Cu(I)-Catalyzed Coupling and Cycloisomerization of Diazo Compounds with Terminal Yne-Alkylidenecyclopropanes: Synthesis of Functionalized Cyclopenta[ b]naphthalene Derivatives

Article abstract of DOI:10.1021/acs.orglett.8b01812

A Cu(I)-catalyzed coupling and cycloisomerization of diazo compounds with terminal yne-alkylidenecyclopropanes (ACPs) has been presented. This reaction starts from the formation of an allenic intermediate in the Cu(I)-catalyzed cross-coupling reaction of a diazo compound with terminal alkyne in yne-tethered ACP and then undergoes a domino cycloisomerization of a 6π-electrocyclization and cyclopropane ring-opening rearrangement to give functionalized cyclopenta[b]naphthalene derivatives in moderate to excellent yields under mild conditions.

Full text of DOI:10.1021/acs.orglett.8b01812

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Cu(I)-Catalyzed Coupling and Cycloisomerization of Diazo
Compounds with Terminal Yne-Alkylidenecyclopropanes: Synthesis
of Functionalized Cyclopenta[b]naphthalene Derivatives
Peng-Hua Li,† Liu-Zhu Yu,† Xiao-Yu Zhang,† and Min Shi*,†,‡,§
†Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry & Molecular Engineering, East China
University of Science and Technology, 130 Mei Long Road, Shanghai 200237, People’s Republic of China
‡State Key Laboratory and Institute of Elemento-organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
§State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, People’s Republic of China
S
* Supporting Information
ABSTRACT: A Cu(I)-catalyzed coupling and cycloisomerization of
diazo compounds with terminal yne-alkylidenecyclopropanes (ACPs)
has been presented. This reaction starts from the formation of an allenic
intermediate in the Cu(I)-catalyzed cross-coupling reaction of a diazo
compound with terminal alkyne in yne-tethered ACP and then
undergoes a domino cycloisomerization of a 6π-electrocyclization and
cyclopropane ring-opening rearrangement to give functionalized cyclopenta[b]naphthalene derivatives in moderate to excellent
yields under mild conditions.
eq 1).2−6 Along with developments in this field, in recent years,
a new type of metal carbene transformation that involves a
etal carbenes represent useful and versatile intermedi-
1
Mates in modern organic synthesis. Particularly, diazo
cross-coupling process, characterized by a carbene migratory
insertion with diazo compounds, has emerged in the chemical
transformations of metal carbenes. Based on these studies, a
series of novel Cu(I)-catalyzed cross-coupling reactions of N-
tosylhydrazones or other diazo derivatives with terminal
alkynes have been developed by Wang’s group and others,7
affording various substituted allenes or enantiomerically
enriched allenes with broad substrate scope and moderate to
high yields under mild conditions (Scheme 1, eq 2).
Alkylidenecyclopropanes (ACPs), a class of highly strained
but readily accessible compounds, are useful building blocks in
organic synthesis, and numerous cyclizations have been
explored to rapidly generate complex polycyclic frameworks
via a simple manipulation.8 Therefore, based on the previous
works of Cu(I)-catalyzed cross-coupling reactions of N-
tosylhydrazones/diazoalkanes with terminal alkynes and our
previous work on metal-catalyzed cyclizations of ACPs,9 we
envisaged that the reaction of terminal yne-AlkylideneCyclo-
Propanes (ACPs) with diazo compounds in the presence of
Cu(I) catalyst might generate an allene species through a
Cu(I)-carbene migratory insertion, and subsequently, the
allenes might undergo a cycloisomerization with ACPs to
give the multiple ring-fused products (Scheme 1, eq 3). These
polycyclic products might be useful in the synthesis of
biologically active compounds and in material science since
compounds have emerged as useful synthetic intermediates,
which have been widely utilized as carbene precursors, in
synthetic organic chemistry over many decades.2 Thus far, a
great amount of unique transformations based on the reactions
of metal carbenes derived from diazo compounds have been
developed.
