Cationic rhodium(I)/bisphosphine complex-catalyzed cyclization of 1,6-diynes with carboxylic acids

Article abstract of DOI:10.1039/b913344e

A cationic rhodium(I)/bisphosphine complex catalyzes carboxylative cyclizations of 1,6-diynes, leading to cyclic dienyl carboxylates, in high yields with high chemo-, regio-, and stereoselectivities under mild reaction conditions. The Royal Society of Che

Full text of DOI:10.1039/b913344e

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Volume 7 | Number 23 | 7 December 2009 | Pages 4801–5036
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COMMUNICATION
FULL PAPER
Ken Tanaka et al.
Peter J. Stang, Jay S. Siegel et al.
Cationic rhodium(I)/bisphosphine
Synthesis and X-ray structural analysis
of platinum and ethynyl-platinum
corannulenes: supramolecular tectons
complex-catalyzed cyclization of
1,6-diynes with carboxylic acids

COMMUNICATION
www.rsc.org/obc | Organic & Biomolecular Chemistry
Cationic rhodium(I)/bisphosphine complex-catalyzed cyclization
of 1,6-diynes with carboxylic acids†‡
Ken Tanaka,* Shunsuke Saitoh, Hiromi Hara and Yu Shibata
Received 6th July 2009, Accepted 4th September 2009
First published as an Advance Article on the web 15th September 2009
DOI: 10.1039/b913344e
A cationic rhodium(I)/bisphosphine complex catalyzes car-
boxylative cyclizations of 1,6-diynes, leading to cyclic dienyl
carboxylates, in high yields with high chemo-, regio-, and
stereoselectivities under mild reaction conditions.
formation of similar vinylidene intermediates (eqn (3)).9 Thus,
the ruthenium-catalyzed carboxylative cyclizations of diynes are
limited to internal 1,6-diynes. Furthermore, a large excess of acetic
acid and elevated reaction temperature are required.
Addition reactions of heteroatom-hydrogen bonds to metal-
lacyclopentadienes are potentially attractive methods for the
synthesis of functionalized dienes.1–9 Wakatsuki and Yamazaki
reported that N-H bonds of thioacetanilide and thiourea, and
a S-H bond of thiocresol react with cobaltacyclopentadienes to
furnish nitrogen- and sulfur-substituted dienes.1 Vollhardt and
co-workers reported that N-H bonds of 2- and 4-pyridones,2
and various NH-amides and imides3 react with the cobaltacy-
clopentadiene to furnish nitrogen-substituted dienes. The addition
reactions of O-H bonds to the metallacyclopentadienes have
been accomplished by using a catalytic amount of ruthenium
complexes. Dixneuf and co-workers reported ruthenium-catalyzed
carboxylative dimerizations of arylacetylenes to form dienyl
carboxylates through ruthenacyclopentatriene intermediates.4,5
Trost and Rudd reported ruthenium-catalyzed cyclizations of
internal 1,6- and 1,7-diynes with water and methanol.6 Car-
boxylative cyclizations of 1,6- and 1,7-diynes catalyzed by a
cationic ruthenium(II) complex were reported by Saa´ and co-
workers.7 The reaction of an internal 1,6-diyne in acetic acid
solvent at 90 ◦C furnished the corresponding five-membered
dienyl carboxylates8 in high yield (eqn (1)).7 However, 1,6-diynes
containing a terminal alkyne moiety reacted with acetic acid to
yield decarbonylative cyclization products presumably due to the
formation of vinylidene intermediates (eqn (2)),7 although 1,7-
diynes containing a terminal alkyne moiety could furnish the
desired dienyl carboxylates.7 In the case of terminal 1,6-diynes,
Lee and co-workers reported carboxylative cyclizations leading
to six-membered dienyl carboxylates presumably through the
(1)
(2)
(3)
On the other hand, our research group demonstrated that
cationic rhodium(I)/biaryl bisphosphine complexes are highly
effective catalysts for [2 + 2 + 2] cycloadditions of both terminal
and internal alkynes presumably through rhodacyclopentadiene
intermediates.10,11 In this Communication, we describe chemo-,
regio-, and stereoselective cyclizations of both terminal and
internal 1,6-diynes with only a slight excess of carboxylic
acids under mild reaction conditions catalyzed by a cationic
rhodium(I)/bisphosphine complex.
