Palladium(II)-Catalyzed Oxidative Decarboxylative [2 + 2 + 1] Annulation of Cinnamic Acids with Alkynes: Access to Polysubstituted Pentafulvenes

Article abstract of DOI:10.1021/acs.orglett.0c01955

An unprecedented palladium(II)-catalyzed oxidative decarboxylative [2 + 2 + 1] annulation of cinnamic acids with alkynes has been developed for the synthesis of polysubstituted pentafulvenes. Ag2CO3 and DMSO are essential for the reaction. This protocol features readily available starting materials, a wide substrate scope, and moderate to excellent yields. Moreover, various significant frameworks can be easily obtained from the late-stage transformations of pentafulvenes via oxidation, reduction, and Scholl-type reaction.

Full text of DOI:10.1021/acs.orglett.0c01955

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Letter
Palladium(II)-Catalyzed Oxidative Decarboxylative [2 + 2 + 1]
Annulation of Cinnamic Acids with Alkynes: Access to
Polysubstituted Pentafulvenes
Shiyong Peng,* Nuan Chen, Hong Zhang, Min He, Hongguang Li, Ming Lang, and Jian Wang*
Cite This: https://dx.doi.org/10.1021/acs.orglett.0c01955
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ABSTRACT: An unprecedented palladium(II)-catalyzed oxidative
decarboxylative [2 + 2 + 1] annulation of cinnamic acids with
alkynes has been developed for the synthesis of polysubstituted
pentafulvenes. Ag2CO3 and DMSO are essential for the reaction.
This protocol features readily available starting materials, a wide
substrate scope, and moderate to excellent yields. Moreover,
various significant frameworks can be easily obtained from the late-
stage transformations of pentafulvenes via oxidation, reduction, and
Scholl-type reaction.
Scheme 1. Previous Reports and Our Proposal
ulvenes represent a fascinating class of organic compounds
Fand display a unique π-electron system predicated by their
cyclic cross-conjugated disposition.1 Among them, pentaful-
venes, well-known isomers of benzene with nonbenzenoid
aromaticity and high polarizability, are a unique class of
fulvenes that attracted much attention from synthetic chemists
due to their rich reactivities and wide applications in various
fields.2−6 Developing efficient and versatile routes toward
pentafulvenes is therefore highly desirable.
The conventional method for pentafulvenes is the
condensation of cyclopentadienes with carbonyl compounds,
which was quite limited because of the difficulties on the
synthesis of cyclopentadienes.7 Compared with the traditional
strategy, the alternative transition-metal-catalyzed [2 + 2 + 1]
homo- or cross-cyclotrimerization of alkynes or alkenes with
alkynes is a more efficient method that enables the diversity-
oriented synthesis of multisubstituted pentafulvenes.8−14
In particular, a few palladium-catalyzed [2 + 2 + 1]
annulations of alkenes with alkynes have been developed for
constructing pentafulvenes.11,12 As early as 1990, Lee and co-
workers discovered a palladium(0)-catalyzed [2 + 2 + 1]
coupling of haloalkenes with alkynes to synthesize 1,3,6-
trisubstituted pentafulvenes;11a following this pioneering work,
the groups of Heck,11b Takahashi,11c Miura,11d,e,g and Duan11f
successively reported similar reactions (Scheme 1a). In
contrast with the palladium(0)-catalyzed approach using
haloalkenes, recently, Gogoi and co-workers reported an
intriguing palladium(II)-catalyzed amide-directed [2 + 2 + 1]
annulation of 1,1-diaryl-alkenes with alkynes through the
vinylic geminal double C−H bond activation, offering a more
efficient synthetic approach to pentafulvenes (Scheme 1b).12a
However, an amide directing group is necessary, and styrenes
are prone to be polymerized. With the recent progress of
Received: June 10, 2020
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© XXXX American Chemical Society
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alkenyl acids in decarboxylative reactions,15 we envisioned that
cinnamic acids could act as readily available and stable
surrogates for the unstable styrenes via a palladium(II)-
catalyzed in situ decarboxylation and, thus, effect a possible [2
+ 2 + 1] annulation with alkynes (Scheme 1c). A formidable
challenge for this proposal is the well-documented competitive
transition-metal-catalyzed oxidative [4 + 2] annulation path-
way to produce α-pyrones.16,17
Based on the hypothesis and in continuation with our
interest in palladium(II)-catalyzed alkyne annulations for
developing novel methodologies to construct (hetero)-
carbocycles,18 herein, we report an unprecedented palladium-
(II)-catalyzed oxidative decarboxylative [2 + 2 + 1] annulation
of cinnamic acids with alkynes, selectively providing the
cyclotrimerization pentafulvenes in moderate to excellent
yields.
