Formation of carbocycles via a 1,4-Rh shift triggered by a rhodium-catalyzed addition of terminal alkynes to 3,3-diarylcyclopropenes

Article abstract of DOI:10.1021/acs.orglett.5b00984

The catalytic addition of terminal alkynes to 3,3-diarylcyclopropenes in the presence of a Rh(I)/binap complex proceeded to give the cycloaddition products in good yields, where a 1,4-Rh shift is involved as a key step.

Full text of DOI:10.1021/acs.orglett.5b00984

Letter
pubs.acs.org/OrgLett
Formation of Carbocycles via a 1,4-Rh Shift Triggered by a Rhodium-
Catalyzed Addition of Terminal Alkynes to 3,3-Diarylcyclopropenes
Takahiro Sawano,† Minoru Hashizume, Shouta Nishimoto, Keiyu Ou, and Takahiro Nishimura*
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
S
* Supporting Information
ABSTRACT: The catalytic addition of terminal alkynes to 3,3-diary-
lcyclopropenes in the presence of a Rh(I)/binap complex proceeded to give
the cycloaddition products in good yields, where a 1,4-Rh shift is involved as
a key step.
ransition-metal-catalyzed addition of terminal alkynes to
carbon−carbon double bonds is a highly atom-economical
Scheme 1. Rh-Catalyzed Addition of Alkyne 2m to 3,3-
Diphenylcyclopropene (1a)
T
and straightforward method to introduce an alkyne unit with
the formation of a carbon−carbon bond.1 Of a variety of
transition-metal catalysts for the alkynylation reaction,2−7 Rh
catalysts have been recently developed to achieve the addition
of terminal alkynes to α,β-unsaturated carbonyl compounds,8
nitroalkenes,9 allenes,10 and strained bicyclic alkenes in high
yields.11
Addition of nucleophiles to cyclopropenes, which have
strained reactive double bonds, has provided an easy access to
multisubstituted cyclopropanes, which are often included in
bioactive molecules.12 There have been several reports on the
transition-metal-catalyzed addition of boron,13 tin,14 silane,14a,d
and carbon nucleophiles to cyclopropenes.15,16 The catalytic
addition reaction of terminal alkynes to cyclopropenes was first
reported by Chisholm and co-workers,3b where a variety of
terminal alkynes are introduced into the cyclopropane rings in
high yields by use of a Pd catalyst. Tenaglia reported that a
highly diastereoselective alkynylation of unsymmetrically
substituted cyclopropenes is achieved using a bulky Her-
mann−Beller phosphapalladacycle catalyst.3d In this context, we
found that the reaction of 3,3-diarylcyclopropenes with
terminal alkynes proceeded in the presence of a Rh catalyst
to give cycloaddition products, which are formed via a C−H
activation of an aromatic ring. Here we report the rhodium-
catalyzed cycloaddition reaction involving a 1,4-Rh shift as a
key step.
addition of in situ generated alkynylrhodium(I)17 to 1,1-
diphenylcyclopropene (1a) forms alkylrhodium A, which
undergoes a 1,4-Rh shift to form arylrhodium B.18 The
intramolecular arylation of the alkyne gives alkenylrhodium
C,19 followed by the protonation giving 3am. Since the
pioneering studies of the 1,4-Rh shift by Miura and co-workers
Treatment of 3,3-diphenylcyclopropene (1a) with terminal
alkyne 2m (1.2 equiv) in the presence of [Rh(OAc)(C2H4)2]2
(5 mol % Rh) and ( )-binap (6 mol %) in tetrahydrofuran
(THF) at 40 °C for 3 h gave cycloaddition product 3am in 80%
yield along with the formation of a small amount of addition
product 4am (6% yield) (Scheme 1). The formation of 3am
can be explained by the following proposed mechanism. The
Received: April 6, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b00984
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
in 2000,18a the reaction involving the 1,4-Rh shift has been
developed as a useful method for the construction of multiple
carbon−carbon bonds successively.18,19a,20,21 Very recently,
Shintani and Nozaki reported a Rh-catalyzed polymerization
of 3,3-diarylcyclopropenes, where a 1,4-rhodium migration of a
cyclopropylrhodium(I) species cis to an aromatic ring takes
place to form an arylrhodium(I) intermediate.18m
Scheme 2. Rh-Catalyzed Addition of Alkyne 2 to 3,3-
Diarylcyclopropenes 1
a
A proper choice of the ligand was found to be essential for
the formation of the cycloaddition products in good yield
(Table 1). In contrast to the reaction with ( )-binap giving an
a
Table 1. Ligand Effects
