Ni-Catalyzed Cyclization of Enynes and Alkynylboronates: Atom-Economical Synthesis of Boryl-1,4-dienes

Article abstract of DOI:10.1002/chem.201903405

We report a novel atom-economical Ni-catalyzed cyclization reaction of enynes with alkynylboronates. The reaction employs a non-expensive Ni salt, a phosphine-based ligand and easy-handling alkynylboronates as boron–carbon source. The reaction provides co

Full text of DOI:10.1002/chem.201903405

DOI: 10.1002/chem.201903405
Communication
&
Nickel Catalysis |Hot Paper|
Ni-Catalyzed Cyclization of Enynes and Alkynylboronates:
Atom-Economical Synthesis of Boryl-1,4-dienes
Natalia Cabrera-Lobera, M. Teresa Quirꢀs, Elena BuÇuel,* and Diego J. Cꢁrdenas*[a]
son to other organometallic compounds, such as organomag-
Abstract: We report a novel atom-economical Ni-cata-
nesium or organolithium reagents. Although there are many
lyzed cyclization reaction of enynes with alkynylboronates.
commercially available organoboron compounds, those with
The reaction employs a non-expensive Ni salt, a phos-
more structural complexity need to be prepared. Therefore,
phine-based ligand and easy-handling alkynylboronates as
the development of new, mild and efficient synthetic routes
boron–carbon source. The reaction provides complex
based on inexpensive and atom-economical catalytic systems
fused-bicyclic compounds containing borylated 1,4-cyclo-
are still required.
hexadienes in high yields in short reaction times, involving
Among the different described methods for the synthesis of
the formation of two CÀC bonds in one step. A reasona-
ble reaction mechanism is proposed based on mechanistic
experimental results.
organoboronates, hydroboration,[6] diboration,[7] and carbobo-
rations,[8] are the most commonly used. In particular, the latter
leads to the simultaneous formation of CÀC and CÀB bonds in
a single step. Especially interesting is the report published by
Suginome in 2003, which describes the first regioselective Ni-
catalyzed carboboration of alkynes with alkynylboronates, in
which a CÀB bond activation by oxidative addition is propo-
sed.[8d] On the other hand, our group has focused its efforts on
the development of novel borylative cyclization reactions of
polyunsaturated species, allowing the concomitant formation
of a CÀB and one or more CÀC bonds using Pd catalysis and
diboron reagents.[9] More recently, we have succeeded at de-
veloping full atom-efficient Fe-,[10] and Ni-catalyzed[11] hydro-
borylative cyclizations, using pinacolborane as the boron
source (Scheme 1). To the best of our knowledge, carboboryla-
tive cyclization reactions have no precedent in the literature.
The development of practical, simple and highly efficient syn-
thetic methods is one of the priorities of novel organic chemis-
try. We are witnessing an increasing interest in the improve-
ment of conventional methodologies to describe useful and ef-
ficient synthetic procedures, since economic and environmen-
tal aspects cannot be ignored nowadays.[1] This is one of the
reasons why the use of the first-row transition-metals has in-
creased during the last decades.[2] Catalytic reactions based on
these metals have opened up new perspectives since they pro-
vide novel activation pathways and surprising reaction mecha-
nisms, accessing to a unique chemical space.
On the other hand, organoboron compounds have been
widely employed as powerful building blocks both in synthetic
organic chemistry and medicinal chemistry, that is, alkenylbor-
onates find application as electronic materials and bioactive
natural products.[3] They can also be considered as green com-
pounds since they are non-toxic and allow reactions in water.
Organoboronates usually show a good stability to molecular
oxygen and moisture, facilitating their synthesis, purification,
isolation and storage, on top to their high functional group
compatibility. Despite their stability, organoboron compounds
still exhibit reasonable reactivity as nucleophilic partners in the
Suzuki–Miyaura cross-coupling reaction or[4] the Petasis reac-
tion,[5] among others, showing less side reactions in compari-
[a] N. Cabrera-Lobera, Dr. M. T. Quirꢀs, Dr. E. BuÇuel, Prof. D. J. Cꢁrdenas
Departamento de Quꢂmica Orgꢁnica, Facultad de Ciencias
Universidad Autꢀnoma de Madrid
Scheme 1. Metal-catalyzed borylative cyclization reactions of enynes.
