Fused-Ring Formation by an Intramolecular “Cut-and-Sew” Reaction between Cyclobutanones and Alkynes

Article abstract of DOI:10.1002/anie.201712487

The development of a catalytic intramolecular “cut-and-sew” transformation between cyclobutanones and alkynes to construct cyclohexenone-fused rings is described herein. The challenge arises from the need for selective coupling at the more sterically hind

Full text of DOI:10.1002/anie.201712487

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Accepted Article
Title: Fused-Ring Formation via an Intramolecular "Cut-and-Sew"
Reaction between Cyclobutanones and Alkynes
Authors: Lin Deng, Likun Jin, and Guangbin Dong
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201712487
Angew. Chem. 10.1002/ange.201712487
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10.1002/anie.201712487
Angewandte Chemie International Edition
COMMUNICATION
Fused-Ring Formation via an Intramolecular “Cut-and-Sew”
Reaction between Cyclobutanones and Alkynes
Lin Deng, Likun Jin, and Guangbin Dong*
Abstract: Herein, we describe the development of a catalytic
intramolecular “cut-and-sew” transformation between
(Scheme 2b).[2g] In addition, decarbonylation of cyclobutanones
to form the corresponding cyclopropane byproduct is always a
major competing pathway.[2a,g,h] As illustrated in Scheme 2a,
directly forming rhodacycle A, the reactive intermediate for
subsequent 2π-insertion, is more difficult than rhodacycle B. One
cyclobutanones and alkynes to construct cyclohexenone-fused rings.
The challenge arises from the need for selective coupling at the
more sterically hindered proximal position, which can be addressed
using an electron-rich but less bulky phosphine ligand. The control
experiment and 13C-labelling study suggest that the reaction may
start with cleavage of the less hindered distal C−C bond of
cyclobutanones, followed by decarbonylation and CO reinsertion to
enable Rh insertion at the more hindered proximal position.
possible solution is to enable
a
facile and reversible
decarbonylation/reinsertion pathway,[4] in which rhodacyclo-
pentanone B can be converted first to a rhodacyclobutane
intermediate C and then to rhodacycle A via CO-reinsertion. We
anticipate that the choice of the ligand would be critical for this
transformation,
because
it
should
allow
efficient
decarbonylation/CO-reinsertion without promoting further
reductive elimination of C (an irreversible process to give
cyclopropanes, vide infra, Scheme 5a), which represents a main
difference from the prior benzocyclobutenone system.[5] Herein,
we disclose the development of an effective catalytic system for
fused-ring formation via an intramolecular “cut-and-sew” reaction
between cyclobutanones and alkynes (Scheme 3a).[6] The
transformation is enabled by use of an electron-rich, less bulky
phosphine ligand and an electron-deficient Rh precatalyst,
offering a rapid access to cyclohexenone-fused rings.
Transition metal (TM)-catalyzed carbon−carbon bond (C−C)
activation provides unique opportunities to develop various
intriguing transformations.[1] In particular, oxidative addition of
TM into C−C σ bonds followed by 2π-insertion, namely a “cut-
and-sew” process, has been demonstrated to be effective for
construction of complex ring scaffolds.[1r] Cyclobutanone
derivatives are of special interest for this type of transformations
due to their easy access from olefins and high reactivity towards
C−C activation.[1i,n,o,q,r] To date, significant progress has been
achieved for synthesis of bridged rings via intramolecular “cut-
and-sew” reactions, in which cyclobutanones are coupled with
an unsaturated unit tethered at the C3 position (Scheme 1a).[2]
However, using such a strategy to assemble fused-ring systems
remains an unmet challenge (Scheme 1b).[3]
Steric challenge
a)
O
O
proximal
distal
4
O
R
Rh
[Rh]
[Rh]
Rh
R
L
less favored
2
favored
B
A
R
CO
Rh
CO-reinsertion
CO-deinsertion
R
formation
a) Bridged-ring
C
less bulky
O
X
O
undesired
R
B
A
B
R'
R1
M
B
A
[M]
established
A
KEY:
between rhodacycles A
B
&
promoting
R'
equilibrium
R'
3
R
R
example
Previous
b)
O
Me
Me
Me
O
Me
Me
Me
O
Fused-ring formation
bulkier
b)
Me
Me
[Rh]
B
Me
+
Me
B
O
O
Ts
[ref. 2g]
N
A
B
O
N
N
A
?
