Copper-Catalyzed Allylic C?H Alkynylation by Cross-Dehydrogenative Coupling

Article abstract of DOI:10.1002/chem.201801772

C?H bond functionalization is a well-developed concept that has been thoroughly studied and gives entry to rather complex molecules without the need for previous derivatization of the substrates. The use of copper complexes in allylic C?H bond functionalization under oxidative conditions as an alternative to the well-established palladium-based methodologies remains largely underdeveloped. Here, we show for the first time a selective cross-dehydrogenative coupling reaction between underivatized allylic substrates and terminal alkynes to produce 1,4-enynes in high yields in a single step, using an in situ synthesized copper catalyst and an oxidant.

Full text of DOI:10.1002/chem.201801772

A Journal of
Accepted Article
Title: Copper-Catalyzed Allylic C-H Alkynylation via Cross-
Dehydrogenative Coupling
Authors: Ahmad A. Almasalma and Esteban Mejía
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201801772
Link to VoR: http://dx.doi.org/10.1002/chem.201801772
Supported by

10.1002/chem.201801772
Chemistry - A European Journal
COMMUNICATION
Copper-Catalyzed Allylic C-H Alkynylation via Cross-
Dehydrogenative Coupling
Ahmad A. Almasalma[a] and Esteban Mejía*[a]
Abstract: C-H bond functionalization is a well-developed concept
that has been thoroughly studied and gives entry to rather complex
molecules without the need of previous derivatization of the
substrates, although the use of copper complexes for allylic C-H
bond functionalization under oxidative conditions as an alternative to
the well-established palladium-based methodologies remains largely
underdeveloped. Here we show for the first time a selective cross-
dehydrogenative coupling reaction between underivatized allylic
substrates and terminal alkynes to produce 1,4-enynes in high yields
in a single step, using an in situ synthesized copper catalyst and an
oxidant.
C-H functionalization is a fairly active research field,[9] when
compared to the amount of research done on Pd systems, one
can fairly say that is still underdeveloped. Most of the efforts on
this area have been focused on aromatic sp2 hetero-
derivatization[10] and on the synthesis of heterocycles.[11] Reports
on copper-catalyzed allylic C-H bond functionalization are still
scarce, even though allylic oxidation with peresters is known for
a long time (as the Kharash-Sosnovsky reaction).[12] Other allylic
C-H heterofunctionalyzation reactions have being developed,
namely
aminations[13]
and
phosphonations.[14]
Allylic
trifluoromethylation is one of the few rare cases by which C-C
bond formation has been achieved by means of Cu-catalyzed
allylic C-H functionalization.[15]
Allylic substitution is currently one of the most important
methods for the construction of C-C bonds and has been used
as a key step to access pharma intermediates and complex
target molecules like natural products.[1] It is usually carried out
with palladium catalysts[2] even though several metals including
copper, nickel, platinum, rhodium, iridium, ruthenium,
molybdenum and tungsten have been also explored.[3] Almost
invariably, the key intermediate of these reactions is a (π-
allyl)metal complex which can undergo a wide range of regio-,
chemo- , and stereoselective transformations (Scheme 1, A). An
important drawback of all these methodologies is that they
require electrophilic substrates with preinstalled leaving groups
Developed at the turn of the 21st century, the cross-
dehydrogenative coupling reaction (CDC), is a powerful and
elegant methodology for the formation of C-C bonds using two
different C-H moieties.[16] Following this breakthrough, various
efficient methods have been developed for sp3 C–H bond
functionalization and subsequent coupling with sp, sp2 and sp3
C–H bonds under relatively mild reaction conditions with good
selectivity.[16a, 17] One apparent limitation of the CDC approach is
that most derivatizations occur at α-C–H bond to heteroatoms
such as nitrogen and oxygen due to the prompt formation of
iminium and oxonium ions respectively, under oxidative
conditions (Scheme 1, B).[18]
at the allylic position like halides, phosphonates acetoxy, amino,
3b, 4]
hydroxyl and carbonates.[1,
The installation of these
functional groups requires additional synthetic steps, and
narrows the scope of this transformation. Therefore, the direct
utilization of allylic C–H bonds as C-C bond coupling substrates
is of high interest. Transition-metal catalyzed C-H bond
functionalization offers a good alternative to overcome these
problems.[5] These processes are atom-economic, make
synthesis protocols shorter and reduce the amount of produced
waste (metal salts), leading to sustainable processes, an
ultimate goal of our modern society in which environmental
concerns are of highest priority.