We first investigated the reaction of unsymmetrical 1,6-diyne
1a, possessing a methyl group and hydrogen at each alkyne
terminus, and benzoic acid (2a, 1.1 equiv) in the presence of
a cationic rhodium(I)/BIPHEP complex (5 mol %). We were
pleased to find that the reaction proceeded at room temperature
to give the desired cyclic dienyl benzoate 3aa in quantitative
yield with high regioselectivity (Table 1, entry 1). Thus, vari-
ous rhodium(I)/bisphosphine (Fig. 1) complexes were screened.
Cationic rhodium(I) complexes with biaryl bisphosphine ligands
showed high catalytic activity (entries 1–4), and BIPHEP was the
ligand of choice for both the product yield and regioselectivity
(entry 1). Sterically demanding biaryl bisphosphine ligands were
not effective (entries 5 and 6). Among non-biaryl bisphosphine
ligands examined (entries 7–9), dppb was the best for the product
yield and regioselectivity (entry 9). Although the catalytic activity
of the dppb complex was low, complete conversion of 1a could
Department of Applied Chemistry, Graduate School of Engineering, Tokyo
University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
E-mail: tanaka-k@cc.tuat.ac.jp; Fax: +81 42 388 7037; Tel: +81 42 388
7037
† Electronic supplementary information (ESI) available: Compound char-
acterization data including 1H and 13C NMR spectra of all new compounds
and reaction products. See DOI: 10.1039/b913344e
‡ Typical Procedure (Table 2, entry 5): Under an Ar atmosphere, BIPHEP
(7.8 mg, 0.015 mmol) and [Rh(cod)2]BF4 (6.1 mg, 0.015 mmol) were
dissolved in (CH2Cl)2 (2.0 mL) and the mixture was stirred at room
temperature for 30 min. H2 was introduced to the resulting solution
in a Schlenk tube. After stirring at room temperature for 1 h, the
resulting mixture was concentrated to dryness. To the residue was added
a solution of 1a (66.7 mg, 0.300 mmol) and 2d (33.7 mg, 0.330 mmol) in
(CH2Cl)2 (2.0 mL) at room temperature. The mixture was stirred at room
temperature for 16 h. The resulting solution was concentrated and purified
by a silica gel chromatography (hexane/EtOAc = 2:1), which furnished 3ad
(97.4 mg, 0.291 mmol, 97% isolated yield) as a pale yellow oil.
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Table 1 Screening of catalysts for rhodium-catalyzed cyclization of 1,6-
diyne 1a with benzoic acid (2a)a
Table 2 Rhodium-catalyzed cyclizations of 1,6-diynes 1a–f with hydroxy
compounds 2a–fa
Convn % yieldb
Temp/◦C (%)b
(3aa/4aa)
Entry
1
2 (R3)
Ligand, Temp/◦C % 3/4 (% yield)b
Entry Catalyst
1
2
1a 2a (Bz)
1a 2a (Bz)
1a 2b (Ac)
1a 2c (CyCO)
dppb, 60
3aa (84)
1
2
3
4
5
6
7
8
9
[Rh(cod)2]BF4/BIPHEP
rt
rt
rt
rt
100
100
91
92
5
>99 (95:5)
99 (95:5)
91 (87:13)
92 (68:32)
5 (>99:1)
0
25 (>99:1)
11 (>99:1)
35 (>99:1)
96 (>99:1)
0
BIPHEP, rt
BIPHEP, rt
BIPHEP, rt
3aa/4aa = 95:5 (90)
[Rh(cod)2]BF4/Segphos
[Rh(cod)2]BF4/BINAP
[Rh(cod)2]BF4/H8-BINAP
[Rh(cod)2]BF4/xyl-H8-BINAP rt
[Rh(cod)2]BF4/DTBM-Segphos rt
[Rh(cod)2]BF4/dppf
[Rh(nbd)2]BF4/dppe
[Rh(cod)2]BF4/dppb
[Rh(cod)2]BF4/dppb
[Rh(cod)Cl]2/2dppb
[Rh(cod)2]BF4/dppb
3c
4
3ab (90)
3ac (84)
5
6
7
8
1a 2d (t-BuCO) BIPHEP, rt
3ad (97)
1a 2e (Ph)
1a 2f (Me)
1b 2d (t-BuCO) BIPHEP, rt
1c 2d (t-BuCO) BIPHEP, rt
1d 2a (Bz)
1e 2a (Bz)
1f 2a (Bz)
BIPHEP, rt
BIPHEP, rt
3ae/4ae (0)
3af/4af (0)
3bd (63)
0
rt
rt
rt
60
rt
rt
26
50
36
100
0
9
3cd/4cd = 85:15 (87)
10
11
12
BIPHEP, rt
H8-BINAP, rt
H8-BINAP, 40
3da (88)
10
11
12c
3ea (73)
3fa (87, E/Z = 95:5d)
0
0
a [Rh(cod)2]BF4 (0.015 mmol), ligand (0.015 mmol), 1a–f (0.30 mmol),
2a–f (0.33 mmol), and (CH2Cl)2 (2.0 mL) were used. The active catalyst
was generated in situ by hydrogenation. b Isolated yield. c 2b: 2 equiv.