Me
previously
unknown
M
[M]
A
Ts
Ts
35%
17%
2
R
R
R
Scheme 2. Challenges for fused-ring formation with cyclobutanones
Scheme 1. “Cut and sew” reactions with cyclobutanones
Of note, similar bicyclic structures could also be obtained
through a (3+2+1) cycloaddition reactions[4e,7] involving C−C
cleavage of cyclopropanes. The coupling of simple
cyclopropanes, CO and alkynes was first reported by
Narasaka,[8] albeit with low catalyst turnover and limited
substrate scope (Scheme 3b). Use of more reactive vinyl
cyclopropanes and cyclopropanes containing a directing group
(DG) were recently developed by Yu[9] and Bower[10] respectively,
both of which exhibit excellent reactivity and selectivity. Hence,
methods that directly activate simple cyclobutanones should
offer a complementary approach to the prior (3+2+1) reactions
without the need for CO gas or auxiliary DGs.
One main difficulty associated with the fused-ring formation
arises from the need for C−C cleavage/coupling at the more
sterically hindered C2 (proximal) position (Scheme 2a), as the
selectivity typically favors the less bulky C4 (distal) position
[a]
L. Deng, L. Jin, G. Dong
Department of Chemistry, University of Chicago
Chicago, IL 60637 (USA)
L. Jin
College of Chemical Engineering, Nanjing University of Science &
Technology
Nanjing 210094 (P. R. China)
E-mail:gbdong@uchicago.edu
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/anie.201712487
Angewandte Chemie International Edition
COMMUNICATION
O
and
"Cut
Sew" with
Ph
Ph
simple cyclobutanones
Ph
a)
5 mol%
16 mol% PMe2Ph
Cl
[Rh(CO)2
]
2
R1
R1
O
O
125 o
C
O
Y
X
work
this
R2
1,4-dioxane,
Y
X
2a'
(4+2)
"standard conditions"
R2
1a
2a
obtained)
R3
(X-ray
2a[b]
R3
2a'[b]
Entry
[b]
conversion
Variations from standard conditions
work on
Prior
with
cyclopropanes
b)
(3+2+1) cycloaddition
none
82%
>95%
<5%
13%
0%
1
2
3
4
5
6
7
8
Narasaka
(1999)
without
without
Cl]2
0%
[Rh(CO)2
R1
R1
R1
PMe Ph
2
0%
0%
>95%
50%
78%
20 mol%
[Rh]
CO2Et
CO2Et
CO2Et
CO2Et
O
CO2Et
CO2Et
PPh3 instead of PMe2Ph
PMePh2 instead of PMe2Ph
PMe3 instead of PMe2Ph
10 mol% PMe2Ph
35%
50%
57%
64%
<5%
12%
8%
Rh
CO
>95%
>95%
8%
10%
24%
<5%
41%
R2
Yu
(2010)
R2
R2
20 mol% PMe2Ph
O
NTs
H4 2Cl]2 instead of
Cl]2
[Rh(CO)2
9
trace
trace
trace
[Rh(C2
)
<5%
10 mol%
CO
[Rh]
NTs
NTs
10
11
12
instead of
Cl]2
[Rh(CO)2
trace
11%
14%
18%
Rh
<5%
[Rh(cod)Cl]2
in THF
O
57%
77%
90%
60% to 92%
in toluene
at 115 o
>95%
>95%
yield
R3
Bower
(2013)
67%
0%
13
14
C
R3
O
R3
with 100 mol% of 2-amino-3-picoline
0%
<5%
R4
R4
7 mol%
CO
[Rh]
R4
N
O
N
O
N
Rh
NMe2
O
NMe2
[a] run on a 0.1 mmol scale at 125 °C for 60 h. [b] isolated yield.
NMe2
yield
O
30% to 74%
With the optimized conditions in hand, the substrate scope
was next investigated (Table 2). First, different aryl-substituted
alkynes all underwent the “cut and sew” sequence to give the
corresponding tricycle products (2a-2e). Alkyl-substituted
alkynes are also competent coupling partners; primary,
secondary and tertiary alkyl substituents are all tolerated.