Most of the developed C-H functionalization methodologies
relies on the functionalization of C–H bonds at sp2 carbons,
especially from electron-rich heterocycles and directing group-
containing arenes,[6] for both, kinetic and thermodynamic
reasons, the metal-catalyzed C–H functionalization at sp3
carbons devoid of functional groups is more challenging than
that at its sp2 hybridized congeners,[7] with the exception of C-H
bonds at benzylic and allylic positions.[8] Although copper-based
Scheme 1. C-C Bond forming methodologies relevant to this work (general
scheme). R, R’, R’’= alkyl or aryl; LG= leaving group; Nu= nucleophile
(organyl); M= Pt or Cu); M’= main group metal (Li, MgBr); X= O or N; M’’= Cu,
Zn or Ag
In a seminal report, Li and co-workers described the first
catalytic allylic alkylation reaction coupling an allylic sp3 carbon
with a methylenic sp3-C using a combination of CuBr and CoCl2
as catalysts and a super-stoichiometric amount of tert-butyl
hydroperoxide (TBHP) as the oxidant.[19] However, the extension
of this methodology to terminal alkynes has, so far, remained
elusive.
[a]
A. A: Almasalma and Dr. E. Mejía
Leibniz Institute for Catalysis
Albert-Einstein-Straße 29a, 18059 Rostock, Germany
Esteban.Mejia@catalysis.de
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/chem.201801772
Chemistry - A European Journal
COMMUNICATION
To the best of our knowledge, this work is the first example of a
stabilization of copper(II) and (III) intermediates can be
direct allylic C(sp3)–H alkynylation reaction with terminal alkynes. anticipated (see mechanistic discussion below). Other ligands
Compared with the “classic” allylic substitution approaches
(Scheme 2),[20] this new methodology gives
more
straightforward access to 1,4-enynes, important structural
scaffolds in organic synthesis[21] and core of several compounds
of pharmaceutical relevance.[22] Thus, we hope, it might become
a valuable addition to the organic chemist’s toolbox.
common in copper chemistry like bidentate phosphines, N-
heterocyclic carbenes and phtalocyanine proved to be
ineffective.
a
Scheme 3. Optimized conditions for the allylic alkynylation reaction via CDC:
1a (1 equivalent), 2a (10 equivalents), [Cu(NCMe)4]PF6 (5 mol%), L3 (5
mol%), DTBP (2 equivalents), DMSO, 130 °C, 24 hours
Table 1. Effect of chelating pyridine ligands on the yield of 3a.
Scheme 2. Allylic C-C coupling reactions. TBHP=tert-butyl hydroperoxide;
DTBP=di-tert-butyl peroxide
We started our research by establishing the conditions for the
representative CDC reaction between phenylacetylene (1a) and
cyclohexene (2a) (Scheme 3). After an extensive screening of
various oxidants (Table S1), catalysts precursors (Table S2),
stoichiometric ratio of the reactants (Table S3), and ligands
(Table 1), we selected as the best conditions: 1a (1 equivalent),
an excess of 2a (10 equivalents), [Cu(NCMe)4]PF6 as the
catalyst precursor (5 mol%), 4'-(p-tolyl)-2,2':6',2''-terpyridine L3
as ligand (5 mol%) and DTBP as oxidant (2 equivalents) in
DMSO at 130 °C for 24 hours. Under these conditions product
3a was afforded in 70 % within 5 hours, 75% after 16 hours,
78% after 24 hours without any further increase of the yield after
48 hours.
The use of TBHP as oxidant (as reported by Li et al.) [19] proved
to be ineffective, as well as other common oxidants including
benzoyl peroxide (BPO), 1,4 benzoquinone (BQ), Cu(OAc)2 and
oxygen. The chosen ligand also showed to play an important
role on the reaction efficiency; selected examples are presented
in Chart 1. The best results were obtained with terpyridine
derivatives (L1-L7), which, compared to the commonly used
bipyridins and phenantrolines (L8, L9 and L10), can prevent
more effectively the formation of metal aggregates and other
inactive complexes by ligation of multiple substrate molecules.[23]
Moreover, considering their strong σ-donating properties, a good
This article is protected by copyright. All rights reserved.