palladium(II) catalysts were evaluated, and the yield was
increased to 48% when Pd(TFA)2 was employed (entries 11−
13). To our delight, the yield was further increased to 65%
when 5% DMSO was added (entry 14). However, a higher
concentration of DMSO, as well as other additives such as
PPh3 and 2,4,6-collidine, was not effective (entries 15−17).
These results are consistent with related reports that DMSO is
a good ligand and facilitates the decarboxylation step, while
phosphine and pyridine ligands retard this process.19 More-
over, an increased temperature did not significantly improve
the yield, and a lower temperature was detrimental (entries 18
and 19). A decrease of the catalyst loading for the reaction
gave product 3aa in 58% yield with a longer reaction time
(entry 20).
With the optimal reaction conditions in hand, we next set
out to investigate the scope of cinnamic acids (Scheme 2). The
We commenced optimization of the reaction using cinnamic
acid 1a and diphenylacetylene 2a as model substrates (Table
1). After extensive investigations, the desired pentafulvene 3aa
a
Scheme 2. Scope of Cinnamic Acids
a
Table 1. Optimization of Reaction Conditions
b
entry
catalyst
oxidant
solvent
DMF
yield (%)
1
2
3
4
5
6
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(TFA)2
PdCl2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Ag2CO3
Ag2O
AgOAc
Cu(OAc)2
O2
24
−
−
<10
−
−
−
−
−
15
26
48
32
65
20
54
37
64
23
58
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
toluene
1,4-dioxane
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
K2S2O8
AgOAc
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
c
7
8
9
10
11
d
12
13
14
15
16
17
18
19
20
e
f
g
h
i
j
k
a
Reaction conditions: 1a (0.2 mmol), 2a (0.5 mmol), catalyst (10
mol %), oxidant (0.6 mmol), solvent (2.0 mL), 130 °C, 24 h, N2.
a
Reaction conditions: 1 (0.2 mmol), 2a (0.5 mmol), Pd(TFA)2 (10
mol %), Ag2CO3 (0.6 mmol), 5% DMSO/DMF (2.0 mL), 130 °C, 24
b
c
d
Isolated yields. K2CO3 (0.6 mmol). Pd(OAc)2 (20 mol %).
b
h, N2. Isolated yields. 3 mmol scale.
e
f
g
h
DMSO (0.1 mL). DMSO (0.5 mL). PPh3 (0.04 mmol). 2,4,6-
i
j
k
Collidine (0.04 mmol). At 150 °C. At 100 °C. Pd(TFA)2 (5 mol
%), 48 h.
reaction of diphenylacetylene 2a with different cinnamic acids
bearing electron-donating or electron-withdrawing substituents
at the aryl moiety all proceeded smoothly to afford the desired
products in moderate to excellent yields (3aa−ia). In general,
electron-rich cinnamic acids gave better results. Additionally,
cinnamic acids with different di- or trisubstituents at the aryl
moiety, and bulky 3-(naphthalen-1-yl)acrylic acid were also
well tolerated for the reaction (3ja−pa). Importantly, various
heteroaryl-derived cinnamic acids including furan, benzofuran,
benzothiophene, and indole rings were all compatible for this
reaction and afforded the corresponding pentafulvenes in
was obtained in 24% yield at 130 °C with Pd(OAc)2 as the
catalyst, Ag2CO3 as the oxidant, and N,N-dimethylformamide
(DMF) as the solvent (entry 1). Screening of different oxidants
revealed that Ag2CO3 was the best choice for this reaction
(entries 2−7). Next, different solvents were tested. DMF was
better than other solvents such as dimethyl sulfoxide (DMSO),
toluene, and 1,4-dioxane (entries 8−10). Because an increased
amount of Pd(OAc)2 did not improve the yield of 3aa, other
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moderate to good yields (3qa−ta), which may be promising
organic molecules for material science by introducing
heterocyclic aromatics.5,6 Unfortunately, crotonic acid as well
as 5-phenylpenta-2,4-dienoic acid was not suitable for the
reaction.