Unsurprisingly, increasing the bulkiness on the substituent from
propyl (2g) to isopropyl (2h) to t-butyl (2i) groups reduced the
yield. It is noteworthy that the reaction conditions are both pH
and redox neutral. The acid-labile TBS ether is compatible and
89% yield of product 2j was isolated. In addition, cycloalkyl-
substituted alkynes can be effectively coupled; the generated
vinyl cyclopropane moiety (2m) remained intact. Moreover,
substitution on the arene (2n) or the methylene bridge (2o)
(between the arene and cyclobutanone) is tolerated. The
reduced yield for product 2o is due to the increasing
cyclopropane formation; it is likely that the substitution hindered
the migratory insertion to certain extent. Interestingly, the aniline
linkage provided an indoline scaffold (2p). On the other hand,
the nitrogen linker was also found efficient.[11] With such a linker,
coupling with aryl, alkyl and even silyl-substituted alkynes has
been achieved, and the corresponding 6H-isoindole products
can potentially serve as valuable synthetic building blocks.[10]
Finally, both α and β substituted cyclobutanones can be
employed albeit in moderate yields (eqs 1 and 2), probably
caused by the increased steric hindrance in the substrates.
Scheme 3. Cyclohexenone-fused ring formation via C−C Activation of
cyclopropanes and cyclobutanones.
To
explore
the
proposed
“cut-and-sew”
reaction,
cyclobutanone 1a was employed as the initial substrate (Table
1). After careful optimization, the desired benzo-fused 6-5-6
tricycle product (2a) was ultimately obtained in 82% yield using
[Rh(CO)2Cl]2 and PMe2Ph as the metal-ligand combination
(entry 1). First, control experiments showed that both the
phosphine and Rh played pivotal roles in this reaction (entries 2
and 3). A range of monodentate phosphine ligands was found
effective, and generally, higher conversion was obtained with
more electron-rich ligands (entries 4-6). Surprisingly, one
important factor was the ligand/metal ratio, with 1.6:1 being
optimal (for detailed optimization, see SI). When less ligand was
employed (P/Rh=1:1), the reaction still gave
a complete
conversion albeit with more cyclopropane side product (2a’);
however, increasing the P/Rh ratio to 2:1 completely shut down
the reactivity (entries 7 and 8), which could be attributed to the
generation of inactive trans-Rh(CO)(L)2Cl species. We reason
that the active catalytic species likely contains only one
phosphine ligand, but it is relatively unstable in the absence of
extra PMe2Ph. In addition, use of the more π-acidic [Rh(CO)2Cl]2
as a precatalyst is also crucial to generate the active species; in
contrast, use of more electron-rich Rh-olefin complexes gave
almost no conversions of cyclobutanone 1a (entries 9 and 10). A
survey of solvent effect revealed 1,4-dioxane to be optimal
(entries 11 and 12). At a lower temperature (115 oC), the
reaction can still proceed to give 67% yield (entry 13). Finally,
the temporary DG strategy was not effective likely due to the
difficulty of cleaving the bulkier proximal C−C bond (entry 14).[2c]
Ph
O
Ph
O
Cl]
mol%)
mol%)
[Rh(CO)2 2 (5
e
PM Ph
(16
2
(1)
140 o
C
1,4-dioxane
(0.1 M),
BnO
BnO
40%
yield
>20:1 d.r.
±
±
1u(
2u(
)
)
>20:1 d.r.
Ph
O
O
Ph
as
conditions
above
Me
Me
Table 1. Selected optimization studiesa
(2)
46%
brsm)
(72%
yield
2.5:1 d.r.
±
2v(
)
1v
1.5:1 d.r.
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10.1002/anie.201712487
Angewandte Chemie International Edition
COMMUNICATION
Table 2. Substrate Scope[a]
Me
HO
Me
Me
H
R= Me
O
O
R= Me
H
Li, NH
Li, NH
3 (l)
3 (l)
air
t-BuOH, MeI
59%
12:1 d.r.
H
H
93%
R1
4
3
R1
O
>20:1 d.r.
obtained)
(X-ray
Ph
Cl]
mol%)
O
Y
X
[Rh(CO)2 2 (5
e
PM Ph
2
mol%)
Y
X
R2
2a-t
(16
H
R= Ph
R
HO
H
R= Ph
Ph
O
125 o
C
O
1,4-dioxane
H
(0.1 M),
R2
LDA, EtI
60%
H2 Pd/C
,
Et
64%
6
1a-t
H
>20:1 d.r.
or
2a 2f
H
>20:1 d.r.
6
5
O
obtained)
(X-ray
Me
F
OMe
65%
Cl
Ar
65 o
66%
C
I2
R= Ph
R= Ph
HO
DMSO
Ph
Ph
O
1 atm O2
NaOH
H2O2
cat.