10.1002/chem.201801772
Chemistry - A European Journal
COMMUNICATION
Table 2. Substrate scope for the allylic alkynylation reaction via CDC.a
[a] Isolated yield. [b] Using L1. [c] NMR yield …
While direct C–H alkynylation (with terminal alkynes) has
recently emerged as one of the preferred approaches to access
substituted alkynes, this transformation is still challenging due to
the facile Glaser-type homo-coupling and polymerization of
terminal alkynes under oxidative conditions.[24] In our case, the
use of a tenfold excess of cyclohexene 2a was enough to
effectively slow down the undesired dimerization of 1a that
results in the formation of 1,4-diphenylbuta-1,3-diyne (4, Table
S3).
With the best conditions at hand, we decided to investigate the
substrate scope of this transformation with different types of
terminal acetylenes (Table 2). In all cases, the major by-product
was the corresponding prop-1-yn-1-ylbenzene derivative,
resulting from the methylation of the alkyne (vide infra). In
general, phenylacetylene derivatives bearing electron-donating
substituents on the phenyl ring showed good reactivity,
furnishing the desired products in high yields (3a-3f), except
from the 4-(N,N-dimethylamino)phenylacetylene, which led only
to trace amounts of the coupling product (3g). A plausible
explanation to this caveat might be the propensity of alkyl
amines to form radicals in α-positions (to the nitrogen), resulting
in uncontrolled side reactions.[25] Interestingly, m-hydroxy
phenylacetylene could be successfully derivatized with our new
methodology without previous protection of the hydroxyl
functionality yielding the 1,4-enyne 3h in 60% yield. Electron-
deficient substrates were also reactive under these conditions,
although lower yields of 3 were obtained (3i-3n). Electron-rich
allylbenzene derivatives also proved to be effective substrates
for the CDC reaction with phenyl acetylene producing the
corresponding linear 1,4-enynes 3o and 3p in good yields and
requiring only a five-fold excess. On the contrary, reaction of the
electron-poor, CF3-substituded allyl benzene resulted only in
traces of the desired product (3q). The scope of the CDC
coupling with phenylacetylene was extended successfully to
other cycloalkanes. Although slightly lower yields were obtained
for larger rings (cyclooctene, 3r and cycloheptene, 3t) only the
desired product was observed. On the contrary, in spite of its
high reactivity (resulting on 67% conversion of 1a), the reaction
with cyclopentene afforded a mixture of isomers of difficult
separation (3s). The reaction was also successful when less
reactive aliphatic alkynes were used (3u and 3v).
In order to assess the nature of the radical species present in
the reaction mixture, radical trapping experiments using TEMPO
(2, 2, 6, 6–tetramethylpiperidin–1–yl)oxy were carried out (see
Supporting Information, Scheme S1). By adding 1 equivalent of
TEMPO to the reaction mixture 50 % of the expected product
This article is protected by copyright. All rights reserved.

10.1002/chem.201801772
Chemistry - A European Journal
COMMUNICATION
(3a) was obtained along with methylated TEMPO as the only
TEMPO-derivative. The use of higher amounts of the radical trap
(3 equivalents) resulted in complete inhibition of the cross-
fashion to produce the oxidized copper(II) complex 5.[31] This
single electron transfer (SET) reaction should be feasible
considering the inherent electrophilicity of the alkoxy radical[32]
Cu(II)/Cu(I)
coupling reaction, being the methylated TEMPO the only product. and the reductive power of [LCuI]+ (for reference: E1/2
in
These results underline the importance of the methyl radicals,
not only as a side product of the decomposition of the tert-
butoxy radicals, but as possible reaction partners for the
deprotonation of the allyl substrate 2.
water is -0.093 V vs. SCE).[33] Taking into account the known
propensity of copper(II) complexes to react with organic
34]
radicals,[27,
the formation of the transient copper(III)
intermediate 6 can be expected.[35] At the same time, the
formation of organocuprates (7) under the reaction conditions is
anticipated due to the inherent acidity of the protons of the
substrate (1).[36] Finally, ligand exchange between 6 and 7 would
lead to the formation of the copper(III) intermediate 8 which,
upon reductive elimination of the coupling product 3, shall
regenerate the copper(I) catalyst [LCuI]+.