b
b
entry
ligand
3am (%)
4am (%)
c
1
2
3
4
5
6
( )-binap
dppe
81 (80)
6
7
2
1
3
0
5
4
1
1
3
0
dppp
dppb
dppf
xantphos
( )-binap
d
c
7
88 (85)
a
Reaction conditions: 1a (0.20 mmol), 2m (0.24 mmol), [Rh(OAc)-
(C2H4)2]2 (0.0050 mmol, 0.010 mmol of Rh), ligand (0.012 mmol),
a
Reaction conditions: 1 (0.24 mmol), 2 (0.20 mmol), [Rh(OAc)-
b
1
(C2H4)2]2 (0.01 mmol of Rh), ( )-binap (0.012 mmol), THF (1.0
mL) at 40 °C for 3 h. Isolated yields are shown. For 24 h.
THF (1.0 mL) at 40 °C for 3 h. Determined by H NMR using
b
c
d
nitromethane as an internal standard. Isolated yields. 1a (0.24
mmol), 2m (0.20 mmol).
position gave the corresponding cycloaddition products 3gn
and 3hn in 55% and 51% yield, respectively, where an attack of
the alkyne 2n from the side of the alkyl group result in the
formation of the addition product 4gn and 4hn in 27% and
36% yield, respectively (Scheme 3).
80% yield of the cycloaddition product 3am (entry 1),
bisphosphine ligands, such as dppe, dppp, dppb, dppf, and
xantphos, were ineffective in catalyzing the formation of both
the cycloaddition product 3am and the alkynylation product
4am (entries 2−6).22 The use of a slight excess of cyclopropene
1a improved the yield of 3am (85% yield, entry 7).23
Scheme 3. Rh-Catalyzed Addition of Alkyne 2n to
Unsymmetrically Substituted Cyclopropenes
The results obtained for the addition of terminal alkynes to
3,3-diarylcyclopropens are summarized in Scheme 2. The
reactions with silylacetylenes, such as ((diisopropyl)(4-
methoxyphenyl)silyl)acetylene (2m), (triisopropylsilyl)-
acetylene (2n), (tert-butyldimethylsilyl)acetylene (2o), and
(methyldiphenylsilyl)acetylene (2p), proceeded to give the
corresponding cycloaddition products in 39−90% yields, where
the use of alkynes substituted with a bulkier silyl group gave a
higher yield of the product. A sterically hindered terminal
alkyne 2q other than silylacetylenes is also applicable to give the
cycloaddition product 3aq in 50% yield. On the other hand, in
the reaction with 1-octyne, either the cycloaddition product or
the addition product was not formed due to the alkyne
oligomerization. The reactions of (triisopropylsilyl)acetylene
(2n) with 3,3-diarylcyclopropenes having both the electron-
withdrawing (Cl, F) and -donating groups (OMe, Me) at the
para-position gave the corresponding products 3bn−en in
moderate to good yields (63−93% yields). In the reaction of
cyclopropene 1f possessing m-tolyl groups, the 1,4-Rh shift
selectively took place at the less hindered C−H bond to give
3fn in 65% yield. The observed selectivity of the 1,4-Rh shift is
similar to those reported in the previous studies.18a,j,21b,d,e
The reaction of unsymmetrically substituted cyclopropenes
1g and 1h bearing a cyclohexyl and an isopropyl group at the 3-
The silyl group at the alkene moiety of 3am can be removed
by treatment of 3am with tetrabutylammonium fluoride
(TBAF) in dimethyl sulfoxide (DMSO) at 90 °C for 20 h.
The reaction gave 5 in 73% yield (Scheme 4). The resulting
cyclic compound 5 was further converted into 1,4-disubstituted
naphthalene 6 in 85% yield in the presence of p-toluenesulfonic
acid monohydrate (pTsOH·H2O).
A deuterium-labeling experiment gave information about the
protonation step in the catalytic cycle (Scheme 5). The reaction
B
DOI: 10.1021/acs.orglett.5b00984
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
available free of charge on the ACS Publications website at
DOI: 10.1021/acs.orglett.5b00984.
Scheme 4. Transformations of 3am
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: tnishi@kuchem.kyoto-u.ac.jp.
Present Address
†Department of Chemistry, University of Chicago, 929 East
57th Street, Chicago, IL 60637.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Areas “Molecular Activation Directed
toward Straightforward Synthesis”, MEXT, Japan, and JSPS
KAKENHI Grant No. 15H03810.
Scheme 5. Deuterium-Labeling Experiment
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ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental procedures and spectroscopic and analytical data
for the substrates and products. The Supporting Information is
C
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Organic Letters
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