Cobalt-Catalyzed Intramolecular Hydroacylation Involving Cyclopropane Cleavage

Article abstract of DOI:10.1002/chem.202001223

A simple cobalt-diphosphine catalyst has been found to efficiently promote intramolecular cyclization of ortho-cyclopropylvinyl- and cyclopropylidenemethyl-substituted benzaldehydes into benzocyclooctadienone and benzocycloheptadienone derivatives, respectively. This ring-opening hydroacylation likely involves aldehyde C?H oxidative addition, olefin insertion, cyclopropane cleavage by β-carbon elimination, and C?C bond-forming reductive elimination, as was supported by mechanistic experiments and DFT calculations.

Full text of DOI:10.1002/chem.202001223

Accepted Article
Accepted Article
Title: Cobalt-Catalyzed Intramolecular Hydroacylation Involving
Cyclopropane Cleavage
Authors: Junfeng Yang, Yuto Mori, Masahiro Yamanaka, and Naohiko
Yoshikai
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To be cited as: Chem. Eur. J. 10.1002/chem.202001223
Link to VoR: https://doi.org/10.1002/chem.202001223
01/2020

10.1002/chem.202001223
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Cobalt-Catalyzed Intramolecular Hydroacylation Involving
Cyclopropane Cleavage
Junfeng Yang,*[a,b] Yuto Mori,[c] Masahiro Yamanaka,*[c] and Naohiko Yoshikai*[a]
Dedication ((optional))
[a]
Dr. J. Yang, Prof. N. Yoshikai
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences
Nanyang Technological University
Singapore 637371, Singapore
E-mail: nyoshikai@ntu.edu.sg
[b]
[c]
Prof. J. Yang
Department of Chemistry
Fudan University
2005 Songhu Road, Shanghai 2000438, P.R. China
Y. Mori, Prof. M. Yamanaka
Department of Chemistry, Faculty of Science
Rikkyo University
3-41-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate))
Abstract: A simple cobalt–diphosphine catalyst has been found to
efficiently promote intramolecular cyclization of ortho-
cyclopropylidenemethyl-substituted
benzocyclooctadienone and
reactions in Scheme 1a and 1b, the present catalytic system does
not require ethylene atmosphere to suppress undesirable
decarbonylation, while ethylene proved not to be a prerequisite
for analogous rhodium-catalyzed reactions reported later.[9]
Mechanistic studies have shed light on the parallelism and
difference between the present cobalt catalysis and the reported
rhodium catalysis.
cyclopropylvinyl-
benzaldehydes
and
into
benzocycloheptadienone derivatives, respectively. This ring-opening
hydroacylation likely involves aldehyde C–H oxidative addition, olefin
insertion, cyclopropane cleavage by β-carbon elimination, and C–C
bond-forming reductive elimination, as supported by mechanistic
experiments and DFT calculations.
(a) Shair et al. (ref 7)
O
O
[Rh(dppe)]ClO4
(20 mol%)
O
H
[Rh]
via:
DCE, 65 °C
ethylene
Ph
Ph
Ph
Introduction
65%
(b) Aïssa and Fürstner (ref 8)
The transition metal-mediated, strain-driven C–C bond cleavage
of small rings allows generation of organometallic intermediates
that are otherwise difficult to access, and can be utilized for a
variety of catalytic bond formation and skeletal rearrangement
reactions.[1,2] Such small ring cleavage typically takes place
through C–C bond oxidative addition or through β-carbon
elimination. In this regard, rhodium represents one of the most
versatile metals for small ring transformations, as it can operate
in both the mechanisms of C–C bond cleavage, thus enabling a
O
[Rh]
[Rh(coe)2Cl]2 (5 mol%)
P(4-MeOC6H4)3 (20 mol%)
O
O
via:
H
DCE, 120 °C
ethylene
76%
(c) This work
O
O
H
CoI2 (5 mol%)
dppp (5 mol%)
■ Operationally simple,
number
of
cycloaddition,
rearrangement,
and
other
ethylene-free
or
O
or
transformations. By contrast, cobalt, the lighter congener of
rhodium, has been only sporadically utilized in catalytic small ring
transformations.[3-6] Herein, we report that cobalt is capable of
emulating the reactivity of rhodium in intramolecular ring-opening
Zn (50 mol%)
DMF, 80 °C
O
■ Common catalyst for
both transformations
H
■ Parallelism and difference
between Co and Rh
hydroacylation
of
vinylcyclopropane[7]
or
Scheme 1. Rh- and Co-catalyzed intramolecular hydroacylation involving
cyclopropane cleavage.
