A new route to substituted phenols by cationic rhodium(l)/BINAP complex-catalyzed decarboxylative [2 + 2 + 2] cycloaddition

Article abstract of DOI:10.1021/ol900123d

A new route to substituted phenols has been developed by cationic rhodium(l)/BINAP complex-catalyzed decarboxylative [2 + 2 + 2] cycloadditions of 1,6-and 1,7-diynes with commercially available vinylene carbonate.

Full text of DOI:10.1021/ol900123d

ORGANIC
LETTERS
2009
Vol. 11, No. 6
1337-1340
A New Route to Substituted Phenols by
Cationic Rhodium(I)/BINAP
Complex-Catalyzed Decarboxylative
[2 + 2 + 2] Cycloaddition
Hiromi Hara, Masao Hirano, and Ken Tanaka*
Department of Applied Chemistry, Graduate School of Engineering, Tokyo UniVersity
of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
tanaka-k@cc.tuat.ac.jp
Received January 20, 2009
ABSTRACT
A new route to substituted phenols has been developed by cationic rhodium(I)/BINAP complex-catalyzed decarboxylative [2 + 2 + 2]
cycloadditions of 1,6- and 1,7-diynes with commercially available vinylene carbonate.
Transition-metal-catalyzed [2 + 2 + 2] cycloadditions of
tethered diynes with alkynes have been widely employed
for the regioselective synthesis of substituted aromatic
compounds.1 Instead of alkynes, alkenes possessing a leaving
group can be employed as alkyne equivalents. As such,
Takeuchi and co-workers first reported a neutral iridium(I)/
dppe complex-catalyzed [2 + 2 + 2] cycloaddition of a 1,6-
diyne with n-butyl vinyl ether at elevated temperature
(70 °C), which furnishes a tetrasubstituted benzene through
elimination of n-butanol in moderate yield.2-5 Following this
pioneering report, our research group recently reported
cationic rhodium(I)/BINAP complex-catalyzed [2 + 2 + 2]
cycloadditions6-9 of 1,6-diynes with enol ethers.10 The high
Lewis acidity of the cationic rhodium(I)/BINAP complex
facilitates the elimination of an alcohol even at room
temperature, which significantly improved the yields of the
desired tetra- and pentasubstituted benzenes. Furthermore,
the use of the cationic rhodium(I)/BINAP complex as a
catalyst enabled a [2 + 2 + 2] cycloaddition of 1,6-diyne
1a with ketene acetal 2a at room temperature, which
furnished the corresponding bicyclic methoxybenzene 3aa
in quantitative yield (Scheme 1).10,11
Scheme 1
(1) For recent reviews of transition-metal-catalyzed [2 + 2 + 2]
cycloadditions, see: (a) Tanaka, K. Chem. Asian J. 2009, 4, Epub ahead of
print, DOI: 10.1002/asia.200800378. (b) Varela, J. A.; Saa´, C. Synlett 2008,
2571. (c) Shibata, T.; Tsuchikama, K. Org. Biomol. Chem. 2008, 1317. (d)
Heller, B.; Hapke, M. Chem. Soc. ReV. 2007, 36, 1085. (e) Agenet, N.;
Buisine, O.; Slowinski, F.; Gandon, V.; Aubert, C.; Malacria, M. In Organic
Reactions; Overman, L. E., Ed.; John Wiley & Sons: Hoboken, 2007; Vol.
68, p 1. (f) Chopade, P. R.; Louie, J. AdV. Synth. Catal. 2006, 348, 2307.
(g) Gandon, V.; Aubert, C.; Malacria, M. Chem. Commun. 2006, 2209. (h)
Kotha, S.; Brahmachary, E.; Lahiri, K. Eur. J. Org. Chem. 2005, 4741. (i)
Gandon, V.; Aubert, C.; Malacria, M. Curr. Org. Chem. 2005, 9, 1699. (j)
Yamamoto, Y. Curr. Org. Chem. 2005, 9, 503. (k) Varela, J.; Saa´, C. Chem.