Pd(TFA)2
NMe2Py
R= Ph
Ph
HO
2a
2b
2c
2d
2e
82%
O
82%
76%
O
78%
,
,
,
,
,
cat.
54%
HO
52%
7
O
9
O
Me
Me
O
8
n-Pr
80%
Me
Scheme 4. Synthetic applications
2f 77%
,
2g
2h
2i
49%
,
70%
,
,
With regard to the plausible reaction mechanism, there are
two major questions. One is whether this (4+2) cycloaddition
shares the same catalytic pathway as the (3+2+1) reaction
involving cyclopropane ring opening.[10] The other one is whether
the reaction pathway involves the cleavage of the less hindered
distal C−C bond. To address the first question, control
experiments with cyclopropane side product 2a’ were conducted
(Scheme 5a). Subjecting 2a’ to the standard (4+2) reaction
conditions in the presence of CO gas or to the optimal conditions
developed by Narasaka[8] or Bower[10] for the (3+2+1) reaction
gave no desired 2a product. This result suggests that
cyclopropane formation during the (4+2) reaction is probably
irreversible and 2a’ should not be an intermediate towards
product formation. This observation is also consistent with the
fact that coupling of unactivated cyclopropanes in the absence
of DGs is rather difficult.[8]
OTBS
O
O
O
O
2j
2k
2l
2m
,
89%
61%
74%
58%
Ph
,
,
,
O
O
O
Ph
Ph
OMe
OMe
N
n-Bu
2o
Ts
2n
2p
75%
42%
,
,
33%
6.3:1 d.r.
,
(
)
O
O
O
O
Ph
Ph
Et
TMS
Me
NTs
73%
NTs
NTs
71%
NTs
37%
2q
,
2r
2s
2t
70%
,
,
,
control
a)
experiments
1.3:1 d.r.
(
)
Ph
O
Ph
[a] isolated yields; [b] at 130 oC
results
conditions
conditions
A
B
C
only
2a'
decomposition
?
The intriguing cyclohexanone-fused ring structures generated
from this “cut-and-sew” reaction can be conveniently derivatized
(Scheme 4). Excellent diastereoselectivity was obtained in most
cases possibly driven by forming less strained 5-6 cis-fused
rings. First, dissolving metal reduction, followed by alkylation or
oxidation, afforded the α-disubstituted cyclohexanone products 3
(X-ray structure obtained) and 4 (stereochemistry tentatively
assigned), respectively.[12,13] Moreover, enolate-based alkylation
occurred site- and diastereoselectively at the C6-position of the
cyclohexenone moiety. Pd/C-catalyzed hydrogenation took
place at the syn side to the methine hydrogen and directly gave
the corresponding saturated alcohol. Treatment of product 2a
with base and hydrogen peroxide unexpectedly led to a γ-
hydroxylation product (7).[14] Finally, iodine/DMSO oxidation[15]
converted the tricycle into a functionalized fluorene, and a Pd-
catalyzed aerobic oxidation[16] surprisingly gave 9-fluorenone 9
as the dominant product.
only
2a'
2a
2a'
:
:
:
condition A
condition B
condition C
with 1 atm
"standard conditions"
CO
160 o 48
Cl
,
1 atm
CO
8)
(ref
1,2-dichlorobenzene,
C6 3, PhCN,
C,
h,
130 o
[Rh(CO)2
]
2
,
H3
Na
2SO4,
72 1 atm
h,
CO
10)
(ref
C,
[Rh(cod)Cl]2 P(3,5-CF3
)
13C labelling
b)
experiments
13C
(21%)
Ph
O
conversion
at 100%
82%
Ph
13CO
2a
2Cl]
mol%)
2 (5
O
[Rh(
)
e
PM Ph
mol%)
(16
2
13C
125 o
C
(34%)
Ph
1,4-dioxane,
Ph
O
1a
O
conversion
at 52%
<5% 13
C
49%
2a
1a
CO exchange
c)
Ph
R:
13CO
O
13C
O
CO
13C
CO
Rh
O
[Rh]
[Rh]
R
R
R
Scheme 5. Preliminary Mechanistic Studies
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10.1002/anie.201712487
Angewandte Chemie International Edition
COMMUNICATION
To explore the second question, 13C labeling study was
conducted (Scheme 5b). We hypothesized that, if the reaction
involved cleavage of the less hindered distal C−C bond, a CO
de-insertion and re-insertion into the less hindered alkyl group
would have to occur (vide supra, Scheme 2a). Thus, if this were
the case, use of the Rh catalyst containing 13CO ligands would
introduce 13C-labeled carbonyl moiety into the product. Indeed,
replacement of [Rh(CO)2Cl]2 with [Rh(13CO)2Cl]2 under the
standard reaction conditions afforded product 2a in 82% yield
2012, 2683; l) F. Chen, T. Wang, N. Jiao, Chem. Rev. 2014, 114, 8613;
m) A. Dermenci, J. W. Coe, G. Dong, Org. Chem. Front. 2014, 1, 567;
n) G. Dong, in Top. Curr. Chem., Vol. 346, Springer-Verlag, Berlin,
2014; o) M. Murakami, N. Ishida, in Cleavage of Carbon-Carbon Single
Bonds by Transition Metals, Wiley-VCH Verlag GmbH & Co. KGaA,
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Chen, G. Dong, Chem. Eur. J. 2016, 22, 18290; r) P.-h. Chen, B. A.