alkylidenecyclopropane[8] that involves a β-carbon elimination
process (Scheme 1a, b). Thus, an inexpensive cobalt–
diphosphine
cyclopropylvinyl-
benzaldehydes
catalyst
promotes
cyclopropylidenemethyl-substituted
benzocyclooctadienone or
conversion
of
ortho-
or
into
The merger of C–H and C–C cleavages in the rhodium(I)-
catalyzed intramolecular hydroacylation[10] was first achieved by
Shair and co-workers using cyclopropyl-substituted 4-pentenals
as substrates (Scheme 1a),[7] and later by Aïssa and Fürstner
benzocycloheptadienone derivatives, respectively, in good yields
under operationally simple conditions (Scheme 1c). Unlike the
1
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using
cyclopropylidenemethyl-substituted
benzaldehydes
6
CoCl2
CoCl2
CoBr2
CoI2
DPEphos
dppp
DMF
DMSO
DMF
DMF
DMF
0
6
(Scheme 1b).[8,9] These eight- or seven-membered ring
formations are commonly proposed to involve aldehyde C–H
oxidative addition, olefin insertion into Rh–H, and β-carbon
elimination of the thus-formed rhodacycles bearing an adjacent
cyclopropyl ring. Meanwhile, we have demonstrated the
competence of a cobalt–chiral diphosphine complex as a catalyst
for enantioselective intramolecular hydroacylation of 2-
alkenylbenzaldehydes,[11,12] which likely operates in the same way
as typical rhodium(I) catalysts. We have also reported cobalt–
diphosphine-catalyzed cycloaddition and cycloisomerization of
tethered alkyne/vinylcyclopropane via cyclopropane cleavage.[3c]
These backgrounds, together with our continuing interest in low-
valent cobalt catalysis,[13] prompted us to investigate the potential
ability of cobalt to promote cyclopropane cleavage in the course
of hydroacylation.
7
55
40
91
92
8
8
dppp
23
0
9
dppp
10[d]
CoI2
dppp
0
[a] The reaction was performed on a 0.1 mmol scale at a concentration of 0.3
M. [b] dppm bis(diphenylphosphino)methane; dppe 1,2-
bis(diphenylphosphino)ethane; dppp 1,3-bis(diphenylphosphino)propane;
dppb 1,4-bis(diphenylphosphino)butane; dppbz 1,2-
bis(diphenylphosphino)benzene; DPEphos = bis[(2-diphenylphosphino)phenyl]
ether. [c] Determined by 1H NMR using 1,1,2,2,-tetrachloroethane as an internal
standard. [d] CoI2 (5 mol%) and dppp (5 mol%) were used.
=
=
=
=
=
The optimized catalytic system was found to promote the ring-
opening hydroacylation of a series of ortho-2-cyclopropylvinyl aryl
aldehydes (Scheme 2). Thus, the starting materials substituted at
the meta- or para-position of the formyl group smoothly underwent
cyclization to afford the corresponding benzocyclooctadienone
derivatives 2b–2i in good to excellent yields. On the other hand,
substrates bearing a substituent ortho to the formyl group (1j), a
thiophene tether (1k), or an alkyl tether (1l) failed to undergo the
desired cyclization. Notably, substrate 1m bearing an alkyl
substituent on the cyclopropyl ring selectively afforded one of two
possible cyclooctenone products, 2m, through cleavage of the
less substituted C–C bond.
Results and Discussion
The present study commenced with a screening of reaction
conditions
for
the
cyclization
of
2-(2-
cyclopropylvinyl)benzaldehyde (1a; Table 1). In light of the
prominent performance of diphosphine ligands in the previously
developed cobalt-catalyzed hydroacylation reactions,[11] several
diphosphines were screened in combination with CoCl2 as the
cobalt source and Zn dust as the reductant. As a result, several
diphoshine ligands such as dppe, dppp, and dppb were found to
promote substantial conversion of 1a in DMF to afford the ring-
opening hydroacylation product 2a (entries 1–6). In particular,
dppp caused full conversion of 1a to afford 2a in 68% yield, which
was accompanied by its olefin regioisomer 2a' as a minor product.