Institute for Advanced Research in Chemical Sciences (IAdChem)
Av. Francisco TomꢁsyValiente 7, Cantoblanco
28049-Madrid (Spain)
E-mail: elena.bunnuel@uam.es
Herein, we report a Ni-catalyzed cyclization of enynes using
easy-handling and readily accessible alkynylboronates,[12] and a
simple and inexpensive Ni-based catalytic system. The reaction
furnishes 1,4-cyclohexadienes, proceeds with complete atom-
diego.cardenas@uam.es
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under:
https://doi.org/10.1002/chem.201903405.
Chem. Eur. J. 2019, 25, 1 – 6
1
ꢂ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
economy and shows a broad scope. As it is shown below, the
formation of the observed products does not seem to proceed
through the expected mechanism, and the reactivity of enynes
contrast with that of simple akynes.[8d]
Table 1. Scope of the Ni-catalyzed carboborylative cyclization reaction.[a–
b]
We intended to develop a carboborylative reaction analo-
gous to the hydroborylative cyclization of enynes mentioned
above,[11] by taking advantage of the previously proposed CÀB
oxidative addition of alkynylboronates to Ni. Thus, enyne 1a
was initially treated with alkynylboronate 2 (1.1 equiv), Ni(cod)2
(5 mol%) and PCy3 (20 mol%), in toluene at 808C. When the
enyne was present in the reaction medium from the begin-
ning, or when it was rapidly added to the mixture of the rest
of the reagents, only oligomerization products derived from
the enyne were observed. This was already observed by Sugi-
nome in the boryl-alkynylation of alkynes.[8d] In contrast, slow
addition of enyne 1a by a syringe pump for 1 h, led to com-
plete suppression of oligomerization, and surprisingly afforded
the unexpected compound 3a in 82% yield (Table 1). The ex-
pected isomer, which would result from a carboborylative cycli-
zation similar to those already described (4), was not observed
in any case. Further experimentation using different reaction
conditions was carried out, but neither the yield of 3a in-
creased nor other borylation products were observed (see Sup-
porting Information for details). Formation of 3a involves the
formation of two CÀC bonds in just one synthetic operation,
affording a complex fused-bicyclic structure with boryl and
silyl groups and two non-conjugated double bonds. Control
experiments show that the reaction does not take place in the
absence of Ni(cod)2 or PCy3.
The scope of the reaction was evaluated under the opti-
mized reaction conditions (Table 1). Several 1,6-enynes with
both aryl and alkyl-substituted alkynes effectively performed
the carboborylative cyclization reaction (see Supporting Infor-
mation for enynes that failed to give the reaction). The best re-
sults were obtained with enynes containing simple alkyl tether-
ing chains (3a–c) bearing different substituents in the aromatic
ring in para position (Me and F). Nitrogen- and malonate-teth-
ered substrates also gave the desired products in good yields
(3e,f), albeit worse results were obtained for the oxygen deriv-
ative 3h and for the preparation of lactam 3i. The structure of
3i was confirmed by single-crystal X-ray crystallography (see
Crystallographic data for details). Interestingly, these com-
pounds, which present two stereogenic centers in the posi-
tions 1 and 4, are formed as single diastereoisomers, which
suggests a highly stereoselective reaction mechanism. Sub-
strates containing internal alkynes with different distal sub-
stituents, such as Me, Et and Bu, led to the desired products in
poor to excellent yields (3d, 3j–m) regardless of the enyne
connector. It is noteworthy that the longer chain (Bu) deriva-
tive affords lower yield in comparison with the ethyl-substitut-
ed analogue (22% for 3m vs. 99% for 3l). Enyne 1n, bearing a
terminal alkyne in the structure gave the reaction in moderate
yield (3n). An internal alkene was also evaluated, affording the
expected compound 3o, albeit in low yield. This method could
be also extended to a 1,7-enyne, leading to the formation of
two fused 6-membered rings in moderate yield (3p). Finally,
substitution in the allylic and propargylic positions was evalu-
[a] Conditions: enyne 1 (0.4 mmol) was slowly added by syringe pump
for 1 h to
a mixture of Ni(cod)2 (5 mol%), PCy3 (20 mol%) and 2
(1.1 equiv) in toluene (2 mL) at 808C. [b] Isolated yields. [c] We could not
assign the crystal structure to the major or minor isomers.