d Stereochemistry of the enol double bond.
a Rh complex (0.0050 mmol of Rh), ligand (0.0050 mmol), 1a (0.10 mmol),
2a (0.11 mmol), and (CH2Cl)2 (1.5 mL) were used. The active catalyst was
generated in situ by hydrogenation. b Convn and yield were determined by
1H NMR using 1,4-dimethoxybenzene as an internal standard. c Without
hydrogenation.
acids, which is in sharp contrast to the rhthenium-catalyzed
diyne cyclizations.5,6 Thus, phenol (2e, entry 6) and methanol
(2f, entry 7) failed to react with 1a.13,14 With respect to 1,6-
diynes, not only malonate- (1a) but also tosylamide-linked 1,6-
diyne (1b, entry 8) could participate in this reaction. Although
unsymmetrical 1,6-diyne 1c, possessing a phenyl group and
hydrogen at each alkyne terminus, furnished the desired dienyl
carboxylate with moderate regioselectivity (entry 9), unsym-
metrical 1,6-diyne 1d, possessing methyl and phenyl groups at
each alkyne terminus, furnished the desired dienyl carboxylate
with perfect regioselectivity (entry 10). Both terminal and in-
ternal symmetrical 1,6-diynes 1e and 1f reacted with 2a to give
the corresponding dienyl carboxylates in good yields by using
H8-BINAP as a ligand (entries 11 and 12).
be realized by increasing the reaction temperature to 60 ◦C
without erosion of the regioselectivity (entry 10). The use of the
cationic rhodium(I) complex and the treatment of the catalyst with
hydrogen were essential as demonstrated in entries 11 and 12.
Furthermore, the carboxylative cyclization of unsymmetrical
1,7-diyne 1g with 2d also proceeded at room temperature to give
the corresponding six-membered cyclic dienyl carboxylate 3gd in
high yield with perfect regio- and stereoselectivity (eqn (4)).
Fig. 1 Structures of bisphosphine ligands.
Thus, we explored the scope of hydroxy compounds and
1,6-diynes by using 5 mol % of the cationic rhodium(I)/
bisphosphine complex as shown in Table 2. With respect to
hydroxy compounds, not only benzoic acid (2a, entries 1 and
2) but also various aliphatic carboxylic acids (2b–d, entries 3–5)
reacted with 1a to furnish the corresponding dienyl carboxylates
in high yields with perfect regioselectivity.12 Importantly, the
rhodium-catalyzed diyne cyclizations are specific to carboxylic
(4)
The reactions of electron-deficient 1,6-diynes 1h15 and 1i,16 and
1,6-enynes 5a17 and 5b17 with benzoic acid (2a, 1.1 equiv) were also
examined under the same reaction conditions for entry 2 of Table 2
(5 mol % [Rh(cod)2]BF4/BIPHEP at room temperature for 16 h),
while a rapid homo-[2 + 2 + 2] cycloaddition of 1h proceeded
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Table 3 Rhodium-catalyzed cyclizations of 1,6-diyne 1a [Z
C(CO2Me)2] with bifunctional carboxylic acids 2g–ka
=
In the present rhodium-catalyzed addition reactions of car-
boxylic acids to diynes, homo-cyclotrimerizations of diynes are
effectively suppressed, which might suggest strong coordination
of the carboxylic acid to the cationic rhodacyclopentadiene.