The use of DMSO as the solvent led to a significant drop in the
yield (entry 7), while THF and toluene completely shut down the
conversion of 1a. Notably, the cobalt precatalyst had a profound
influence on the reaction outcome. While the reaction using CoBr2
also produced a mixture of 2a and 2a' (entry 8), the use of CoI2
resulted in a clean and exclusive formation of 2a in 91% yield
(entry 9). An equally high yield was achieved by reducing the
catalyst loading to 5 mol% (entry 10). Note that no simple
hydroacylation product, i.e., 2-cyclopropylindanone, was
observed in these screening experiments.
O
O
CoI2 (5 mol%)
dppp (5 mol%)
H
R
R
Zn (50 mol%)
DMF, 80 °C, 12 h
1a–1i
2a–2i
O
O
O
O
MeO
F
Me
2a, 87%
2b, 84%
2c, 75%
2d, 82%
O
O
O
O
MeO
MeO
F
Me
Me
2e, 81%
2f, 97%
2g, 89%
2h, 84%
Unsuccessful substrates
OMe O
O
Table 1. Effect of reaction conditions.[a]
O
H
O
H
O
O
O
S
CoX2 (10 mol%)
ligand (10 mol%)
H
H
+
Zn (50 mol%)
solvent, 80 °C, 12 h
2i, 81%
1l
1j
1k
1a
2a
2a'
O
CoI2 (5 mol%)
dppp (5 mol%)
O
Entry
CoXn
Ligand[b]
Solvent
Yield [%][c]
H
Pr
Pr
Zn (50 mol%)
DMF, 80 °C, 12 h
2a
0
2a’
0
1m (E/Z = 2:1)
2m, 62%
1
2
3
4
5
CoCl2
CoCl2
CoCl2
CoCl2
CoCl2
dppm
dppe
dppp
dppb
dppbz
DMF
DMF
DMF
DMF
DMF
56
68
30
23
0
Scheme 2. Cyclization of cyclopropylvinyl-substituted benzaldehydes.
20
0
Having demonstrated the feasibility of the vinylcyclopropane-
opening hydroacylation, our attention was next focused on the
alkylidenecyclopropane-opening hydroacylation (Scheme 3). To
4
2
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(a)
our
pleasure,
the
transformation
(3a)
of
(2-
into
O
O
standard
conditions
cyclopropylidenemethyl)benzaldehyde
benzocycloheptadienone 4a was achieved in 91% yield under the
identical reaction conditions as optimized for the
D
81%
0.77D
0.20D
vinylcyclopropane reaction. Likewise, a series of substituted
benzocycloheptadienones 4b–4g could be obtained in moderate
to good yields.
(E)-[D]-1a
[D]-2a
O
O
D
standard
conditions
CoI2 (5 mol%)
dppp (5 mol%)
O
O
90%
H
0.07D
0.88D
Zn (50 mol%)
DMF, 80 °C, 12 h
R
O
(Z)-[D]-1a
R
[D]-2a
3a–3g
4a–4g
(b)
b
O
H
O
O
O
H
H
[Co] H
O
MeO
[Co]
d
MeO
F
c
B
A
4a, 91%
4b, 82%
4c, 50%
4d, 91%
O
a
O
O
2a
O
O
[Co]
[Co]
H
(E)-1a
(Z)-1a
MeO
MeO
[Co]
H
e
C
Cl
F
D
a'
4e, 76%
4f, 89%
4g, 80%
c'
O
H
d'
Scheme 3. Cyclization of cyclopropylidenemethyl-substituted benzaldehydes.
[Co] H
O
H
[Co]
H
B'
A'
To gain mechanistic insight into the present ring-opening
b'
hydroacylation,
we
first
performed
deuterium-labeling
Productive pathways
experiments on the vinylcyclopropane reaction. The reaction of
(E)-[D]-1a took place with predominant deuterium transfer from
the formyl group to the benzylic position of the
benzocyclooctadienone product, accompanied by a minor but
finite degree of deuteration of the vinylic position (Scheme 4a, top).
A near opposite deuteration pattern was observed for the reaction
of (Z)-[D]-1a (Scheme 4a, bottom). To explain these observations,
we formulated a possible catalytic cycle shown in Scheme 4b. The
most straightforward reaction pathway for (E)-1a would involve
C–H oxidative addition to give an acyl(hydrido)cobalt species A,
olefin insertion into Co–H to give a six-membered cobaltacycle B,
β-carbon elimination to give a ring-expanded cobaltacycle D, and
reductive elimination (path a–b–d–e), as is also the case for (Z)-
1a (path a'–b'–d'–e). These pathways should result in transfer of
the aldehyde hydrogen to the benzylic position of the product.
