ. Rivero-Crespo,[+] M. Tejeda-Serrano,[+] Dr. A. Leyva-Pꢁrez
Instituto de Tecnologꢂa Quꢂmica (UPV-CSIC), Universitat Politꢃcnica
de Valꢃncia-Consejo Superior de Investigaciones Cientꢂficas
Avda. de los Naranjos s/n, 46022 Valencia (Spain)
E-mail: anleyva@itq.upv.es
NafionTM (50)
Amberlyst A15 (50)
Zeolite HUSY (50)
3b (38)
3b (16)
3b (45)
MCM-41 (50)
Montmorillonite K10 60
(50)
Dr. H. Pꢁrez-Sꢄnchez, Dr. J. P. Cerꢅn-Carrasco
Structural Bioinformatics and High Performance Computing
Research Group (BIO-HPC), Universidad Catꢅlica de Murcia
(UCAM) (Spain)
14
100
1b/2b
1b/2b
3b (65)
3b (87)
15[b] Montmorillonite K10 100
(5)
[+] These authors contributed equally to the work.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/anie.201909597.
[a] No reaction with anhydrous FeCl3. [b] In-flow reaction: 1b in toluene
0.5m, 0.01 mLminÀ1 over 8 h at 1208C (see Figure 1 for a 40 h reaction
time experiment).
Angew. Chem. Int. Ed. 2019, 58, 1 – 5
ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
catalysts for intramolecular carbonyl olefin metathesis but not
for intermolecular reactions.[10]
A freshly open sample of anhydrous FeCl3, used in
a glovebox, did not catalyze the metathesis reaction. How-
ever, when 50 mol% of water were added, the metathesis
reaction started. Addition of a proton quencher such as di-
tert-butyl pyridine to the reaction medium (50 mol%) stops
not only the metathesis but also any other parasite reaction
(aldol, hydrolysis of the vinyl ether, etc.), for all the soluble
catalysts tested. These results indicate that in situ formed
protons are also the catalytically active species during the
metal salt-catalyzed intermolecular carbonyl–olefin metathe-
sis, and with this in mind and the positive results obtained for
soluble Brçnsted acids, a variety of commercially-available
solid acids (entries 8–15) were tested as catalysts for the
metathesis (Supporting Information, Table S4).[11] The results
in Table 1 show that all the solid Brçnsted acid catalysts tested
gave similar product yields and selectivity to the soluble acids
for alkene product 3b, including the widely available, inex-
pensive, and non-toxic pillared clay montmorillonite K10
(<10 euroskgÀ1, entries 14–15). The ester by-products 4a,b
are completely unreactive under the present reaction con-
ditions for any catalyst, according to control experiments, and
the purification of the final alkene products by column
chromatography becomes easier in the absence of additional
alkene/aldehydes/ketones in the mixture. These results support
our starting hypothesis that vinyl ethers are suitable alkene
partners for the intermolecular carbonyl–olefin metathesis.
A convenient and productive way to circumvent side
reactions during the intermolecular metathesis could be to
perform the reaction in flow over a fixed-bed reactor with
a solid catalyst, in order to rapidly separate the acid catalyst
from the reaction mixture after the metathesis reaction.
Gratifyingly, a consistent good yield of 3b (70–95%, GC)
over 8 h in-flow reaction time was obtained with fixed-bed
montmorillonite K10 (entry 15 in Table 1). Figure 1 (top)
shows that the procedure with montmorillonite K10 in
continuous mode is also suitable to prepare a variety of
trans alkenes in high yields after just 1 h on stream time
(condition A), generally in better yields than with soluble
BF3·OEt2 catalyst in batch (condition B). The main side
reaction corresponds to vinyl ether hydrolysis, which explains
the better reactivity of the in situ generated vinyl ethers from
acetals 2a–g (see also Figure S4 in the Supporting Informa-
tion).[12] Good to moderate yields are generally obtained, and
some functional groups are shown to be tolerated, including
halides (compounds 3g, 3i–l), aromatic ethers (3g), esters
(3n), amides (3t), thioethers (3v), and other alkenes (3x).