ReV. 2003, 103, 3787.
Takeuchi and co-workers also reported that the neutral
iridium(I)/dppe complex catalyzes a [2 + 2 + 2] cycload-
dition of a 1,6-diyne with a cyclic enol ether (2,3-dihydro-
furan) instead of an acyclic enol ether (n-butyl vinyl ether)
(2) Kezuka, S.; Tanaka, S.; Ohe, T.; Nakaya, Y.; Takeuchi, R. J. Org.
Chem. 2006, 71, 543
.
10.1021/ol900123d CCC: $40.75
Published on Web 02/18/2009
2009 American Chemical Society

to furnish an aromatic alcohol in high yield.3,12,13 Thus, a
[2 + 2 + 2] cycloaddition of 1,6-diyne 1a with a 2,3-dihydro-
1,4-dioxin (2b) was examined in the presence of the cationic
rhodium(I)/BINAP complex (5 mol %). Pleasingly, the
reaction proceeded at room temperature to furnish the
expected ethyleneglycol monoaryl ether 3ab in good yield
(Scheme 2).
be used as a stable equivalent of unstable hydroxyacetylene
(Scheme 3).
Scheme 3
Scheme 2
We first investigated the reaction of 1,6-diyne 1a and
vinylene carbonate (2c, 5 equiv) in the presence of the
cationic rhodium(I)/BINAP complex (5 mol %). We were
pleased to find that the expected decarboxylative [2 + 2 +
2] cycloaddition proceeded at room temperature to give the
corresponding bicyclic phenol 3ac in 64% yield (Table 1,
We anticipated that the use of commercially available
vinylene carbonate (2c) instead of 2,3-dihydro-1,4-dioxin
(2b) would furnish substituted bicyclic phenols through
elimination of carbon dioxide.14-16 If this new route to
phenol derivatives is realized, vinylene carbonate (2c) can
(3) For the first discovery of a neutral iridium(I)/bisphosphine complex-
catalyzed [2 + 2 + 2] cycloaddition of alkynes, see: (a) Takeuchi, R.;
Tanaka, S.; Nakaya, Y. Tetrahedron Lett. 2001, 42, 2991. For their related
reports, see: (b) Takeuchi, R.; Nakaya, Y. Org. Lett. 2003, 5, 3659. (c)
Kezuka, S.; Okado, T.; Niou, E.; Takeuchi, R. Org. Lett. 2005, 7, 1711.
(d) Onodera, G.; Matsuzawa, M.; Aizawa, T.; Kitahara, T.; Shimizu, Y.;
Table 1. Screening of Reaction Conditions for [2 + 2 + 2]
Cycloaddition of 1,6-Diyne 1a with Vinylene Carbonate (2c)a
Kezuka, S.; Takeuchi, R. Synlett 2008, 755
(4) For a review of neutral iridium(I)/bisphosphine complex-catalyzed
enantioselective [2 + 2 + 2] cycloadditions, see ref 1c.
.
(5) Although palladium-catalyzed [2 + 2 + 2] cycloadditions of dimethyl
acetylenedicarboxylate with vinyl ethers and esters were reported, the
reactions required a large excess of the vinyl compounds and a long reaction
time; see: Stephan, C.; Munz, C.; Dieck, H. T. J. Organomet. Chem. 1993,
452, 223
.
(6) For the first discovery of a cationic rhodium(I)/biaryl bisphosphine
complex-catalyzed [2 + 2 + 2] cycloaddition of alkynes, see: (a) Tanaka,
K.; Shirasaka, K. Org. Lett. 2003, 5, 4697. See also: (b) Tanaka, K.; Toyoda,
K.; Wada, A.; Shirasaka, K.; Hirano, M. Chem. Eur. J. 2005, 11, 1145
.