ated. Thus, enynes 1q and 1r afforded the corresponding
compounds 3q and 3r, respectively, in good yields as diaste-
reomeric mixtures. Again, compound 3r was successfully crys-
tallized, which allowed the confirmation of the proposed struc-
ture for the fused-bicycle.
Noticeably, enyne 1g, bearing a p-CN substituent on the aryl
ring, exclusively afforded the conjugated 1,3-diene 3g in high
yield. In fact, we have observed that compounds 3 are not
very stable and tend to evolve through different pathways, in-
volving aromatization and deborylative-aromatization of the 6-
membered ring, which made difficult their purification and
characterization. However, it was possible to identify and char-
acterize some of these products such as 3a’ and 3 f’ (Figure 1).
The latter was obtained when we tried to crystallize com-
pound 3 f under air. Formation of compound 3 f’ involves de-
&
&
Chem. Eur. J. 2019, 25, 1 – 6
www.chemeurj.org
2
ꢂ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
alkyne moieties seem to be incorporated, we observed the for-
mation of complex mixtures of several isomers as well as de-
composition products.
With the aim of getting preliminary insight into the reaction
mechanism, and to propose a reasonable pathway for the for-
mation of compounds 3, additional experiments were per-
formed (Scheme 3).
Figure 1. Compounds isolated after decomposition.
borylation (probably by hydrolysis) followed by 1,2-migration
of TMS. This process has been previously reported in other ar-
ylsilanes, and it is proposed to take place through a cationic
pathway triggered by protonation of the aromatic ring, which
is favored by the stabilizing effect of Si, and driven by the re-
lease of steric hindrance.[12]
In contrast to the reactivity observed for the enynes shown
above, the reaction of enones 1s and 1t under similar condi-
tions led to cyclic ketones 5a and 5b, respectively, in which
only the alkyne moiety from the alkynylboronate was incorpo-
rated to the structure (Scheme 2). Although we have no exper-
Scheme 3. Essays to probe the reaction pathway.
Thus, we tested our optimal reaction conditions with simple
alkynes and alkenes (Scheme 3a). When we used 4-octyne as
substrate, the previously described carboborylation com-
pound 6 was obtained. Surprisingly, when styrene was em-
ployed, borylated compound 7 was obtained in moderate
yield. Both results are consistent with an initial CÀB bond acti-
vation. On the other hand, terminal alkynes such as phenylace-
tylene and ethynyltrimethylsilane (lacking the boryl group)
only afforded oligomerization products (see Supporting Infor-
mation for details). To evaluate the feasibility of an oxidative
cyclometalation on a dicoordinated enyne, stoichiometric reac-
tion between Ni(cod)2, PCy3 and enyne 1a, without alkynylbor-
onate, was performed. After hydrolyzing the reaction mixture
with DCl·D2O, the expected dideuterated cyclic compound was
not detected, and only oligomerization of enyne was observed
(Scheme 3b). Therefore, oxidative cyclometalation involving
both CÀC multiple bonds of the enyne does not seem to take
place under the reaction conditions.