Figure 1 (bottom) shows that montmorillonite K10 is still
active after 40 h in-flow, which gives a turnover number
(TON) of 150, which is significantly higher than homogeneous
catalysts.[3] This backs up the robustness of the solid catalyst to
give access to multi-gram amounts of alkene 3b. Furthermore,
the selectivity towards the alkene product is consistently
higher than 90%, highlighting the benefits of performing the
reactions in flow with a solid catalyst (see also Table S5 in the
Supporting Information).
Figure 1. Top: Carbonyl olefin metathesis reactions of aryl aldehydes
1b,d–i with in situ formed vinyl ether 2d–g catalyzed by montmorillon-
ite K10 (A) or BF3·OEt2 (B) under the indicated reaction conditions.
Bottom: Kinetic profile for the metathesis reaction between 1b and 2d
in a fixed-bed tubular reactor with montmorillonite K10 catalyst (0.5m
toluene, 0.01 mLminÀ1 over 40 h at 1208C). Color Scheme: starting
aldehyde 1b in red, alkene product 3b in green, selectivity in blue.
Error bars account for a 5% uncertainty.
Brçnsted acids, correlate well with the pKa of the catalyst
for the homogeneous acids and also for montmorillonite K10,
and deviate towards higher values for other solid acids (see
also Figure S5, and Figure S6 in the Supporting Information
for entropy correlation).[11b] Kinetic experiments at different
stirring rates show that the reaction is controlled by diffusion
for all solid catalysts except for montmorillonite K10,[13] which
strongly supports the assumption that the reaction enthalpy is
directly related to proton strength.
Figure 3 (top) shows experimental and computational
evidences about the mechanism of the reaction (see also
Figure S7 and Table S6 in the Supporting Information). A
Hammett plot with different para-substituted acetophenones
(Supporting Information, Figure S8) gives 1 = À2.7, which
Figure 2 shows that the activation enthalpy values for the
metathesis reaction between 1b and 2b with different
2
www.angewandte.org
ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2019, 58, 1 – 5
These are not the final page numbers!

Angewandte
Communications
Chemie
elusive when using the most accepted photochemical meth-
ods, in accordance with the lack of efficient reported methods
for a-hydroxyoxetanes.[14] These results point to the formation
of a cationic intermediate during the metathesis reaction.
Indeed, the activation entropy for homogeneous acids is
negative (the expected value for an associative transition
state) but positive for solids, including montmorillonite K10,
which is consistent with an extra-stabilized carbocation
transition state within the anionic aluminosilicate framework
(Supporting Information, Figure S6).[11b]
Figure 3 also shows that the isotopically labelled ketone
1d-18O[15] gives an ester by-product that does not contain any
labelled oxygen atom, while the addition of one equivalent of
H218O in the reaction medium generates a significant amount
of isotopically labelled ester. Control experiments without 2a
confirm that no O atom exchange occurs in the absence of the
vinyl ether (Supporting Information, Figure S9). These results
unveil that the alkene product actually comes from a water-
mediated carbonyl–olefin metathesis and not from a direct
transferring of the carbonyl oxygen atom, which seems to be
accepted in the literature as a formal carbonyl–olefin meta-
thesis reaction[7c] (see also Figure S10 and Table S7 in the
Supporting Information).[16] These results strongly support
the participation of external alcohol or water molecules as
nucleophiles during reaction.
Figure 2. Activation enthalpy (KJmolÀ1) for the carbonyl–olefin meta-
thesis of 1b with 2b with different acids. Aluminosilicates were dried
under vacuum at 2508C for 3 h before reaction. Linear regression,
R2 =0.88. Error bars account for a 5% uncertainty.