Classically, the metal carbene intermediates generated from
diazo compounds in the presence of transition metal catalysts
(Rh, Cu, Pd, Au, etc.) can subsequently undergo a series of X−
H (X = C, O, S, N, etc.) insertion transformations (Scheme 1,
Scheme 1. Transition-Metal-Catalyzed Insertion Reactions
of Diazo Compounds via Metal Carbenes and This Work
Received: June 11, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b01812
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Organic Letters
Letter
they have a similar skeleton with several nature products and
3−6). Since Cu(MeCN)4PF6 has higher Lewis acidity, it
caused the decomposition of the starting materials and the
occurrence of a side reaction. Encouraged by this finding, the
investigation was continued by using Cu(MeCN)4BF4 as the
catalyst. The direct addition of diazo compound 2a without the
use of a syringe pump gave the desired product 3aa in only
30% yield (Table 1, entry 7). Increasing the amount of diazo
compound to 3.0 or 4.0 equiv, the reaction proceeded
smoothly, giving the desired product 3aa in 71% and 81%
yields, respectively, under otherwise identical conditions
(Table 1, entries 8 and 9). Subsequently, various bases were
investigated, and we found that using iPr2NH as base afforded
3aa in 78% yield under the standard conditions (Table 1, entry
10). The use of other organic bases such as iPr2NEt and
DMAP as well as inorganic bases such as K2CO3, Cs2CO3, and
t-BuOK did not improve the reaction outcomes (Table 1,
entries 11−15). Finally, we also evaluated the effect of solvents.
It was found that carrying out the reactions in THF, CH2Cl2,
and DCE afforded 3aa in good yields ranging from 65% to 77%
(Table 1, entries 16−18); however, when MeCN and 1,4-
dioxane were used as the solvents, 3aa was given in lower
yields (Table 1, entries 19 and 20). In addition, the reaction
did not proceed very well in the absence of base or using
catalytic amount of base (Table 1, entries 21 and 22).
Having determined the optimal reaction conditions for this
Cu-catalyzed coupling and cycloisomerization reaction, we
next turned our attention to the scope and limitations with
respect to yne-ACP derivatives 1 in the reaction with methyl
phenyldiazoacetate 2a, and the results are summarized in
Scheme 2. When 4′-chloro-substituted 1b was used as
substrate, the corresponding product 3ba was obtained in
72% yield, and its structure was further confirmed by X-ray
diffraction. For substrates 1c and 1d with two halogen atoms as
substituents in both phenyl rings, the reactions also proceeded
efficiently, giving the corresponding products 3ca and 3da in
fluorophores (Figure 1).10
Figure 1. Selected examples of nature products and fluorophores with
similar skeletons.
The investigation commenced with an evaluation of the
reaction between terminal yne-tethered ACP 1a and methyl 2-
diazo-2-phenylacetate 2a by using different Cu/Rh catalysts
(Table 1). First, with CuI and [Cp*RhCl2]2 as a cocatalyst,3f
Table 1. Optimization of Reaction Conditions for the
Coupling Cycloisomerization
a
b
entry
cat.
base
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
iPr2NH
iPr2NEt
DMAP
K2CO3
Cs2CO3
t-BuOK
Et3N
Et3N
Et3N
Et3N
Et3N
solvent
yield (%)
1
2
3
4
5
6
7
8
9
CuI/[Cp*RhCl2]2 (2)
CuI/[Rh(OAc)2]2 (2)
Cu(OAc)2
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
THF
47
<5
<5
<5
59
12
30
71
81
78
35
54
61
64
57
69
77
65
7
Cu(OTf)2
Cu(MeCN)4BF4
Cu(MeCN)4PF6
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
Cu(MeCN)4BF4
c
d
e
e
10
11
12
13
14
15
16
17
18
19
20
21
e
e
a b
,
Scheme 2. Substrate Scope of the Terminal Yne-ACPs
e
e
e
e
e
CH2Cl2
DCE
MeCN
dioxane
CHCl3
CHCl3
e
e
e
24
<5
16
e
-
ef
,
22
Et3N
a
Reactions were run under the following conditions: a solution of 1a
(0.1 mmol), 2a (0.2 mmol), base (0.1 mmol), and catalysts (10 mol
%) in dry solvent (2.0 mL) was stirred at 25 °C under nitrogen
b
c
atmosphere for 20 h. Isolated yields. The diazo compound 2a was
d
e
added directly. 3.0 equiv of 2a was added. 4.0 equiv of 2a was
added. 0.2 equiv of Et3N was used.