Scheme 2. Ni-catalyzed carbocyclization of enones, and possible reaction
pathway.
imental evidence, formation of compounds 5 might take place
by generation of a Ni-enolate complex, followed by transmeta-
lation of alkynyl to the metal, insertion of the alkyne into the
alkynylÀNi bond and reductive elimination.[13] An alternative in-
itial CÀB bond activation, two subsequent consecutive inser-
tions of the alkyne and alkene, and a final hydrolysis of an in-
termediate boron enolate during the reaction work-up would
also explain these structures. Nevertheless, CÀB oxidative addi-
tion to Ni is not probably operating in this case (see below).[11]
We tried to extend the reaction to other alkynylboronates,
bearing Ph, p-Tol or n-Hex instead of TMS group. Unfortunately,
the desired products were not obtained. Although boron and
In addition, the catalytic system in the absence of the enyne
was also studied by 31P- and 11B-NMR. Comparison of the 31P-
NMR spectrum of a mixture of Ni/PCy3 (1:4) in [D8]toluene with
that of a mixture of Ni/PCy3/2 (1:4:1) stirred at 808C for 5 mi-
nutes, indicated the formation of a new species showing a
signal at 20.7 ppm. The same signal was observed when the
mixture was stirred at 238C for 2 h. On the other hand, the 11B-
NMR spectrum of a mixture of Ni/PCy3/2 (1:2:1) stirred for
10 min at 238C, showed two signals at 21.9 and 29.5 ppm, and
unreacted alkynylboronate 2 (23.5 ppm). When heating this so-
lution for 10 min at 808C, only the signal at 21.9 ppm was ob-
Chem. Eur. J. 2019, 25, 1 – 6
www.chemeurj.org
3
ꢂ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
served (see Supporting Information for details). These results
suggest that the alkyne interacts with the precatalyst affording
a new species, but the small shift observed is probably due to
alkyne coordination rather than oxidative addition of the CÀB
to Ni0, which was proposed for the alkynylborylation of alky-
nes.[8d]
CÀB bond to Ni0, which drives the observed reaction outcome.
Consequently, no carboborylation of enynes takes place, in
contrast to the reactivity observed for simple alkynes under
similar conditions.
Finally, we synthetized the dideuterated enyne 1a–d2
(72%D incorporation) in the terminal position of the alkene.
The carboborylative cyclization reaction under the optimized
conditions led to compound 3a–d2 in 80% yield with the ex-
pected deuterium distribution (Scheme 5). This result is in
accord with the mechanistic proposal.
The formation of non-conjugated cyclic dienes from the re-
action substrates is intriguing for a reaction taking place at
808C. For this reason, the thermodynamic stability of some of
the observed reaction products (3c, 3g, and 3l), compared
with the corresponding conjugated dienes, was studied com-
putationally at DFT level. Interestingly, the observed 1,4-dienes
are more stable (5 to 8 kcalmolÀ1 in terms of DG, M06/6-
31G(d)), probably due to the release, upon deconjugation, of
the high steric strain that exists in the conjugated diene be-
tween the coplanar SiMe3, Bpin, and the substituent of the
alkyne.
The above-mentioned experiments lead to disregard both
the oxidative addition of CÀB bond to Ni, and the formation of
a nickelacyclopentadiene by oxidative cyclometalation of the
coordinated enyne. Instead, we propose an initial oxidative cy-
clometalation involving the alkyne groups present in 2 and the
enyne, after previous coordination to Ni0 (Scheme 4). The re-
Scheme 5. Deuterium migration.
In conclusion, we have described the Ni-catalyzed cyclization
reaction of enynes with alkynylboronates. The reaction condi-
tions involve a simple as well as non-expensive catalytic
system, and short reaction times are required to obtain good
to quantitative yields. From simple structures, such as enynes
and alkynylboronates, we could obtain complex fused-bicyclic
structures with two non-conjugated double bonds in the struc-
ture in a complete atom-economical fashion. The reaction tol-
erates several functional groups affording the desired com-
pounds in high yields. In addition, the structure contains two
reactive groups, Bpin and TMS, which may be used for further
transformations. Extension to other functionalized alkynes
should be interesting. We have contributed to the develop-
ment of a novel synthetic methodology, which extends the or-
ganic chemistry toolbox for the preparation of complex mole-
cules.