Billett, T. Tsukamoto, G. Dong, ACS Cat. 2017, 7, 1340; s) G.
Fumagalli, S. Stanton, J. F. Bower, Chem. Rev. 2017, 117, 9404.
For representative examples, see: a) M. Murakami, T. Itahashi, Y. Ito, J.
Am. Chem. Soc. 2002, 124, 13976; b) L. Souillart, E. Parker, N. Cramer,
Angew. Chem. Int. Ed. 2014, 53, 3001; c) H. M. Ko, G. Dong, Nat.
Chem. 2014, 6, 739; d) L. Souillart, N. Cramer, Angew. Chem. Int. Ed.
2014, 53, 9640; e) E. Parker, N. Cramer, Organometallics 2014, 33,
780; f) L. Souillart, N. Cramer, Chem. Eur. J. 2015, 21, 1863; g) X.
Zhou, G. Dong, J. Am. Chem. Soc. 2015, 137, 13715; h) X. Zhou, H. M.
Ko, G. Dong, Angew. Chem. Int. Ed. 2016, 55, 13867.
[2]
with 21% 13C incorporation. Give that only
5
mol%
[Rh(13CO)2Cl]2 was used, 86% 13CO from the Rh complex has
been transferred into product. When the reaction was terminated
at an earlier stage, higher 13C incorporation (34%) was observed
without significant 13C incorporation in recovered starting
material (for more details, see Supporting Information). These
observations suggested that (i) decarbonylation/CO-reinsertion
must have occurred (Scheme 5c), (ii) the exchange between the
coordinated CO on Rh and the free CO is faster than the
subsequent steps and (iii) reductive elimination of the
rhodacyclopentanone intermediate to give back cyclobutanone
1a is significantly slower than migratory insertion into the alkyne
moiety. Hence, this observation is consistent with the hypothesis
that the reaction may involve cleavage of the less hindered distal
[3]
[4]
For the (6+2) coupling of 2-vinyl cyclobutanones with olefins, see: a) P.
A. Wender, A. G. Correa, Y. Sato, R. Sun, J. Am. Chem. Soc. 2000,
122, 7815; b) T. Matsuda, A. Fujimoto, M. Ishibashi, M. Murakami,
Chem. Lett. 2004, 33, 876; c) T. Matsuda, M. Makino, M. Murakami,
Angew. Chem. Int. Ed. 2005, 44, 4608.
a) D. M. Roundhill, D. N. Lawson, G. Wilkinson, J. Chem. Soc. (A) 1968,
845; b) F. J. McQuillin, K. G. Powell, J. Chem. Soc., Dalton Trans. 1972,
2123; c) M. Murakami, H. Amii, Y. Ito, Nature 1994, 370, 540; d) M.
Murakami, H. Amii, K. Shigeto, Y. Ito, J. Am. Chem. Soc. 1996, 118,
8285; e) G.-W. Wang, N. G. McCreanor, M. H. Shaw, W. G.
Whittingham, J. F. Bower, J. Am. Chem. Soc. 2016, 138, 13501.
a) T. Xu, G. Dong, Angew. Chem. Int. Ed. 2012, 51, 7567; b) T. Xu, H.
M. Ko, N. A. Savage, G. Dong, J. Am. Chem. Soc. 2012, 134, 20005; c)
P.-h. Chen, T. Xu, G. Dong, Angew. Chem. Int. Ed. 2014, 53, 1674; d)
T. Xu, G. Dong, Angew. Chem. Int. Ed. 2014, 53, 10733; e) L. Deng, T.
Xu, H. Li, G. Dong, J. Am. Chem. Soc. 2016, 138, 369; f) G. Lu, C.