f
the reaction of 1a with 2a in CHCl3 afforded the desired
product 3aa in 47% isolated yield using triethylamine (Et3N)
as a base (Table 1, entry 1). Using CuI and [Rh(OAc)2]2 as a
cocatalyst, 3aa was obtained in less than 5% yield (Table 1,
entry 2). Next, we optimized the reaction conditions by
screening various copper catalysts and found that the use of
Cu(MeCN)4BF4 as a single catalyst could produce 3aa in 59%
yield, although Cu(OAc)2, Cu(OTf)2, and Cu(MeCN)4PF6
are not efficient ones in this transformation (Table 1, entries
a
Unless otherwise specified, all reactions were carried out using 1 (0.1
mmol), 2a (0.4 mmol), Cu(MeCN)4BF4 (10 mol %), and Et3N (0.1
b
c
mmol) in CHCl3 (2.0 mL) at 25 °C. Isolated yields. [Cp*RhCl2]2
(2 mol %) was added, and the reaction was performed at 40 °C. N.R.
= No Reaction.
B
DOI: 10.1021/acs.orglett.8b01812
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Organic Letters
Letter
70% and 74% yields, respectively. Then, we synthesized a
series of 4′-substituted substrates to investigate the electronic
effect at the para-position of the benzene ring. For substrates
1e−1j, regardless of whether they had an electron-rich or
electron-poor aromatic ring, the reactions all proceeded
efficiently to afford the corresponding products 3ea−3ja in
good yields ranging from 61% to 83%. To further evaluate the
generality of this method, substrate 1k, in which the aromatic
ring was replaced by a heteroaromatic thiophene, also gave the
desired product 3ka in 77% yield under the standard reaction
conditions. Moreover, the desired product 3la could also be
isolated in 73% yield when the benzene ring was changed by a
hydrogen atom. However, when cycloalkane-containing
terminal yne-ACP 1m was used to react with 2a under the
standard reaction conditions, only a trace of the desired
product 3ma was detected. Furthermore, substrate 1n, in
which an alkylidenecyclobutane moiety was tethered instead of
alkylidenecyclopropane, did not react with 2a to give the
desired product, thus indicating that the strained three-
membered ring is essential in this copper(I)-catalyzed
transformation.
diazo-2-(4-iodophenyl)acetate 2n was also compatible in the
reaction with 1a, affording the desired product 3an in 66%
yield. The scope of the other type of diazo compounds was
next examined. 2-Diazo-1-phenylethanone 2o is tolerated in
this transformation, giving the corresponding product 3ao in
48% yield if using 2 mol % of [Cp*RhCl2]2 as the cocatalyst.
However, when diethyl 2-diazomalonate 2p and
(diazomethylene)dibenzene 2q were used to react with 1a,
we found that no reaction occurred in both cases even in the
presence of rhodium catalyst or at the elevated temperature.
Moreover, when ethyl 2-diazopropanoate 2r was used to
react with 1a, the compound 3ar′ was obtained in 62% yield
rather than the desired product (Scheme 4, eq 1). To further
Scheme 4. Further Investigations
Next, using unsubstituted yne-ACP 1a as the substrate, a
variety of diazo compounds 2 were examined to expand the
scope of the substrates under the optimal reaction conditions
(Scheme 3). First, we utilized a variety of benzene ring
a b
,
Scheme 3. Substrate Scope of Diazo Compounds
demonstrate the synthetic usefulness of this reaction, a scale-up
experiment was realized with 2.0 mmol of substrate 1a in the
reaction with 2a under the standard conditions, affording 3aa
in 74% isolated yield (559.7 mg) (Scheme 4, eq 2). Reduction
of product 3aa with LiAlH4 in THF gave the corresponding
product 4aa in 94% yield (Scheme 4, eq 3). Furthermore, the
asymmetric variant of this reaction was also examined using
various chiral ligands, but all gave the desired product 3aa as
racemates in 68%−92% yields (see Scheme S4 in the
Supporting Information).