Experimental Section
Scheme 4. Proposed reaction pathway.
X-ray crystallographic data
CCDC 1906092 (3i), 1906093 (3r) and 1906094 (3 f’) contain the
supplementary crystallographic data for this paper. These data are
provided free of charge by The Cambridge Crystallographic Data
Centre.
sulting nickelacyclopentadiene would evolve by carbometala-
tion of the alkene and subsequent reductive elimination to
afford a 1,3-diene and regenerating the Ni0 species. In fact, we
could isolate such kind of derivative in one case (3g, Table 1).
An off-cycle isomerization process involving a 1,3- hydrogen
migration would lead to the observed products. We have no
explanation for the lack of isomerization of 3g. Thus, this reac-
tion cannot be considered a borylative carbocyclization, but a
cycloaddition involving three multiple CÀC bonds. Related
Fe-,[14] and Fe-catalyzed[15] processes have been previously de-
scribed for the formation of pyridines and other cyclic deriva-
tives. Although further studies are necessary to ascertain the
reaction mechanism, our experimental results indicate that, no-
ticeably, the oxidative cyclometalation involving two different
alkynes seems to be faster than the oxidative addition of the
Acknowledgements
We thank the Spanish MINECO for funding (Grant CTQ2016-
79826-R) and a Juan de la Cierva fellowship to M. T. Q., the
MECD for an FPU fellowship to N. C.-L., the Centro de Computa-
ciꢀn Cientꢂfica-UAM.
&
&
Chem. Eur. J. 2019, 25, 1 – 6
www.chemeurj.org
4
ꢂ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
g) I. Kageyuki, I. Osaka, K. Takaki, H. Yoshida, Org. Lett. 2017, 19, 830–
833; h) K. M. Logan, K. B. Smith, M. K. Brown, Angew. Chem. Int. Ed.
2015, 54, 5228–5231; Angew. Chem. 2015, 127, 5317–5320; i) Y. D.
Bidal, F. Lazreg, C. S. J. Cazin, ACS Catal. 2014, 4, 1564–1569; j) K. B.
Smith, K. M. Logan, W. You, M. K. Brown, Chem. Eur. J. 2014, 20, 12032–
12036; k) Y. Zhou, W. You, K. B. Smith, M. K. Brown, Angew. Chem. Int. Ed.
2014, 53, 3475–3479; Angew. Chem. 2014, 126, 3543–3547; l) H. Yoshi-
da, I. Kageyuki, K. Takaki, Org. Lett. 2013, 15, 952–955; m) R. Alfaro, A.
Parra, J. Alemꢁn, J. L. Garcꢄa Ruano, M. Tortosa, J. Am. Chem. Soc. 2012,
134, 15165–15168. For Reviews, see: n) E. Rivera-Chao, L. Fra, M.
FaÇanꢁs-Mastral, Synthesis 2018, 50, 3825–3832; o) G. Kehr, G. Erker,
Chem. Sci. 2016, 7, 56–65; p) G. Kehr, G. Erker, Chem. Commun. 2012,
48, 1839–1850; q) M. Suginome, Chem. Rec. 2010, 10, 348–358.
[9] Pd-catalyzed: a) A. Martos-Redruejo, R. Lꢀpez-Durꢁn, E. BuÇuel, D. J.
Cꢁrdenas, Chem. Commun. 2014, 50, 10094–10097; b) R. Lꢀpez-Durꢁn,
A. Martos-Redruejo, E. BuÇuel, V. Pardo-Rodrꢄguez, D. J. Cꢁrdenas, Chem.
Commun. 2013, 49, 10691–10693; c) V. Pardo-Rodrꢄguez, E. BuÇuel, D.
Collado-Sanz, D. J. Cꢁrdenas, Chem. Commun. 2012, 48, 10517–10519;
d) J. Marco-Martꢄnez, E. BuÇuel, R. Lꢀpez-Duran, D. J. Cꢁrdenas, Chem.