Meanwhile, E/Z isomerization of the olefin moiety could take place
via a common five-membered cobaltacycle C, which coincides
with exchange of the aldehyde-derived hydrogen and the β-styryl
hydrogen. Given this mechanistic model, the results of the
deuterium-labeling experiments suggest that the majority of the
product is formed via the E-isomer-derived cobaltacycle B, while
the other cobaltacycle B' also contributes in part to the product
formation. It is worthwhile to note that the Rh-catalyzed
cyclooctenone formation (Scheme 1a) was proposed to proceed
exclusively via an E-isomer-derived rhodacycle regardless of the
E/Z stereochemistry of the starting material.[7]
(E)-1a: a–b–d–e (major) and a–c–c'–b'–d'–e (minor)
(Z)-1a: a'–c'–c–b–d–e (major) and a'–b'–d'–e (minor)
Scheme 4. Deuterium-labeling experiments and proposed reaction pathways
for the ring-opening hydroacylation of vinylcyclopropane.
Exploration of possible reaction pathways by DFT calculations,
using [Co(dppp)]+ and 1a as the model catalyst and substrate,[14]
suggested that the catalytic cycle in Scheme 4b is qualitatively
reasonable, while providing more insight into the details of the
critical intermediates and transition states as summarized in
Figure 1 (see the Supporting Information for computational
details). From the complex between [Co(dppp)]+ and (E)-1a ((E)-
CP1), we could locate two distinct transition states of aldehyde
C–H oxidative addition, (E)-TS1 and (E)-TS1’, which feature
orientationally opposite approaches of the cobalt center to the
formyl C–H bond, leading to the acyl(hydrido)cobalt intermediates
(E)-CP2 and (E)-CP2’, respectively. The relative orientation of the
Co–H and C=C bonds of (E)-CP2 is suited for alkene insertion
((E)-TS2) leading to the six-membered cobaltacycle eq-CP3,
which bears the cyclopropyl group in the pseudo-equatorial
position. Meanwhile, (E)-CP2’ is connected to the five-membered
cobaltacycle CP3’ via (E)-TS2’. Likewise, the precursor complex
(Z)-CP1 derived from (Z)-1a also has two oxidative addition
pathways leading to the distinct intermediates (Z)-CP2 and (Z)-
CP2’, which further undergo alkene insertion to give six-
membered and five-membered cobaltacycles ax-CP3 and CP3’,
respectively. All the C–H oxidative addition processes were
endergonic, while for each oxidative addition intermediate, the
forward reaction (i.e., alkene insertion) required a much lower
3
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barrier than the reverse reaction (i.e., C–H reductive elimination).
Among the four C–H oxidative addition TSs, those converging to
the five-membered cobaltacycle CP3’ (26.3–28.8 kcal mol–1) were
lower in energy than the others (30.5–31.2 kcal mol–1), which
suggested the feasibility of the interconversion between (E)-CP1
and (Z)-CP1.
With the pseudo-axial orientation of the cyclopropyl group, the
intermediate ax-CP3 derived from (Z)-1a is ready to undergo β-
carbon elimination via ax-TS3 to generate the ring-expanded
cobaltacycle intermediate (Z)-CP4 with cis configuration of the
newly formed C=C bond. This is followed by C–C bond forming
reductive elimination via (Z)-TS4 to afford the product complex
(Z)-PD. On the other hand, direct β-carbon elimination from eq-
CP3 was found to be energetically more demanding (eq-TS3),
leading to less stable intermediate (E)-CP4 with trans
configuration of the C=C bond. In fact, with the pseudo-equatorial
position of the cyclopropyl ring in eq-CP3, we could not locate a
β-carbon elimination TS leading to a cis C=C bond, presumably
because such a TS requires inward orientation of the to-be olefinic
Because of the ring strain associated with the trans C=C bond,
reductive elimination of (E)-CP4 required a high activation energy
((E)-TS4, ΔE = 46.7 kcal mol–1), and the resulting trans-product
complex (E)-PD was less stable than the starting complex by 15.8
kcal mol–1. For eq-CP3 to be productive, it has to transform to ax-
CP3’ (mirror image of ax-CP3) by ring flipping of the cobalt-
containing six-membered ring, which transposes the cyclopropyl
group from the pseudo-equatorial to the pseudo-axial position.
The energy of this ring-flipping TS (TS5; 27.8 kcal mol–1) was
lower than that of (E)-TS1 (30.5 kcal mol–1) and (Z)-TS1 (31.2 kcal
mol–1), suggesting the feasibility of the conversion of eq-CP3 to
(Z)-PD without reverting back to (E)-CP1 and then to (Z)-CP1.