A primary kinetic isotopic effect (see Supporting information)
was observed for C(sp3)-H bond cleavage (Scheme 4, A;
[3a]/[3a-D9] =2.8), suggesting that irreversible C(sp3)–H bond
cleavage in the cyclohexene occurs within the catalytic cycle,
although with the available data it cannot be said if it is involved
in the turnover-determining step of the overall transformation.[26]
Moreover, while no obvious kinetic isotopic effect was observed
for the C(sp)–H for phenyl acetylene (Scheme 5, B; kH/kD=0.89),
it can be concluded that C-H bond cleavage at the terminal
alkyne is not involved in the turnover-determining step (for a
detailed description on the determination of the reaction rates,
see Supporting information).
Scheme 4. Experiments for the determination of the kinetic isotope effects
(KIE)
Scheme 5. Proposed reaction mechanism for the allylic alkynylation reaction
via CDC
Although the exact underlying reaction mechanism remains
unclear, we postulate the pathway depicted in Scheme 5. In a
first step, DTBP (thermally) splits to generate two O-centered
alkoxyl radicals.[27] The formed alkoxyl radicals can selectively
abstract a hydrogen atom from the allylic position of 2 to
generate the allyl radical 4.[28] Comparison of the corresponding
bond dissociation energies (BDE, kJ/mol) of both the O-H bond
in t-BuOH ─produced when DTBP is used─ (444.9) and the
allylic C-H of propylene (368.6),[29] shows that this radical
abstraction is exergonic, hence thermodynamically favored.
Nevertheless, under our reaction conditions the formed tert-
butoxy radicals can decompose into methyl radicals and
acetone(equation 2).[30] The produced open-shell species may
then react with the copper(I) catalyst [LCuI]+ in a reductive
The cross-coupling of open-shell (radical) species have become
a powerful and attractive way to create new C-C bonds. Yet, the
hurdles associated with this process (even though the activation
energy of radical−radical coupling reactions is nearly zero), have
slowed
down
the
development
of
radical
C-H
functionalization/cross coupling processes, compared with
“classical” cross-coupling methodologies. [37] Herewith, we report
a novel methodology to achieve oxidative C–H cross-coupling of
underivatized allylic substrates (cyclic and linear) and terminal
alkynes (aromatic and aliphatic). The utilization copper(I) and a
trispyridyl ligand for this catalytic system was the key for
controlling the reaction selectivity towards the allylic alkynylation
(cross-coupling) versus the, commonly unsurmountable, alkynyl
This article is protected by copyright. All rights reserved.

10.1002/chem.201801772
Chemistry - A European Journal
COMMUNICATION
[12] a) D. J. Rawlinson, G. Sosnovsky, Synthesis 1972, 1972, 1-28; b) G.
Chelucci, A. Iuliano, D. Muroni, A. Saba, J. Mol. Catal. A: Chem. 2003,
191, 29-33.
homocoupling. It has to be noted that in order to do so, a tenfold
excess of the allylic substrate is necessary. Various substituted
1,4 enynes were synthesized in good to high yields with a good
functional group tolerance. Preliminary mechanistic studies
suggest that the reaction proceeds through cross-
dehydrogenative pathway with a primary KIE for the C-H bond
braking on the allylic substrate and the involvement of CH3
radicals from the decomposition of the oxidant DTBP. To the
best of our knowledge, this work provides the first example of a
direct allylic C(sp3)–H alkynylation with terminal alkynes, giving
access to 1,4-enynes under oxidative conditions without the
need of preinstalled leaving groups or strong organometallic
nucleophiles. Further studies towards the control of the
stereochemical outcome of the reaction, the replacement of the
oxidant and further optimization of the condition are currently
undergoing in our laboratories and will be the subject of a
separate report.
[13] R. T. Gephart, T. H. Warren, Organometallics 2012, 31, 7728-7752.
[14] B. Yang, H.-Y. Zhang, S.-D. Yang, Org. Biomol. Chem. 2015, 13, 3561-
3565.
[15] J. Xu, Y. Fu, D.-F. Luo, Y.-Y. Jiang, B. Xiao, Z.-J. Liu, T.-J. Gong, L. Liu,
J. Am. Chem. Soc. 2011, 133, 15300-15303.
[16] a) C.-J. Li, Acc. Chem. Res. 2009, 42, 335-344; b) C. Zhang, C. Tang,
N. Jiao, Chem. Soc. Rev. 2012, 41, 3464-3484; c) S. A. Girard, T.
Knauber, C.-J. Li, Angew. Chem., Int. Ed. 2014, 53, 74-100.