(7) For our accounts of cationic rhodium(I)/biaryl bisphosphine complex-
catalyzed [2 + 2 + 2] cycloadditions, see: (a) Tanaka, K. Synlett 2007,
1977. (b) Tanaka, K.; Nishida, G.; Suda, T. J. Synth. Org. Chem. Jpn. 2007,
entry
catalyst
temp (°C) convn (%)b yield (%)b
1
2
3
4
5
6
7
8
9
[Rh(cod)2]BF4/BINAP
[Rh(cod)2]BF4/Segphos
[Rh(cod)2]BF4/H8-BINAP
[Rh(nbd)2]BF4/dppe
[Rh(cod)Cl]2/2BINAP
[Ir(cod)2]BF4/BINAP
[Ir(cod)Cl]2/2BINAP
[Ir(cod)Cl]2/2dppe
rt
rt
rt
rt
rt
rt
rt
rt
40
85
83
100
48
0
0
0
0
100
64
29
54
18
0
0
0
0
76
65, 862
.
(8) For a review of rhodium-catalyzed [2 + 2 + 2] cycloadditions, see:
Fujiwara, M.; Ojima, I. In Modern Rhodium-Catalyzed Organic Reactions;
Evans, P. A., Ed.; Wiley-VCH: Weinheim, 2005; p 129
.
(9) For cationic rhodium(I)/biaryl bisphosphine complex-catalyzed [2
+ 2 + 2] cycloadditions involving monoenes, see: (a) Tsuchikama, K.;
Kuwata, Y.; Shibata, T. J. Am. Chem. Soc. 2006, 128, 13686. (b) Tanaka,
K.; Nishida, G.; Sagae, H.; Hirano, M. Synlett 2007, 1426. (c) Shibata, T.;
Kawachi, A.; Ogawa, M.; Kuwata, Y.; Tsuchikama, K.; Endo, K. Tetra-
hedron 2007, 63, 12853. (d) Shibata, Y.; Noguchi, K.; Hirano, M.; Tanaka,
K. Org. Lett. 2008, 10, 2825. (e) Tanaka, K.; Takahashi, M.; Imase, H.;
[Rh(cod)2]BF4/BINAP
a [Rh(cod)2]BF4 (0.0075 mmol), ligand (0.0075 mmol), 1a (0.150 mmol),
Osaka, T.; Noguchi, K.; Hirano, M. Tetrahedron 2008, 64, 6289
.
2c (0.750 mmol), and CH2Cl2 or (CH2Cl)2 (0.8 mL) were used. b Determined
(10) (a) Hara, H.; Hirano, M.; Tanaka, K. Org. Lett. 2008, 10, 2537.
(b) Hara, H.; Hirano, M.; Tanaka, K. Submitted for publication.
(11) For cationic rhodium(I)/BINAP complex-catalyzed [2 + 2 + 2]
cycloadditions of diynes with alkynyl ethers en route to aryl ethers, see:
1
by H NMR.
Clayden, J.; Moran, W. J. Org. Biomol. Chem. 2007, 5, 1028
.
(12) A cobalt-mediated [2 + 2 + 2] cycloaddition of an alkynylboronic
pinacolate ester with 2,3-dihydrofuran was reported. Not the corresponding
aromatic alcohol but the corresponding diborylated cyclohexadiene was
obtained as a major product; see: Geny, A.; Leboeliguf, D.; Rouquie´, G.;
Vollhardt, K. P. C.; Malacria, M.; Gandon, V.; Aubert, C. Chem. Eur. J.
entry 1). Thus, various rhodium(I)/bisphosphine complexes
were screened. Cationic rhodium(I) complexes with bispho-
sphine ligands (BINAP, Segphos, H8-BINAP, and dppe) were
able to catalyze this reaction (entries 1-4), and BINAP was
the best for the product selectivity (entry 1).17 On the other
hand, a neutral rhodium(I)/BINAP complex and both cationic
and neutral iridium(I)/BINAP complexes were not able to
catalyze this reaction at all (entries 5-7). The neutral
2007, 13, 5408
.