Fang, T. Xu, G. Dong, P. Liu, J. Am. Chem. Soc. 2015, 137, 8274.
For representative examples of Ni-catalyzed intermolecular
cyclobutanone/alkyne couplings, see: a) M. Murakami, S. Ashida, T.
Matsuda, J. Am. Chem. Soc. 2005, 127, 6932; b) M. Murakami, S.
Ashida, T. Matsuda, Tetrahedron 2006, 62, 7540; c) P. Kumar, J. Louie,
Org. Lett. 2012, 14, 2026; d) N. Ishida, T. Yuhki, M. Murakami, Org.
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3486; f) Y. Li, Z. Lin, Organometallics 2013, 32, 3003; g) A. Thakur, J. L.
Evangelista, P. Kumar, J. Louie, J. Org. Chem. 2015, 80, 9951; h) M.
Barday, K. Y. T. Ho, C. T. Halsall, C. Aïssa, Org. Lett. 2016, 18, 1756.
For representative examples of (3+2+1) reactions involving
cyclopropanes, see: a) S. Mazumder, D. Shang, D. E. Negru, M.-H.
Baik, P. A. Evans, J. Am. Chem. Soc. 2012, 134, 20569; b) S. Kim, Y.
K. Chung, Org. Lett. 2014, 16, 4352; c) Y. Feng, Z.-X. Yu, J. Org. Chem.
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Bower, J. Am. Chem. Soc. 2015, 137, 8054; e) M. H. Shaw, N. G.
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g) M. H. Shaw, W. G. Whittingham, J. F. Bower, Tetrahedron 2016, 72,
2731.
C−C bond, followed by
a decarbonylation/CO reinsertion
process, though the pathway initiated from direct activation of
the bulkier proximal C−C bond cannot be completely ruled out at
this stage.
[5]
[6]
In summary, we have developed the first intramolecular
coupling between cyclobutanones and alkynes to construct
versatile fused cyclohexenone scaffolds. In this reaction, 2π-
insertion can selectively take place at the more sterically
hindered proximal position, which significantly extends the “cut-
and-sew” scope with cyclobutanones thereby opening the door
for accessing other fused structures. Detailed mechanistic
studies are ongoing in our laboratory.
Acknowledgements
[7]
We acknowledge NIGMS (R01GM109054-01) for funding. L.J. is
supported by a CSC fellowship. We thank Mr. Ki-young Yoon for
X-ray structures, Dr. Antoni Jurkiewicz for NMR advices and Dr.
Jin Qin for MS advices. We thank Mr. Renhe Li for checking the
experiment, and Mr. Jianchun Wang for discussions about the
reaction mechanism.
Keywords: rhodium catalysis • cyclobutanone • fused ring
synthesis • C‒C activation• cut-and-sew
[8]
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[11] Extending the linker to form 6-6 fused rings has also been attempted.
While the desired product can be obtained, the yield was rather low (8-
10%) and decarbonylation to form the cyclopropane side product was
dominant, which can be explained by a slow migratory insertion step.
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[13] CCDC 1589374-1589376 contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre
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10.1002/anie.201712487
Angewandte Chemie International Edition
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[14] A. Garcia-Cabeza, R. Marin-Barrios, R. Azarken, F. J. Moreno-Dorado,
M. J. Ortega, H. Vidal, J. M. Gatica, G. M. Massanet, F. M. Guerra, Eur.
J. Org. Chem. 2013, 8307 and references therein.
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Catal. 2016, 358, 4093.
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This article is protected by copyright. All rights reserved.

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COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Lin Deng, Likun Jin, and Guangbin
Dong*
R1
O
R1
simple cyclobutanones
versatile
R1
O
fused scaffolds
Y
X
Page No. – Page No.
Y
X
R2
O
Rh
Y
X
Rh
cleavage of the bulkier
R2
−
Fused-Ring Formation via an
Intramolecular “Cut-and-Sew”
Reaction between Cyclobutanones
and Alkynes
R3
33-89%
C C bond
sew
cut
R2
R3
auxiliary directing
group
R3
yield
examples
22
A catalytic intramolecular “cut-and-sew” transformation between cyclobutanones
and alkynes is developed to construct cyclohexenone-fused rings. The reaction
selectively couples at the more sterically hindered proximal position without the
need for auxiliary directing groups.
This article is protected by copyright. All rights reserved.