[17] Y. Xing, N.-X. Wang, W. Zhang, Synlett 2015, 26, 2088-2098.
[18] A. Gini, T. Brandhofer, O. G. Mancheno, Org. Biomol. Chem. 2017, 15,
1294-1312.
[19] Z. Li, C.-J. Li, J. Am. Chem. Soc. 2006, 128, 56-57.
[20] a) Y.-X. Li, Q.-Q. Xuan, L. Liu, D. Wang, Y.-J. Chen, C.-J. Li, J. Am.
Chem. Soc. 2013, 135, 12536-12539; b) A. Harada, Y. Makida, T. Sato,
H. Ohmiya, M. Sawamura, J. Am. Chem. Soc. 2014, 136, 13932-
13939; c) Y. Makida, Y. Takayama, H. Ohmiya, M. Sawamura, Angew.
Chem., Int. Ed. 2013, 52, 5350-5354; d) J. A. Dabrowski, F. Gao, A. H.
Hoveyda, J. Am. Chem. Soc. 2011, 133, 4778-4781; e) Y. Kiyotsuka, Y.
Kobayashi, J. Org. Chem. 2009, 74, 7489-7495.
Acknowledgements
[21] a) T. Sato, T. Onuma, I. Nakamura, M. Terada, Org. Lett. 2011, 13,
4992-4995; b) X. Shi, D. J. Gorin, F. D. Toste, J. Am. Chem. Soc. 2005,
127, 5802-5803; c) A. Buzas, F. Gagosz, J. Am. Chem. Soc. 2006, 128,
12614-12615; d) F. Erver, J. R. Kuttner, G. Hilt, J. Org. Chem. 2012, 77,
8375-8385; e) V. Hickmann, M. Alcarazo, A. Fürstner, J. Am. Chem.
Soc. 2010, 132, 11042-11044.
Thanks to the Analytical department at LIKAT, Rostock and Prof.
Udo Kragl (University of Rostock) for the continuous support.
Keywords: Copper • Cross Dehydrogenative Coupling • Allylic
Alkynylation • Oxidation • C-H Functionalization
[22] a) V. D. P. Nair, A. Dairam, A. Agbonon, J. T. Arnason, B. C. Foster, I.
Kanfer, J. Agric. Food Chem. 2007, 55, 1707-1711; b) S. Drewes, R. W.
Liebenberg; Roecar Holdings US4652636 A, 1987
[23] A. Kiyomori, J.-F. Marcoux, S. L. Buchwald, Tetrahedron Lett. 1999, 40,
2657-2660.
[1]
[2]
B. M. Trost, M. L. Crawley, in Topics in Organometallic Chemistry, Vol.
38 (Ed.: U. Kazmaier), Springer Berlin, Heidelberg, 2012, pp. 321-340.
a) S. Fan, F. Chen, X. Zhang, Angew. Chem., Int. Ed. 2011, 50, 5918-
5923; b) G. Liu, Y. Wu, in Topics in Current Chemistry, Vol. 292 (Eds.:
J.-Q. Yu, Z. Shi), Springer, Berlin, Heidelberg, 2010, pp. 195-209.
a) B. L. Tran, M. Driess, J. F. Hartwig, J. Am. Chem. Soc. 2014, 136,
17292-17301; b) J.-M. Begouin, J. M. N. Klein, D. Weickmann, B.
Plietker, in Topics in Organometallic Chemistry, Vol. 38 (Ed.: U.
Kazmaier), Springer, Berlin, Heidelberg, 2012, pp. 269-320; c) Y.
Nishibayashi, S. Uemura, in Comprehensive Organometallic Chemistry
III, Vol. 11 (Eds.: R. H. Crabtree, D. M. P. Mingos), Elsevier, 2007, pp.
75-122; d) G. Helmchen, U. Kazmaier, S. Förster, in Catalytic
Asymmetric Synthesis, Third ed. (Ed.: I. Ojima), John Wiley & Sons,
Inc., 2010, pp. 437-770.
[24] a) S. Tang, P. Wang, H. Li, A. Lei, Nat. Commun. 2016, 7, 11676; b) X.