Figure 3 (middle) shows a reaction mechanism consistent
with all the experimental data described above. The first step
is the nucleophilic attack of the vinyl ether on the proton-
activated carbonyl group, which, after hemiacetal formation
and acid- catalyzed dehydration, generates a suitable anti-
a hydroxyl carbocation to undergo a Grob fragmentation[17]
and give the final trans alkene.[18] Density functional theory
(DFT) calculations were then conducted for the proton-
catalyzed metathesis reaction between 1b and 2a, without
imposing any geometrical restriction to reactants, products,
and transition states, and with vibrational calculations to
confirm the nature of the located minima in the potential
energy surface, including solvent effects.[19] Figure 3 (bottom)
shows that the most favorable mechanism, highlighted in blue,
consists of the proton-catalyzed nucleophilic attack of 2a to
1b through a barrier of 6.3 kcalmolÀ1 to give the thermody-
namically favorable aldol-like adduct, 15.4 kcalmolÀ1 more
stable than the parent reactants and in equilibrium with the
corresponding hemi-acetal (only differing in 2.0 kcalmolÀ1),
which then triggers a proton transfer to the vicinal hydroxyl
group to give the carbocation. The latter reaction is the
limiting step of the process, with an energetic barrier of
22.4 kcalmolÀ1, after which the Grob fragmentation proceeds
with a barrier of 5.9 kcalmolÀ1 to give the final trans alkene
product (20.5 kcalmolÀ1 more stable than 1b and 2a). The
alternative mechanism through the oxetane, highlighted in
red, is kinetically impeded by 5.1 kcalmolÀ1 compared to
acetal formation, and with a reversion energy barrier of only
1 kcalmolÀ1 from the oxetane to the aldol adduct. All
accumulated experimental and theoretical evidences strongly
support carbocation formation and later Grob fragmentation
as plausible mechanism for this metathesis reaction.[6a,7c]
In conclusion, the intermolecular carbonyl–olefin meta-
thesis of aromatic aldehydes and ketones with vinyl ethers
Figure 3. Experimental evidences (top) and plausible reaction mecha-
nism (middle) for the acid-catalyzed metathesis reaction between
aromatic aldehydes/ketones and vinyl ethers. Computed energy profile
(bottom) for the proton-catalyzed metathesis of 1b and 2a. Color
Scheme for atoms: carbon in grey, oxygen in red, and hydrogen in
white. Blue and red curves stand for the reaction through the acetal
and oxetane intermediates, respectively.
indicates building of positive charge on the carbonyl group in
the rate-determining step of the reaction. No traces of
oxetane could be detected during the reaction, and the
preparation of the postulated oxetane intermediate was
Angew. Chem. Int. Ed. 2019, 58, 1 – 5
ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
Franzꢁn, Chem. Commun. 2018, 54, 12982 – 12985; c) L. Pitzer,
F. Sandfort, F. Strieth-Kalthoff, F. Glorius, Angew. Chem. Int.
Ed. 2018, 57, 16219 – 16223; Angew. Chem. 2018, 130, 16453 –
16457; d) U. P. N. Tran, G. Oss, D. P. Pace, J. Ho, T. V. Nguyen,
Chem. Sci., 2018, 9, 5145 – 5151; e) U. P. N. Tran, G. Oss, M.
Breugst, E. Detmar, D. P. Pace, K. Liyanto, T. V. Nguyen, ACS
Catal. 2019, 9, 912—919.
catalyzed by fixed-bed Brçnsted solid acids or, alternatively,
by metal salts or conventional Brçnsted acids in solution, has
been accomplished. Mild solid acids, particularly the alumi-
nosilicate montmorillonite K10, catalyze the intermolecular
reaction with vinyl ethers by shifting the equilibrium towards
the alkene products and by stabilizing intermediate carboca-
tions formed during the reaction. These results enable the
synthesis of trans alkenes in continuous flow by intermolec-
ular carbonyl–olefin metathesis, with potential applications as
simple building blocks in chemical industry.[20]
[8] J. D. Lewis, S. Van de Vyver, Y. Romꢂn-Leshkov, Angew. Chem.
Int. Ed. 2015, 54, 9835 – 9838; Angew. Chem. 2015, 127, 9973 –
9976.
[9] a) F. R. Fortea-Pꢁrez, M. Mon, J. Ferrando-Soria, M. Boronat,
A. Leyva-Pꢁrez, A. Corma, J. M. Herrera, D. Osadchii, J.
Gascon, D. Armentano, E. Pardo, Nat. Mater. 2017, 16, 760 – 766;
b) J. Oliver-Meseguer, M. Boronat, A. Vidal-Moya, P. Concep-
cion, M. A. Rivero-Crespo, A. Leyva-Pꢁrez, A. Corma, J. Am.
Chem. Soc. 2018, 140, 3215 – 3218; c) M. A. Rivero-Crespo, M.