complete chemo-, regio-, and stereoselectivities, which should
be attributed to the silver(I)-catalyzed hydrocarboxylation.20
To further understand this decarboxylative annulation
process, two competition experiments were conducted
(Scheme 4). Electron-donating cinnamic acid 1b (R = OMe)
Next, various symmetric and unsymmetric diarylacetylenes
were subjected to this reaction (Scheme 3). Various symmetric
Scheme 4. Competition Experiments
a
Scheme 3. Scope of Alkynes
reacted more quickly than the electron-withdrawing cinnamic
acid 1f (R = F) (Scheme 4a). Similarly, electron-rich alkyne 2b
(R = 4-Me-Ph) reacted more efficiently than the electron-
deficient alkyne 2d (R = 4-F-Ph), providing inseperable
mixtures of 3bb/3bd together with the cross-annulated
products 3bb′/3bd′ (Scheme 4b).
On the basis of related palladium(II)-catalyzed oxidative
decarboxylation investigations15,19,21 and control experiments
(see Supporting Information), a plausible mechanism is
proposed (Scheme 5). The catalytic cycle would be initiated
Scheme 5. Proposed Reaction Mechanism
a
Reaction conditions: 1a−c (0.2 mmol), 2 (0.5 mmol), Pd(TFA)2
(10 mol %), Ag2CO3 (0.6 mmol), 5% DMSO/DMF (2.0 mL), 130
b
°C, 24 h, N2. Isolated yields. Determined by 1H NMR.
c
[Cp*RhCl2]2 (2.5 mol %) instead of Pd(TFA)2 (10 mol %).
alkynes with electron-donating or electron-withdrawing func-
tional groups efficiently converted to the corresponding
products in good yields. The unsymmetric diarylacetylenes
explored also delivered the desired pentafulvenes although as
inseperable mixtures of regioisomers (3bh−bi). Besides
diarylacetylenes, further experiments were also conducted
with commercially available dibutylacetylene 2j, diethylacety-
lene dicarboxylate 2k, and methyl 3-phenylpropiolate 2l.
However, no corresponding pentafulvenes were detected
under the optimal reaction conditions. Instead, when
[Cp*RhCl2]2 was employed as the catalyst instead of
Pd(TFA)2 under otherwise the same reaction conditions, the
α-pyrone 4aj from dibutylacetylene 2j was obtained, which was
consistent with the rhodium(III)-catalyzed oxidative [4 + 2]
cycloaddition reaction;17b−e enol esters 5ak and 5al from
electron-deficient alkynes 2k and 2l were isolated with
by the decarboxylation of cinnamic acid 1a in the presence of
Ag2CO3 as a base to give vinyl palladium intermediate I.22 The
subsequent successive carbopalladation of two alkynes 2a
affords trivinylpalladium species III, which then undergoes an
intramolecular Heck-type reaction leading to a palladacycle IV
followed by reductive elimination to afford product 3aa and
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palladium(0). Finally, palladium(0) is reoxidized to palladium-
(II) by the Ag2CO3 as an oxidant, thus closing the catalytic
cycle. However, the silver-promoted palladium cation pathway
could not be totally excluded.11c
Although several methods including our strategy for the
synthesis of 3aa have been well developed, there are rare
reports of its late-stage transformations.22 This prompted us to
further explore the transformations of 3aa under different
reaction conditions (Scheme 6). The product 3aa smoothly
tion chemistry as well as fulvene chemistry. Further studies will
be reported in due course.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01955.