Therefore, we anticipated that the reaction of triyne 6 with
benzoic acid (2a) would furnish carboxylative cyclization product
7. Contrary to our expectation, no reaction was observed at room
temperature and cyclotrimerization product 8 was obtained in
quantitative yield at 80 ◦C (eqn (5)).
Entry
1c
2
3
Yield (%)b
2g
3ag
54
2d
2h
3ah
92
3
4
2i
2j
3ai
3aj
92
65
(5)
A possible mechanism for the selective formation of dienyl
benzoate 3aa is shown in Scheme 1. 1,6-Diyne 1a and benzoic
acid (2a) react with the cationic rhodium(I) complex furnishing
rhodacyclopentadiene intermediate A, bearing a chelating car-
boxylate ligand. Regioselective protonation of the sterically less
demanding carbon forms intermediate B. Carboxylate addition to
B generates intermediate C. Elimination of (E)-dienyl benzoate
(E)-3aa followed by the reaction of 1,6-diyne 1a regenerates the
rhodacyclopentadiene intermediate A.18 As the rapid homo-[2 +
2 + 2] cycloaddition of 1a proceeded at room temperature in
the presence of [Rh(cod)2]BF4/BIPHEP (5 mol %) and methyl
benzoate (1.1 equiv), strong deprotonative chelation of benzoic
acid (2a) in the intermediate A might be important to suppress the
homo-[2 + 2 + 2] cycloaddition of 1a.
5
2k
3ak
79
a Reactions were conducted using [Rh(cod)2]BF4 (0.015 mmol), BIPHEP
(0.015 mmol), 1a (0.30 mmol), 2g–k (0.33 mmol), and (CH2Cl)2 (2.0 mL)
at rt for 16 h. The active catalyst was generated in situ by hydrogenation.
b Isolated yield. c Catalyst: 10 mol %. For 64 h. d For 20 h.
quantitatively and no conversions of 1i, 5a, and 5b were observed
(Fig. 2).
Fig. 2 Unsuitable substrates for the carboxylative cyclization.
Next, chemoselective cyclizations of 1,6-diyne 1a with bifunc-
tional carboxylic acids were examined as shown in Table 3. In
terms of the chemoselectivity between a carboxyl O-H group
and a phenolic O-H or an amidic N-H group, the carboxyl
O-H groups of salicylic acid (2g, entry 1) and N-Boc glycine (2h,
entry 2) selectively reacted with 1a to furnish the corresponding
dienyl carboxylates. In terms of the chemoselectivity between the
carboxyl O-H group and various multiple bonds, the carboxyl O-H
groups of acrylic acid (2i, entry 3), phenylpropiolic acid (2j, entry
4), and cyanoacetic acid (2k, entry 5) selectively reacted with 1a to
furnish the corresponding dienyl carboxylates without formation
of [2 + 2 + 2] cycloaddition products.
Scheme 1 Possible mechanism for the formation of 3aa.
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Consistent with this pathway, the reaction of 1,6-diyne 1a and
AcOD (d-2b) led to 87% incorporation of deuterium in the product
d-3ab (eqn (6)).18
5 Recently, alkoxylative dimerization of arylacetylenes to form dienyl
ethers has also been reported; see: M. Zhang, H.-F. Jiang, H. Neumann,
M. Beller and P. H. Dixneuf, Angew. Chem., Int. Ed., 2009, 48,
1681.
6 B. M. Trost and M. T. Rudd, J. Am. Chem. Soc., 2003, 125,
11516.
7 C. Gonza´lez-Rodr´ıguez, J. A. Varela, L. Castedo and C. Saa´, J. Am.
Chem. Soc., 2007, 129, 12916.