According to the previously reported literature7,9 and our
experimental result, a plausible mechanism for this Cu-
catalyzed coupling and cycloisomerization reaction has been
outlined in Scheme 5. In the presence of a base and a
Scheme 5. Plausible Mechanism for the Formation of 3aa
a
Unless otherwise specified, all reactions were carried out using 1a
(0.1 mmol), 2 (0.4 mmol), Cu(MeCN)4BF4 (10 mol %), and Et3N
b
(0.1 mmol) in CHCl3 (2.0 mL) at 25 °C. Isolated yields.
c
[Cp*RhCl2]2 (2 mol %) was added, and the reaction was carried
out at 50 °C.
substituted diazo compounds to react with 1a and found that
the corresponding cyclopenta[b]naphthalene derivatives 3ab−
3ae and 3ag−3aj were produced in moderate to good yields
ranging from 66 to 83%, regardless of the electronic property
of the substituent and the substituted position on the benzene
ring. However, when methyl 2-(4-cyanophenyl)-2-diazoacetate
2f was used as the dizao compound, a trace of the desired
product was detected under the standard reaction conditions.
Changing the methyl group in the ester moiety to ethyl- and
isopropyl acetates, the reactions also proceeded smoothly to
give the corresponding products 3ak in 83% yield and 3al in
77% yield, respectively. However, in the case of diazo
compound 2m containing a benzyl ester moiety, only a trace
of the desired product 3am was detected. Moreover, ethyl 2-
copper(I) salt, the intermediate of copper acetylide I was first
formed from yne-ACP 1a. Next, the reaction of intermediate I
with diazo compound 2a would lead to the formation of Cu-
carbene species II, which underwent a migratory insertion of
the alkynyl group into the carbenic carbon atom to give the
propargyl copper intermediate III. The allenic intermediate IV
was then formed by protonation of intermediate III,
C
DOI: 10.1021/acs.orglett.8b01812
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
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intermediate IV, which had a highly strained ACP moiety and
highly active allenic structure, could easily generate the
intermediate V through a 6π-electrocyclization at room
temperature. This intermediate subsequently underwent a
vinylcyclopropane rearrangement facilitated by generation of
an aromatic ring to produce the corresponding product 3aa.
In summary, we have disclosed a novel protocol of Cu(I)-
catalyzed coupling and cycloisomerization of diazo compounds
with terminal yne-alkylidenecyclopropanes (ACPs), giving the
functionalized cyclopenta[b]naphthalene derivatives in mod-
erate to good yields under mild conditions. A plausible
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derivatization. We expect that this finding will provide a
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[b]naphthalene derivatives. The potential utilization and
extension of this new synthetic methodology are currently
under investigation in our laboratory.
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ASSOCIATED CONTENT
* Supporting Information
■
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Díaz-Requejo, M. M.; Díaz-Rodríguez, A.; Gonzalez-Nun
S
́
Mello, R.; Munoz, B. K.; Ojo, W. S.; Asensio, G.; Etienne, M.; Perez,
̃
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b01812.
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Accession Codes
CCDC 1569645 contains the supplementary crystallographic
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 Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
■
*Fax: (+86)-21-6416-6128. E-mail: mshi@mail.sioc.ac.cn.
ORCID
Min Shi: 0000-0003-0016-5211
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful for the financial support from the National
Basic Research Program of China (973)-2015CB856603, the
Strategic Priority Research Program of the Chinese Academy
of Sciences, Grant No. XDB20000000 and sioczz201808, the
National Natural Science Foundation of China (20472096,
21372241, 21572052, 20672127, 21421091, 21372250,
21121062, 21302203, 20732008, 21772037, and 21772226),
and the Fundamental Research Funds for the Central
Universities 222201717003.
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