Experimental procedures along with characterizing data,
copies of NMR spectra, and single crystal X-ray
structures (PDF)
a
Scheme 6. Transformations of 3aa
Accession Codes
CCDC 1024208−1024210 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
Shiyong Peng − School of Biotechnology and Health Sciences,
Wuyi University, Jiangmen 529020, P. R. China; orcid.org/
0000-0002-2387-5868; Email: psy880124@
a
Reaction conditions: (a) 3aa (0.1 mmol), m-CPBA (0.2 mmol),
DCM (2.0 mL), rt, 4 h. (b) 3aa (0.1 mmol), LiAlH4 (0.2 mmol),
Et2O (4.0 mL), 0 °C, 0.5 h; then quenching with H2O. (c) 3aa (0.1
mmol), DDQ (0.6 mmol), TfOH (0.6 mmol), DCM (4.0 mL), 0 °C
to rt, 21 h.
mail.nankai.edu.cn
Jian Wang − School of Biotechnology and Health Sciences, Wuyi
University, Jiangmen 529020, P. R. China; School of
Pharmaceutical Sciences, Key Laboratory of Bioorganic
Phosphorous Chemistry & Chemical Biology (Ministry of
Education), Tsinghua University, Beijing 100084, P. R. China;
orcid.org/0000-0002-3298-6367; Email: wangjian2012@
tsinghua.edu.cn
transformed to a conjugated 1,5-dione product 6 in 90% yield
through the exclusive endocyclic double bond cleavage by the
oxidation of m-CPBA in dichloromethane (DCM) at room
temperature (Scheme 6a). To the best of our knowledge, this
is the first example of the endocyclic double bond cleavage of
pentafulvenes.2a,23 Treatment of 3aa with LiAlH4 in diethyl
ether (Et2O) at 0 °C followed by quenching with water
furnished a densely functionalized 3-cyclopentenone scaffold 7
with a quaternary carbon center in 63% yield (Scheme 6b). We
envisioned that a Scholl intramolecular cyclization should be
possible due to the five adjacent phenyl substituents. Under
DDQ/TfOH systems in DCM at 0 °C to room temperature,
3aa was converted through a Scholl-type reaction to an
interesting polycyclic coumarin derivative 8 with a quaternary
carbon center in 58% yield (Scheme 6c).24 The structures of
compounds 6−8 were all unambiguously confirmed by X-ray
diffraction analysis (CCDC 1024210 for 6, CCDC 1024209
for 7, and CCDC 1024208 for 8).
Authors
Nuan Chen − School of Biotechnology and Health Sciences,
Wuyi University, Jiangmen 529020, P. R. China
Hong Zhang − School of Biotechnology and Health Sciences,
Wuyi University, Jiangmen 529020, P. R. China
Min He − School of Biotechnology and Health Sciences, Wuyi
University, Jiangmen 529020, P. R. China
Hongguang Li − School of Biotechnology and Health Sciences,
Wuyi University, Jiangmen 529020, P. R. China; orcid.org/
0000-0002-6579-7300
Ming Lang − School of Biotechnology and Health Sciences, Wuyi
University, Jiangmen 529020, P. R. China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01955
In summary, we have developed an unprecedented
palladium(II)-catalyzed oxidative decarboxylative [2 + 2 + 1]
annulation of cinnamic acids with alkynes, selectively
constructing functionalized pentafulvenes in moderate to
excellent yields. A featured advantage of this protocol is the
utilization of cinnamic acids as readily available and stable
substrates. Moreover, the pentafulvenes easily transform to
various significant structures through oxidation, reduction, and
Scholl-type reaction. Although this method is not currently
practical for large-scale synthesis due to the high loading of
silver salt required, the process is nonetheless of interest and
will enrich the fields of palladium(II)-catalyzed decarboxyla-
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are grateful for the financial support from the
Natural Science Foundation of Guangdong Province
(2018A030310680), the Research Foundation of Department
of Education of Guangdong Province (2018KTSCX236), and
the Science Foundation for Young Teachers of Wuyi
University (2019td09).
D
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A.; Nishikata, T.; Hagiwara, N.; Kawata, K.; Okeda, T.; Wang, H. F.;
Fugami, K.; Kosugi, M. Org. Lett. 2001, 3, 3313−3316.
REFERENCES
■
(1) For typical reviews on fulvenes, see: (a) Hopf, H. In Cross
Conjugation: Modern Dendralene, Radialene and Fulvene Chemistry;
Hopf, H., Sherburn, M. S., Eds.; Wiley: New York, 2016; pp 1−440.