Mon, J. Ferrando-Soria, C. W. Lopes, M. Boronat, A. Leyva-
Pꢁrez, A. Corma, J. C. Hernandez-Garrido, E. Lopez-Haro, J. J.
Calvino, E. V. Ramos-Fernandez, D. Armentano, E. Pardo,
Angew. Chem. Int. Ed. 2018, 57, 17094 – 17099; Angew. Chem.
2018, 130, 17340 – 17345; d) M. Tejeda-Serrano, M. Mon, B.
Ross, F. Gonell, J. Ferrando-Soria, A. Corma, A. Leyva-Perez,
D. Armentano, E. Pardo, J. Am. Chem. Soc. 2018, 140, 8827 –
8832.
Acknowledgements
Financial support by MINECO through the Severo Ochoa
program (SEV-2016-0683), Excellence program (CTQ 2017-
86735-P, CTQ 2017-87974-R), Retos Col. (RTC-2017-6331-5),
and “Convocatoria 2014 de Ayudas Fundaciꢀn BBVA
a Investigadores y Creadores Culturales” is acknowledged.
M.A.R.-C. and M.T.-S. thank ITQ for the concession of
a contract. This research was partially supported by the
supercomputing infrastructure of Poznan Supercomputing
Center.
[10] a) L. Ma, W. Li, H. Xi, X. Bai, E. Ma, X. Yan, Z. Li, Angew.
Chem. Int. Ed. 2016, 55, 10410 – 10413; Angew. Chem. 2016, 128,
10566 – 10569; b) C. C. McAtee, P. S. Riehl, C. S. Schindler, J.
Am. Chem. Soc. 2017, 139, 2960 – 2963; c) S. Niyomchon, A.
Oppedisano, P. Aillard, N. Maulide, Nat. Commun. 2017, 8, 1091;
d) R. B. Watson, C. S. Schindler, Org. Lett. 2018, 20, 68 – 71;
e) E. J. Groso, A. N. Golonka, R. A. Harding, B. W. Alexander,
T. M. Sodano, C. S. Schindler, ACS Catal. 2018, 8, 2006 – 2011;
f) H. Albright, P. S. Riehl, C. C. McAtee, J. P. Reid, J. R. Ludwig,
L. A. Karp, P. M. Zimmerman, M. S. Sigman, C. S. Schindler, J.
Am. Chem. Soc. 2019, 141, 1690 – 1700.
Conflict of interest
The authors declare no conflict of interest.
Keywords: carbonyl–olefin metathesis ·
heterogeneous catalysis · in-flow reactions ·
montmorillonite K10 · vinyl ethers
´
[11] a) M. Sliwa, K. Samson, M. Ruggiero-Mikołajczyk, A. Zelazny,
R. Grabowski, Catal. Lett. 2014, 144, 1884 – 1893; b) J. R.
Cabrero-Antonino, A. Leyva-Perez, A. Corma, Angew. Chem.
Int. Ed. 2015, 54, 5658 – 5661; Angew. Chem. 2015, 127, 5750 –
5753.
[12] a) P. G. Gassman, S. J. Burns, J. Org. Chem. 1988, 53, 5574 – 5576;
b) T. Yamamoto, T. Eki, S. Nagumo, H. Suemune, K. Sakai,
Tetrahedron 1992, 48, 4517 – 4524; c) S. Nagumo, A. Matsukuma,
H. Suemune, K. Sakai, Tetrahedron 1993, 49, 10501 – 10510;
d) H. Suemtme, O. Yoshida, J. Uchida, Y. Nomura, M. Tanaka,
K. Sakai, Tetrahedron Lett. 1995, 36, 7259 – 7262.
[13] For a review see B. S. Kumar, A. Dhakshinamoorthy, K.
Pitchumani, Catal. Sci. Technol. 2014, 4, 2378 – 2396.
[14] a) R. Pꢁrez-Ruiz, M. A. Miranda, R. Alle, K. Meerholz, A. G.
Griesbeck, Photochem. Photobiol. Sci. 2006, 5, 51 – 55; b) M.
DꢃAuria, R. Racioppi, Molecules 2013, 18, 11384 – 11428.
[15] T. B. Mete, T. M. Khopade, R. G. Bhat, Tetrahedron Lett. 2017,
58, 2822 – 2825.