(13) For transition-metal-catalyzed [2 + 2 + 2] cycloadditions of 1,6-
diynes with 2,5-dihydrofuran to form substituted bicyclic cyclohexadienes,
see: (a) Yamamoto, Y.; Kitahara, H.; Ogawa, R.; Itoh, K. J. Org. Chem.
1998, 63, 9610. (b) Varela, J. A.; Rubin, S. G.; Gonza´lez-Rodr´ıguez, C.;
Castedo, L.; Saa´, C. J. Am. Chem. Soc. 2006, 128, 9262
.
1338
Org. Lett., Vol. 11, No. 6, 2009

iridium(I)/dppe complex, which was employed for the [2 +
2 + 2] cycloaddition of a 1,6-diyne with enol ethers,3 showed
no catalytic activity (entry 8). Increasing the reaction
temperature to 40 °C realized complete conversion of 1a,
which improved the yield of 3ac to 76% (entry 9).
Thus, we explored the scope of 1,6-diynes by using 5 equiv
of vinylene carbonate (2c) and 5 mol % of the cationic
rhodium(I)/BINAP complex as shown in Table 2. With
4), tosylamide- (1d, entry 5), and oxygen-linked (1e, entry
6) internal 1,6-diynes could be employed for this reaction.
With respect to substituents at alkyne termini, not only
methyl- (1a-e, entries 1-6) but also ethyl- (1f, entry 7) and
phenyl-substituted (1g, entry 8) internal 1,6-diynes could
participate in this reaction.18 Unfortunately, terminal 1,6-
diyne 1h reacted with 2c to give the corresponding bicyclic
phenol 3hc in low yield even using a large excess of 1h (25
equiv) due to the rapid homo-[2 + 2 + 2] cycloaddition of
1h (entry 9). Although elevated temperature (80 °C) was
necessary, the catalyst loading could be reduced to 2 mol %
with only a slight erosion of the product yield (entry 2).
Next, the reactions of 1,7-diynes and vinylene carbonate
(2c) were investigated as shown in Table 3. The reaction of
Table 2. Cationic Rh(I)/BINAP-Catalyzed Decarboxylative [2 +
2 + 2] Cycloadditions of 1,6-Diynes 1a-h with 2ca
Table 3. Cationic Rh(I)/BINAP-Catalyzed Decarboxylative [2 +
2 + 2] Cycloadditions of 1,7-Diynes 1i-m with 2ca
a Reactions were conducted using [Rh(cod)2]BF4 (0.015 mmol), BINAP
(0.015 mmol), 1i-m (0.300 mmol), 2c (1.50 or 7.50 mmol), and (CH2Cl)2
(2.0 mL) at 40 °C for 16 h. b Isolated yield. c At 80 °C for 40 h.
ethanetetracarboxylate-linked 1,7-diyne 1i and 2c (5 equiv)
proceeded in high yield (entry 1), whereas that of 2,8-
decadiyne 1j and 2c proceeded in low yield even using excess
2c (25 equiv, entry 2). With respect to substituents at the
alkyne termini, the reaction with ethyl-substituted internal
1,7-diyne 1k (entry 3) proceeded in higher yield than that
with methyl-substituted internal 1,7-diyne 1j because of the
slow homo-[2 + 2 + 2] cycloaddition of 1k (entry 3). In
the case of phenyl-substituted 1,7-diyne 1l, the corresponding
bicyclic phenol 3lc was obtained in good yield at elevated
temperature (80 °C, entry 4). Like the reaction with terminal
1,6-diyne 1h, terminal 1,7-diyne 1m was not a suitable
a Reactions were conducted using [Rh(cod)2]BF4 (0.015 mmol), BINAP
(0.015 mmol), 1a-h (0.300 mmol), 2c (1.50 or 7.50 mmol), and (CH2Cl)2
(2.0 mL) at 40 °C for 16 h. b Isolated yield. c Catalyst: 2 mol %. At 80 °C
for 20 h. d Isolated as a mixture of 3bc and dimer of 1b. Yield of 3bc was
1
determined by H NMR.