Eur. J. 2011, 17, 2734–2741; e) V. Pardo-Rodrꢄguez, J. Marco-Martꢄnez, E.
BuÇuel, D. J. Cꢁrdenas, Org. Lett. 2009, 11, 4548–4551; f) J. Marco-Martꢄ-
nez, E. BuÇuel, R. MuÇoz-Rodrꢄguez, D. J. Cꢁrdenas, Org. Lett. 2008, 10,
3619–3621; g) J. Marco-Martꢄnez, V. Lꢀpez-Carrillo, E. BuÇuel, R. Siman-
cas, D. J. Cꢁrdenas, J. Am. Chem. Soc. 2007, 129, 1874–1875. For Re-
views, see: h) E. BuÇuel, D. J. Cꢁrdenas, Chem. Eur. J. 2018, 24, 11239–
11244; i) E. BuÇuel, D. J. Cꢁrdenas, Eur. J. Org. Chem. 2016, 5446–5464.
[10] N. Cabrera-Lobera, P. Rodrꢄguez-Salamanca, J. C. Nieto-Carmona, E.
BuÇuel, D. J. Cꢁrdenas, Chem. Eur. J. 2018, 24, 784–788.
Conflict of interest
The authors declare no conflict of interest.
Keywords: boron · carbocycles · homogeneous catalysis ·
nickel · reaction mechanism
[1] R. A. Sheldon, I. W. C. E. Arends, U. Hanefeld, Green Chemistry and Catal-
ysis, Wiley-VCH, Weinheim, 2007.
[2] a) J. E. Zweig, D. E. Kim, T. R. Newhouse, Chem. Rev. 2017, 117, 11680–
11752; b) Md. S. Hossain, P. K. Roy, R. Ali, C. M. Zakaria, Md. Kudrat-E-
Zahan, Clin. Med. Res. 2017, 6, 177–191; c) J. McCleverty, Chemistry of
the First Row Transition Metals, Oxford Chemistry Primers, 1999.
[3] a) J. Carreras, A. Caballero, P. J. Pꢃrez, Chem. Asian J. 2019, 14, 329–343;
b) Synthesis and Application of Organoboron Compounds, (Eds.: E.
Fernꢁndez, A. Whiting), Springer, Switzerland, 2015, 49; c) D. G. Hall in
Boronic Acids: Preparation and Applications in Organic Synthesis Medicine
and Materials, Vol. 2, (Ed.: D. G. Hall), Wiley-VCH, Weinheim, 2011; d) W.
Yang, X. Gao, B. Wang, Med. Res. Rev. 2003, 23, 346–368.
[4] a) S. E. Hooshmand, B. Heidari, R. Sedghi, R. S. Varma, Green Chem.
2019, 21, 381–405; b) N. Miyaura, Top. Curr. Chem. 2002, 219, 11–59;
c) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–2483.
[5] a) T. Koolmeister, M. Sçdergren, M. Scobie, Tetrahedron Lett. 2002, 43,
5965–5968; b) N. A. Petasis, I. A. Zavialov, J. Am. Chem. Soc. 1997, 119,
445–446; c) N. A. Petasis, I. Akritopouiou, Tetrahedron Lett. 1993, 34,
583–586.
[11] N. Cabrera-Lobera, M. T. Quirꢀs, E. BuÇuel, D. J. Cꢁrdenas, Catal. Sci.
Technol. 2019, 9, 1021–1029.
[6] Selected Reviews: a) J. F. Hartwig, Chem. Soc. Rev. 2011, 40, 1992–2002;
b) I. A. I. Mkhalid, J. H. Barnard, T. B. Marder, J. M. Murphy, J. F. Hartwig,
Chem. Rev. 2010, 110, 890–931; c) A.-M. Carroll, T. P. O’Sullivan, P. J.
Guiry, Adv. Synth. Catal. 2005, 347, 609–631; d) C. M. Vogels, S. A. West-
cott, Curr. Org. Chem. 2005, 9, 687–699; e) C. M. Crudden, D. Edwards,
Eur. J. Org. Chem. 2003, 4695–4712.