(b) Finke, A. D.; Diederich, F. Chem. Rec. 2015, 15, 19−30.
(c) Neuenschwander, M. Helv. Chim. Acta 2015, 98, 731−762.
(d) Neuenschwander, M. Helv. Chim. Acta 2015, 98, 763−784.
(2) For a recent review on pentafulvenes, see: (a) Preethalayam, P.;
Krishnan, K. S.; Thulasi, S.; Chand, S. S.; Joseph, J.; Nair, V.;
Jaroschik, F.; Radhakrishnan, K. V. Chem. Rev. 2017, 117, 3930−
3989. For the substitution effects on the aromatic character of
(13) For other typical examples of transition-metal-catalyzed fulvene
syntheses, see: (a) Uemura, M.; Takayama, Y.; Sato, F. Org. Lett.
2004, 6, 5001−5004. (b) Brahim, M.; Ammar, H. B.; Dorcet, V.;
́
Soule, J.-F.; Doucet, H. Org. Lett. 2017, 19, 2584−2587. (c) Chen, Y.;
Liu, Y. J. Org. Chem. 2011, 76, 5274−5282.
(14) For selected examples of non-transition-metal mediated fulvene
syntheses, see: (a) Himeda, Y.; Yamataka, H.; Ueda, I.; Hatanaka, M.
J. Org. Chem. 1997, 62, 6529−6538. (b) Sinu, C. R.; Suresh, E.; Nair,
V. Org. Lett. 2013, 15, 6230−6233. (c) Xie, J.-W.; Xu, M.-L.; Zhang,
R.-Z.; Pan, J.-Y.; Zhu, W.-D. Adv. Synth. Catal. 2014, 356, 395−400.
(15) For a recent review on the decarboxylation reactions of alkenyl
acids, see: Kaur, P.; Kumar, V.; Kumar, R. Catal. Rev.: Sci. Eng. 2020,
62, 118−161.
́
pentafulvenes, see: (b) Krygowski, T. M.; Cyranski, M. K. Chem. Rev.
2001, 101, 1385−1419.
(3) For a review on bioactivity of pentafulvenes, see: (a) Strohfeldt,
K.; Tacke, M. Chem. Soc. Rev. 2008, 37, 1174−1187. For typical
examples, see: (b) MacDonald, J. R.; Muscoplat, C. C.; Dexter, D. L.;
Mangold, G. L.; Chen, S.-F.; Kelner, M. J.; McMorris, T. C.; Von
Hoff, D. D. Cancer Res. 1997, 57, 279−283. (c) Wang, Y.; Wiltshire,
T.; Senft, J.; Reed, E.; Wang, W. Biochem. Pharmacol. 2007, 73, 469−
480.
(16) For selected reviews, see: (a) Goel, A.; Ram, V. J. Tetrahedron
2009, 65, 7865−7913. (b) Pal, S.; Chatare, V.; Pal, M. Curr. Org.
Chem. 2011, 15, 782−800.
(17) For Pd(II)-catalysis, see: (a) Yu, Y.; Huang, L.; Wu, W.; Jiang,
H. Org. Lett. 2014, 16, 2146−2149. For Rh(III)-catalysis, see:
(b) Mochida, S.; Hirano, K.; Satoh, T.; Miura, M. J. Org. Chem. 2009,
74, 6295−6298. (c) Itoh, M.; Shimizu, M.; Hirano, K.; Satoh, T.;
Miura, M. J. Org. Chem. 2013, 78, 11427−11432. (d) Kudo, E.;
Shibata, Y.; Yamazaki, M.; Masutomi, K.; Miyauchi, Y.; Fukui, M.;
Sugiyama, H.; Uekusa, H.; Satoh, T.; Miura, M.; Tanaka, K. Chem. -
Eur. J. 2016, 22, 14190−14194. (e) Li, Y.-T.; Zhu, Y.; Tu, G.-L.;
Zhang, J.-Y.; Zhao, Y.-S. Chem. - Asian J. 2018, 13, 3281−3284. For
Ru(II)-catalysis, see: (f) Prakash, R.; Shekarrao, K.; Gogoi, S. Org.