Overall, the energy diagram suggests that 1) the aldehyde C–H
oxidative addition is the rate-determining step, 2) the oxidative
addition from (E)-CP1 is energetically preferred to that from (Z)-
CP1 albeit with a relatively small difference (and hence the latter
may also contribute to the product formation), 3) the five-
membered cobaltacycle CP3’ is a non-productive but important
intermediate connecting (E)-CP1 and (Z)-CP1.
hydrogens, which should cause extremely high ring strain.
(E)-TS4
O
46.7
Co
R
H
R
O
O
R
O
H
Co
Co
R
H
Co
H
(E)-TS1
R
H
O
Co
H
(Z)-TS1
eq-TS3
O
O
R
Co
Co
R
(Z)-TS1’
31.2
H
30.4
30.5
H
H
(E)-TS1’
28.8
Co
O
O
R
Co
(Z)-TS2
26.3
H
H
(Z)-TS2’
O
Co
25.0
TS5
27.8
H
O
(E)-TS2
Co
23.1
22.7
(Z)-CP2’
O
(Z)-TS4
H
H
21.0
20.6
(E)-TS2’
O
19.3
H
Co
15.9
18.4
Co
18.1
(Z)-CP2
O
Co
16.8
R
15.8
ax-TS3
R
H
H
(E)-CP2’
(E)-CP2
O
(E)-PD
(E)-CP4
8.9
12.2
Co
O
11.2
R
R
H
Co
8.8
8.9
O
O
H
eq-CP3
Co
7.4
Co
O
Co
H
ax-CP3’
CP3’
Co
ax-CP3
H
(Z)-CP4
O
H
H
Co
H
0.0
O
H
Co
–0.2
H
H
R
O
H
Co
O
Co
H
(E)-CP1
(Z)-CP1
Co
O
O
R
H
R
–6.6
(Z)-PD
H
H
O
Co
O
Co
Figure 1. Energy diagram of ring-opening hydroacylation of 1a with [Co(dppp)]+. The symbols Co and R in the structural formula refer to the cationic Co(dppp)
moiety and the cyclopropyl group, respectively.
The cycloheptadienone formation from [D]-3a took place
with a clean transfer of the aldehyde deuterium to the newly
formed vinylic position (Scheme 5a), as expected from the
mechanism of the rhodium-catalyzed variant (cf. Scheme
1b).[8] The cobalt catalyst also operated in the same way as the
rhodium catalyst in the reaction of the substrate 3h bearing a
methyl group at the cyclopropyl carbon distal from the benzene
ring (Scheme 5b). The C–C bond cis to the C–aryl bond was
exclusively cleaved to give 4h as the sole product. By contrast,
the cobalt catalyst was found to work differently from the
rhodium catalyst on the substrate 3i bearing a methyl group at
the cyclopropyl carbon proximal to the benzene ring (Scheme
5c). Thus, the cobalt-catalyzed reaction of 3i resulted in a 7:1
mixture of cycloheptenone isomers 4i and 4h along with a
substantial amount of 2-methyleneindanone derivative 5, while
the rhodium catalyst converted 3i exclusively to 4i.
4
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(a)
O
O
O
O
O
standard
O
conditions
[Co]
H
[Co]
[Co]
[Co]
Me
D
71%
H
H
> 0.99D
H
Me
Me
[D]-3a
[D]-4a
Me
E
F
F'
F''
(b)
O
O
O
O
Me
H
H
[Co]
Me
[Co]
O
Me
[Co]
Me
G
– [Co]
G'
H
Me
Co–dppp (this work):
3h
4h
– [Co]
88%
70%
– [Co]
Rh–P(4-MeOC6H4)3 (ref 8):
4h
4i
O
O
O
O
[Co]
H
[Co]
– [Co]
O
O
[Co]
O
H
H
Me
5
Me
Me
+
+
Me
Me
Me
Me
I
J
K
Me
3i
4i
4h
5
Scheme 6. Proposed reaction pathways of 3i under cobalt catalysis.
Co–dppp (this work):
42% (4i:4h = 7:1)
29%
–
Rh–P(4-MeOC6H4)3 (ref 8): 73%
–
Scheme 5. Deuterium-labeling experiment and effect of cyclopropane
substituent on the ring-opening hydroacylation of alkylidenecyclopropane.