[16] A. Corma, V. R. Ruiz, A. Leyva-Perez, M. J. Sabater, Adv.
Synth. Catal. 2010, 352, 1701 – 1710.
[17] a) K. Prantz, J. Mulzer, Chem. Rev. 2010, 110, 3741 – 3766.
[18] Y. D. Gong, H. Tanaka, N. Iwasawa, K. Narasaka, Bull. Chem.
Soc. Jpn. 1998, 71, 2181 – 2185.
[19] Y. Zhao, D. G. Truhlar, Acc. Chem. Res. 2008, 41, 157 – 167.
[20] C. Copꢁret, F. Allouche, K. W. Chan, M. P. Conley, M. F. Delley,
A. Fedorov, I. B. Moroz, V. Mougel, M. Pucino, K. Searles, K.
Yamamoto, P. A. Zhizhko, Angew. Chem. Int. Ed. 2018, 57,
6398 – 6440; Angew. Chem. 2018, 130, 6506 – 6551.
[1] M. R. Becker, R. B. Watson, C. S. Schindler, Chem. Soc. Rev.
2018, 47, 7867 – 7881.
[2] a) A. K. Griffith, C. M. Vanos, T. H. Lambert, J. Am. Chem. Soc.
2012, 134, 18581 – 18584; b) J. R. Ludwig, P. M. Zimmerman,
J. B. Gianino, C. S. Schindler, Nature 2016, 533, 374 – 379; c) J. R.
Ludwig, S. Phan, C. C. McAtee, P. M. Zimmerman, J. J. Devery
III, C. S. Schindler, J. Am. Chem. Soc. 2017, 139, 10832 – 10842.
[3] For reviews on carbonyl olefin metathesis, see: a) J. R. Ludwig,
C. S. Schindler, Synlett 2017, 28, 1501 – 1509; b) T. H. Lambert,
Synlett 2019, ahead of print.
[4] For examples of solid-catalyzed low-temperature alkene meta-
thesis, see: a) V. Mougel, K.-W. Chan, G. Siddiqi, K. Kawakita,
H. Nagae, H. Tsurugi, K. Mashima, O. Safonova, C. Copꢁret,
ACS Cent. Sci. 2016, 2, 569 – 576; b) M. D. Korzynski, D. F.
Consoli, S. Zhang, Y. Romꢂn-Leshkov, M. Dinca, J. Am. Chem.
Soc. 2018, 140, 6956 – 6960.
[5] H.-P. van Schaik, R.-J. Vijn, F. Bickelhaupt, Angew. Chem. Int.
Ed. Engl. 1994, 33, 1611 – 1612; Angew. Chem. 1994, 106, 1703 –
1704.
[6] For pure Bronsted acid-catalyzed reactions, see: a) J. R. Ludwig,
R. B. Watson, D. J. Nasrallah, J. B. Gianino, P. M. Zimmerman,
R. A. Wiscons, C. S. Schindler, Science 2018, 361, 1363 – 1369;
b) L. Catti, K. Tiefenbacher, Angew. Chem. Int. Ed. 2018, 57,
14589 – 14592; Angew. Chem. 2018, 130, 14797 – 14800.
[7] For intermolecular reactions, see: a) N. V. Ramesh, J. Bah, J.
Franzꢁn, Eur. J. Org. Chem. 2015, 1834 – 1839; b) S. Ni, J.
Manuscript received: July 30, 2019
Accepted manuscript online: September 20, 2019
Version of record online: && &&, &&&&
4
www.angewandte.org
ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2019, 58, 1 – 5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Flow Chemistry
M. ꢁ. Rivero-Crespo, M. Tejeda-Serrano,
H. Pꢂrez-Sꢃnchez, J. P. Cerꢄn-Carrasco,
A. Leyva-Pꢂrez*
&&&& — &&&&
Intermolecular Carbonyl–olefin
Metathesis with Vinyl Ethers Catalyzed by
Homogeneous and Solid Acids in Flow
The intermolecular carbonyl–olefin meta-
thesis between aromatic ketones/alde-
hydes and vinyl ethers is accomplished
with not only simple soluble but also
solid acid catalysts to give trans alkenes in
high yields, multi-gram amounts, and in-
flow.
Angew. Chem. Int. Ed. 2019, 58, 1 – 5
ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!