Lett. 2015, 17, 5264−5267.
(4) For recent reviews on organometallic applications of
pentafulvenes, see: (a) Erker, G. Coord. Chem. Rev. 2006, 250,
1056−1070. (b) Gleiter, R.; Bleiholder, C.; Rominger, F. Organo-
metallics 2007, 26, 4850−4859. For recent examples, see: (c) Bader,
M.; Marquet, N.; Kirillov, E.; Roisnel, T.; Razavi, A.; Lhost, O.;
Carpentier, J.-F. Organometallics 2012, 31, 8375−8387. (d) Oswald,
T.; Gelert, T.; Lasar, C.; Schmidtmann, M.; Kluener, T.; Beckhaus, R.
Angew. Chem., Int. Ed. 2017, 56, 12297−12301.
(5) For examples on semiconductor applications of pentafulvenes,
see: (a) Aqad, E.; Leriche, P.; Mabon, G.; Gorgues, A.;
Khodorkovsky, V. Org. Lett. 2001, 3, 2329−2332. (b) Andrew, T.
L.; Cox, J. R.; Swager, T. M. Org. Lett. 2010, 12, 5302−5305.
(6) For a review on solar cell applications of pentafulvenes, see:
(a) An, Q.; Zhang, F.; Zhang, J.; Tang, W.; Deng, Z.; Hu, B. Energy
Environ. Sci. 2016, 9, 281−322. For an example, see: (b) Godman, N.
P.; Balaich, G. J.; Iacono, S. T. Chem. Commun. 2016, 52, 5242−5245.
(7) For typical examples, see: (a) Stone, K. J.; Little, R. D. J. Org.
(18) (a) Wang, L.; Peng, S.; Wang, J. Chem. Commun. 2011, 47,
5422−5424. (b) Wang, L.; Huang, J.; Peng, S.; Liu, H.; Jiang, X.;
Wang, J. Angew. Chem., Int. Ed. 2013, 52, 1768−1772. (c) Peng, S.;
Wang, L.; Wang, J. Chem. - Eur. J. 2013, 19, 13322−13327. (d) Peng,
S.; Wang, L.; Huang, J.; Sun, S.; Guo, H.; Wang, J. Adv. Synth. Catal.
2013, 355, 2550−2557. (e) Peng, S.; Gao, T.; Sun, S.; Peng, Y.; Wu,
M.; Guo, H.; Wang, J. Adv. Synth. Catal. 2014, 356, 319−324.
(f) Wang, L.; Du, Z.; Peng, S.; Zhang, K.; Wang, J. Adv. Synth. Catal.
2014, 356, 2943−2947. (g) Wang, L.; Zhang, J.; Lang, M.; Wang, J.
Org. Chem. Front. 2016, 3, 603−608. (h) Peng, S.; Sun, Z.; Zhu, H.;
Chen, N.; Sun, X.; Gong, X.; Wang, J.; Wang, L. Org. Lett. 2020, 22,
3200−3204.
(19) For the importance of DMSO in the Pd(II)-catalyzed oxidative
decarboxylation process, see: (a) Myers, A. G.; Tanaka, D.; Mannion,
M. R. J. Am. Chem. Soc. 2002, 124, 11250−11251. (b) Tanaka, D.;
Myers, A. G. Org. Lett. 2004, 6, 433−436. (c) Tanaka, D.; Romeril, S.
P.; Myers, A. G. J. Am. Chem. Soc. 2005, 127, 10323−10333.
(d) Wang, C.; Piel, I.; Glorius, F. J. Am. Chem. Soc. 2009, 131, 4194−
4195.
̈
Chem. 1984, 49, 1849−1853. (b) Erden, I.; Gartner, C. Tetrahedron
Lett. 2009, 50, 2381−2383. (c) Coskun, N.; Erden, I. Tetrahedron
̧
2011, 67, 8607−8614. (d) Peloquin, A. J.; Stone, R. L.; Avila, S. E.;
Rudico, E. R.; Horn, C. B.; Gardner, K. A.; Ball, D. W.; Johnson, J. E.
B.; Iacono, S. T.; Balaich, G. J. J. Org. Chem. 2012, 77, 6371−6376.