Conclusion
In summary, we have reported cobalt-catalyzed cyclization of
cyclopropylvinyl- and cyclopropylidenemethyl-substituted
benzaldehydes, which demonstrate the competence of a
simple cobalt–diphosphine catalyst as an alternative to
rhodium catalysts to promote ring-opening hydroacylation via
β-carbon elimination. The mechanistic study has supported the
parallelism between the cobalt and rhodium catalysts, but also
highlighted the different behaviour of the cobalt catalyst. In light
of the breadth of synthetic transformations involving rhodium-
mediated small ring cleavage,[16] the present finding would hold
promise for further development of small ring transformations
catalyzed by cost-effective cobalt complexes.
The reaction of 3i under the cobalt catalysis may be
rationalized by key steps and intermediates outlined in Scheme
6. Upon C–H oxidative addition, olefin insertion into Co–H in
an exo-fashion leads to the five-membered cobaltacycle
intermediate F. As discussed for the rhodium catalysis,[8]
rotation of the exo C–C bond allows β-carbon elimination from
the conformer F' to form eight-membered cobaltacycle G, while
ensuring the cis geometry of the newly formed C=C bond.
Reductive elimination of
G
then affords the major
cycloheptenone product 4i. Alternatively, β-carbon elimination
may also take place from another conformer F'', although the
resulting cobaltacycle G' would suffer ring strain due to the
trans geometry of the C=C bond. The intermediate G' is
considered to give rise to the minor cycloheptenone 4h. While
the detailed mechanism of trans-to-cis olefin isomerization
remains unclear, the conversion of G’ to 4h might involve a CO
extrusion/reinsertion process as suggested by Aïssa for a
related Rh-catalyzed reaction of alkylidenecyclobutane.[9c] In
addition to these pathways, olefin insertion would also take
place in an endo-fashion, and reductive elimination of the
Experimental Section
General Procedure for Ring-Opening Hydroacylation: In an argon-
filled glove box, a 4-mL vial equipped with a magnetic stir bar was
charged sequentially with CoI2 (4.7 mg, 0.015 mmol), dppp (6.2 mg,
0.015 mmol), zinc powder (9.8 mg, 0.15 mmol), and 2-(2-
cyclopropylvinyl)benzaldehyde
or
2-
(cyclopropylidenemethyl)benzaldehyde derivative (0.30 mmol),
followed by the addition of DMF (0.9 mL). The vial was closed and
removed from the glove box, and the mixture was stirred at 80 °C for
12 h. Upon cooling to room temperature, the reaction mixture was
diluted with ethyl acetate (3 mL) and filtered through a pad of silica gel
with additional ethyl acetate (10 mL) as an eluent. The organic solution
was concentrated under reduced pressure, and the residue was
purified by flash chromatography on silica gel to afford the desired
product.
resulting six-membered cobaltacycle
H would afford a
spirocyclic indanone I. Subsequently, I would be rearranged to
5 via C–C oxidative addition of the cyclopropane moiety,[15] β-
hydride elimination of the cobaltacyclobutane J, and reductive
elimination of the allyl(hydrido)cobalt species K. We speculate
that steric repulsion caused by the methyl group slows the β-
carbon elimination from F', which, in turn, renders the
pathways to the byproducts 4h and 5 feasible. The different
behaviors of the cobalt and rhodium catalysts on 3i might be
ascribed to the shorter ionic radius of cobalt, which would
increase the steric repulsion in F'.
Acknowledgements
This work was supported by the Ministry of Education
(Singapore)
and
Nanyang
Technological
University
(MOE2016-T2-2-043, RG114/18 to N.Y.), JSPS KAKENHI
(Grant Number JP17KT0011 to M.Y.), and National Natural
Science Foundation of China (21901043 to J.Y.).
5
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10.1002/chem.202001223
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Keywords: cobalt • C–H activation • hydroacylation • C–C
bond cleavage • cyclopropanes
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10.1002/chem.202001223
Chemistry - A European Journal
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Entry for the Table of Contents
O
O
H
Ph2P
PPh2
Co
O
O
H
A simple cobalt–diphosphine catalyst efficiently promotes intramolecular ring-opening hydroacylation of vinylcyclopropane and
alkylidenecyclopropane to afford eight- and seven-membered carbocyclic products. The reaction likely proceeds via C–H oxidative
addition, olefin insertion, β-carbon elimination, and C–C reductive elimination as key steps, as supported by mechanistic experiments
and DFT calculations.
Institute and/or researcher Twitter usernames: ny_1978
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