respect to tethers, not only malonate- (1a, entry 1) but also
acetylacetone- (1b, entry 3), dimethoxypropane- (1c, entry
Org. Lett., Vol. 11, No. 6, 2009
1339

coupling partner for 2c due to the rapid homo-[2 + 2 + 2]
cycloaddition of 1m, and thus the corresponding cycloadduct
3mc was obtained in only a trace amount (entry 5).
A possible mechanism for the present decarboxylative [2
+ 2 + 2] cycloaddition of 1,6- and 1,7-diynes 1 with
vinylene carbonate (2c) is shown in Scheme 4. Diyne 1 reacts
carbonate B would facilitate the elimination of carbon dioxide
to form bicyclic phenol 3.
In conclusion, we have developed a new route to substi-
tuted phenols by cationic rhodium(I)/BINAP complex-
catalyzed decarboxylative [2 + 2 + 2] cycloadditions of 1,6-
and 1,7-diynes with commercially available vinylene carbon-
ate. Application of the present decarboxylative cycloaddition
approach to various annulation reactions and developing
asymmetric variants of this reaction are underway in our
laboratory.
Scheme 4
Acknowledgment. This work was supported partly by a
Grant-in-Aid for Scientific Research (no. 20675002) from
JSPS, Japan. We are grateful to Takasago International
Corporation for the gift of Segphos and H8-BINAP, and
Umicore for generous supports in supply of rhodium and
iridium complexes.
Supporting Information Available: Experimental pro-
cedures and compound characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
with rhodium to form rhodacyclopentadiene intermediate A.
Subsequent insertion of 2c followed by reductive elimination
of rhodium furnishes carbonate B.19 Coordination of the
cationic rhodium(I) complex to the carbonyl group of
OL900123D
(16) A synthesis of substituted 1-naphthols through Diels-Alder reaction
of 3-silylbenzynes with substituted furans followed by acid-mediated
aromatization was reported; see: Akai, S.; Ikawa, T.; Takayanagi, S.-I.;
Morikawa, Y.; Mohri, S.; Tsubakiyama, M.; Egi, M.; Wada, Y.; Kita, Y.
Angew. Chem., Int. Ed. 2008, 47, 7673.
(14) Transition-metal-catalyzed syntheses of substituted phenols through
benzannulation by means of ring-closing methathesis have been reported;
see: (a) Yoshida, K.; Imamoto, T. J. Am. Chem. Soc. 2005, 127, 10470. (b)
Yoshida, K.; Horiuchi, S.; Iwadate, N.; Kawagoe, F.; Imamoto, T. Synlett
2007, 1561. (c) Yoshida, K.; Narui, R.; Imamoto, T. Chem. Eur. J. 2008,
14, 9706. (d) Yoshida, K.; Kawagoe, F.; Hayashi, K.; Horiuchi, S.; Imamoto,
T.; Yanagisawa, A. Org. Lett. 2009, 11, 515.
(17) Other than the desired phenol product 3ac, the homo-[2 + 2 + 2]
cycloaddition product of 1a was obtained as a by-product in 13% isolated
yield.
(18) An ether-linked 1,6-diyne, possessing methoxycarbonyl groups at
the alkyne termini, failed to react with 2c as a result of its rapid homo-[2
+ 2 + 2] cycloaddition.
(15) A platinum-catalyzed intramolecular reaction of furans with alkynes,
leading to substituted phenols, was reported; see: Martin-Matute, B.;
Ca´rdenas, D. J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2001, 40, 4754.
(19) Isolation and 1H NMR observation of intermediate B have not been
accomplished at the present stage.
1340
Org. Lett., Vol. 11, No. 6, 2009