Chen, H. Zhang, J. Chen, H. Gong, Chem. Lett. 2015, 44, 129-131.
[25] O. Kei, N. Takashi, F. Shunichi, Bull. Chem. Soc. Jpn. 2006, 79, 1489-
1500.
[3]
[26] E. M. Simmons, J. F. Hartwig, Angew. Chem., Int. Ed. 2012, 51, 3066-
3072.
[27] A. L. J. Beckwith, A. A. Zavitsas, J. Am. Chem. Soc. 1986, 108, 8230-
8234.
[28] a) J. K. Kochi, P. J. Krusic, J. Am. Chem. Soc. 1968, 90, 7157-7159; b)
P. C. Wong, D. Griller, J. C. Scaiano, J. Am. Chem. Soc. 1982, 104,
5106-5108.
[29] J. Hioe, H. Zipse, Org. Biomol. Chem. 2010, 8, 3609-3617.
[30] P. J. Jones, B. Riser, J. Zhang, J. Phys. Chem. A 2017, 121, 7846-
7853.
[4]
[5]
a) N. A. Butt, W. Zhang, Chem. Soc. Rev. 2015, 44, 7929-7967; b) J.-B.
Langlois, A. Alexakis, in Topics in Organometallic Chemistry, Vol. 38
(Ed.: U. Kazmaier), Springer Berlin, Heidelberg, 2012, pp. 235-268.
H. M. L. Davies, J. Hansen, in Catalytic Asymmetric Synthesis (Ed.: I.
Ojima), John Wiley & Sons, Inc., 2010, pp. 163-226.
[31] F. Chen, C. Qin, Y. Cui, N. Jiao, Angew. Chem., Int. Ed. 2011, 50,
11487-11491.
[32] B. P. Roberts, Chem. Soc. Rev. 1999, 28, 25-35.
[33] B. R. James, R. J. P. Williams, J. Chem. Soc. 1961, 0, 2007-2019.
[34] Y. L. Chow, G. E. Buono-Core, J. Am. Chem. Soc. 1986, 108, 1234-
1239.
[6]
[7]
[8]
[9]
T. W. Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147-1169.
J. A. Labinger, J. E. Bercaw, Nature 2002, 417, 507-514.
T. Jensen, P. Fristrup, Chem. Eur. J. 2009, 15, 9632-9636.
[35] A. Casitas, X. Ribas, Chem. Sci. 2013, 4, 2301-2318.
[36] Z. Li, C.-J. Li, J. Am. Chem. Soc. 2004, 126, 11810-11811.
[37] H. Yi, G. Zhang, H. Wang, Z. Huang, J. Wang, A. K. Singh, A. Lei,
Chem. Rev. 2017, 117, 9016-9085.
a) H.-Q. Do, O. Daugulis, J. Am. Chem. Soc. 2011, 133, 13577-13586;
b) J. Roane, O. Daugulis, J. Am. Chem. Soc. 2016, 138, 4601-4607; c)
X. Chen, X.-S. Hao, C. E. Goodhue, J.-Q. Yu, J. Am. Chem. Soc. 2006,
128, 6790-6791.
[10] J.-L. Hu, J. Li, Y.-F. Zhou, Curr. Green Chem. 2015, 2, 170-191.
[11] a) X.-X. Guo, D.-W. Gu, Z. Wu, W. Zhang, Chem. Rev. 2015, 115,
1622-1651; b) O. Daugulis, in Topics in Current Chemistry, Vol. 292
(Eds.: J.-Q. Yu, Z. Shi), Springer, Berlin, Heidelberg, 2010, pp. 57-84.
This article is protected by copyright. All rights reserved.

10.1002/chem.201801772
Chemistry - A European Journal
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Ahmad A. Almasalma and Esteban
Mejía*
Page No. – Page No.
Copper-Catalyzed Allylic C-H
Alkynylation via Cross-
Dehydrogenative Coupling
For the first time, a selective cross-dehydrogenative coupling reaction between
underivatized allylic substrates and terminal alkynes was achieved, in a single step,
using a copper catalyst under oxidative conditions. This new method provides direct
access to 1,4-enynes in high yields and selectivity without the need of preinstalled
leaving groups or strong organometallic nucleophiles.
This article is protected by copyright. All rights reserved.