8 Dienyl carboxylates have been used for important Diels–Alder partners.
For selected recent examples, see: (a) K. Tiefenbacher, V. B. Arion and
J. Mulzer, Angew. Chem., Int. Ed., 2007, 46, 2690; (b) M. Gay, A. M.
Montana, V. Moreno, M. Font-Bardia and X. Solans, J. Organomet.
Chem., 2005, 690, 4856; (c) H. Suga, A. Kakehi and M. Mitsuda, Bull.
Chem. Soc. Jpn., 2004, 77, 561; (d) S. Serra, E. Brenna, C. Fuganti
and F. Maggioni, Tetrahedron: Asymmetry, 2003, 14, 3313; (e) A. J.
Giessert, L. Snyder, J. Markham and S. T. Diver, Org. Lett., 2003, 5,
1793.
9 H. Kim, S. D. Goble and C. Lee, J. Am. Chem. Soc., 2007, 129, 1030.
10 For reviews, see: (a) K. Tanaka, Chem.–Asian J., 2009, 4, 508; (b) K.
Tanaka, Synlett, 2007, 1977; (c) K. Tanaka, G. Nishida and T. Suda,
J. Synth. Org. Chem. Jpn., 2007, 65, 862.
11 For our first report of cationic rhodium(I)/biaryl bisphosphine
complex-catalyzed [2 + 2 + 2] cycloadditions of alkynes, see: (a) K.
Tanaka and K. Shirasaka, Org. Lett., 2003, 5, 4697. See also: (b) K.
Tanaka, K. Toyoda, A. Wada, K. Shirasaka and M. Hirano, Chem.–
Eur. J., 2005, 11, 1145.
12 The reactions of 1,6-diyne 1a and formic acid in the presence of
the catinonic rhodium(I)/BIPHEP complex (5 mol %) proceeded at
room temperature to yield the corresponding dienyl carboxylates in ca.
30% NMR yield, while the product could not be isolated due to its
instability. The reaction of 1a and oxalic acid was also examined, but
the corresponding addition products were not obtained at all.
13 Intramolecular addition reactions of phenol to acylrhodacycles were
reported; see: M. Murakami, T. Tsuruta and Y. Ito, Angew. Chem., Int.
Ed., 2000, 39, 2484.
14 Intermolecular addition reactions of phenol, methanol, and water to
acylrhodacycles were also reported; see: K. Tanaka and G. C. Fu,
Angew. Chem., Int. Ed., 2002, 41, 1607.
15 Y. Yamamoto, A. Nagata, H. Nagata, Y. Ando, Y. Arikawa, K. Tatsumi
and K. Itoh, Chem.–Eur. J., 2003, 9, 2469.
16 H. Hara, M. Hirano and K. Tanaka, Tetrahedron, 2009, 64, 5093.
17 K. Tanaka, Y. Otake, H. Sagae, K. Noguchi and M. Hirano, Angew.
Chem., Int. Ed, 2008, 47, 1312.
18 The stereoselectivity might be determined at the step of intermediate C
to the product, and the sterically less demanding (E)-isomers [(E)-3aa
and (E)-d-3ab] are generated preferentially.
(6)
In
conclusion,
we
have
demonstrated
cationic
rhodium(I)/bisphosphine complex-catalyzed chemo-, regio-,
and stereoselective cyclizations of 1,6-diynes with carboxylic
acids, leading to cyclic dienyl carboxylates. Importantly, the
present rhodium-catalyzed diyne cyclization allows the use of
both terminal and internal diynes, proceeds under mild reaction
conditions, and is specific to carboxylic acids.
This work was supported partly by Grants-in-Aid for Scientific
Research (Nos. 20675002 and 21∑906) from MEXT, Japan. We
are grateful to Takasago International Corporation for the gift of
Segphos and H8-BINAP derivatives, and Umicore for generous
supports in supplying rhodium complexes.
Notes and references
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ruthenium-catalyzed synthesis of alkylidenecyclobutenes via head-to-
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S. De´rien, B. Demerseman, C. Bruneau, P. H. Dixneuf, L. Toupet, G.
Dazinger and K. Kirchner, Chem.–Eur. J., 2005, 11, 1312.
4820 | Org. Biomol. Chem., 2009, 7, 4817–4820
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The Royal Society of Chemistry 2009
©