(8) For a Ti(IV)-catalyzed [2 + 2 + 1] homo-cyclotrimerization of
alkynes, see: Johnson, E. S.; Balaich, G. J.; Fanwick, P. E.; Rothwell, I.
P. J. Am. Chem. Soc. 1997, 119, 11086−11087.
(9) For a Pd(0)-catalyzed [2 + 2 + 1] homo-cyclotrimerization of
alkynes, see: Radhakrishnan, U.; Gevorgyan, V.; Yamamoto, Y.
Tetrahedron Lett. 2000, 41, 1971−1974.
(10) For a Rh(I)-catalyzed [2 + 2 + 1] cross-cyclotrimerization of
alkynes, see: (a) Shibata, Y.; Tanaka, K. Angew. Chem., Int. Ed. 2011,
50, 10917−10921. For a similar version of alkenes with alkynes, see:
(b) Yoshizaki, S.; Shibata, Y.; Tanaka, K. Angew. Chem., Int. Ed. 2017,
56, 3590−3593.
(20) For Ag(I)-catalyzed intermolecular addition of carboxylic acids
to alkynes, see: (a) Ishino, Y.; Nishiguchi, I.; Nakao, S.; Hirashima, T.
Chem. Lett. 1981, 10, 641−644. (b) Kikui, N.; Hinoue, T.; Usuki, Y.;
Satoh, T. Chem. Lett. 2018, 47, 141−143. For a related review, see:
(c) Alonso, F.; Beletskaya, I. P.; Yus, M. Chem. Rev. 2004, 104, 3079−
3159.
(11) For Pd(0)-catalyzed [2 + 2 + 1] cross-cyclotrimerizations of
haloalkenes with alkynes, see: (a) Lee, G. C. M.; Tobias, B.; Holmes,
J. M.; Harcourt, D. A.; Garst, M. E. J. Am. Chem. Soc. 1990, 112,
9330−9336. (b) Silverberg, L. J.; Wu, G.; Rheingold, A. L.; Heck, R.
F. J. Organomet. Chem. 1991, 409, 411−420. (c) Kotora, M.;
Matsumura, H.; Gao, G.; Takahashi, T. Org. Lett. 2001, 3, 3467−
3470. (d) Shibata, K.; Satoh, T.; Miura, M. Adv. Synth. Catal. 2007,
349, 2317−2325. (e) Horiguchi, H.; Hirano, K.; Satoh, T.; Miura, M.
Adv. Synth. Catal. 2009, 351, 1431−1436. (f) Huang, H.; Li, J.;
Lescop, C.; Duan, Z. Org. Lett. 2011, 13, 5252−5255. For a recent
similar process of in situ generated haloalkenes with alkynes, see:
(g) Suzuki, S.; Kinoshita, H.; Miura, K. Org. Lett. 2019, 21, 1612−
1616.
(21) (a) Rodríguez, N.; Goossen, L. J. Chem. Soc. Rev. 2011, 40,
5030−5048. (b) Wang, C.; Rakshit, S.; Glorius, F. J. Am. Chem. Soc.
2010, 132, 14006−14008.
(22) There are only two examples on the dipolar cycloaddition of
3aa, see: (a) Dhar, D. N.; Ragunathan, R. Tetrahedron 1984, 40,
1585−1590. (b) Saeki, T.; Toshimitsu, A.; Tamao, K. Silicon Chem.
2003, 2, 125−129.
(23) For an endocyclic epoxidation of pentafulvenes, see: Adam, W.;
Hadjiarapoglou, L. P.; Meffert, A. Tetrahedron Lett. 1991, 32, 6697−
6700.
(24) Jones, D. J.; Purushothaman, B.; Ji, S.; Holmes, A. B.; Wong, W.
W. H. Chem. Commun. 2012, 48, 8066−8088.
(12) For Pd(II)-catalyzed [2 + 2 + 1] cross-cyclotrimerizations of
alkenes with alkynes, see: (a) Phukon, J.; Gogoi, S. Chem. Commun.
2020, 56, 1133−1136. (b) Du, X.; Suguro, M.; Hirabayashi, K.; Mori,
E
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