[7] Selected Reviews: a) J. Royes, A. B. Cuenca, E. Fernꢁndez, Eur. J. Org.
Chem. 2018, 2728–2739; b) F. Zhao, X. Jia, P. Li, J. Zhao, Y. Zhou, J.
Wang, H. Liu, Org. Chem. Front. 2017, 4, 2235–2255; c) J. Takaya, N. Iwa-
sawa, ACS Catal. 2012, 2, 1993–2006; d) J. Ramꢄrez, V. Lillo, A. M. Segar-
ra, E. Fernꢁndez, C. R. Chimie 2007, 10, 138–151.
[8] Fe-catalyzed: a) N. Nakagawa, T. Hatakeyama, M. Nakamura, Chem. Eur.
J. 2015, 21, 4257–4261. Ni-catalyzed: b) K. M. Logan, S. R. Sardini, S. D.
White, M. K. Brown, J. Am. Chem. Soc. 2018, 140, 159–162; c) M. Daini,
A. Yamamoto, M. Suginome, Asian J. Org. Chem. 2013, 2, 968–976;
d) M. Suginome, M. Shirakura, A. Yamamoto, J. Am. Chem. Soc. 2006,
128, 14438–14439; e) E. Shirakawa, G. Takahashi, T. Tsuchimoto, Y. Kawa-
kami, Chem. Commun. 2001, 2688–2689. Cu- or Cu/Pd-catalyzed: f) B.
Chen, P. Cao, Y. Liao, M. Wang, J. Liao, Org. Lett. 2018, 20, 1346–1349;
[12] a) T. Shimizu, S. Morisako, Y. Yamamoto, A. Kawachi, Heteroat. Chem.
2018, 29, e21434; b) B. Becker, A. Herman, W. Wojnowski, J. Organomet.
Chem. 1980, 193, 293–297; c) D. Seyferth, S. C. Vick, J. Organomet.
Chem. 1977, 141, 173–187; d) D. Seyferth, D. L. White, J. Am. Chem. Soc.
1972, 94, 3132–3138.
[13] S. Ikeda, Y. Sato, J. Am. Chem. Soc. 1994, 116, 5975–5976.
[14] B. R. D’Souza, T. K. Lane, J. Louie, Org. Lett. 2011, 13, 2936–2939.
[15] a) A. Thakur, J. Louie, Acc. Chem. Res. 2015, 48, 2354–2365; b) T. N. Teka-
vec, G. Zuo, K. Simon, J. Org. Chem. 2006, 71, 5834–5836; c) M. M. Mc-
Cormick, H. A. Duong, G. Zuo, J. Louie, J. Am. Chem. Soc. 2005, 127,
5030–5031; d) J. Louie, J. E. Gibby, M. V. Farnworth, T. N. Tekavec, J. Am.
Chem. Soc. 2002, 124, 15188–15189.
Manuscript received: July 25, 2019
Accepted manuscript online: September 13, 2019
Version of record online: && &&, 0000
Chem. Eur. J. 2019, 25, 1 – 6
www.chemeurj.org
5
ꢂ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
COMMUNICATION
&
Nickel Catalysis
N. Cabrera-Lobera, M. T. Quirꢀs,
E. BuÇuel,* D. J. Cꢁrdenas*
&& – &&
Ni-Catalyzed Cyclization of Enynes
and Alkynylboronates:
Boryl-1,4-dienes: Ni-catalyzed carbo-
borylative cyclization reaction of enynes
with alkynylboronates affords complex
fused-bicyclic compounds containing
borylated 1,4-cyclohexadienes. The pro-
cess is fully atom-economical, and the
catalytic system employs simple and in-
expensive Ni salt and phosphine-based
ligand.
Atom-Economical Synthesis of Boryl-
1,4-dienes
&
&
Chem. Eur. J. 2019, 25, 1 – 6
www.chemeurj.org
6
ꢂ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!