Rhodium-catalyzed oxidative coupling of triarylmethanols with internal alkynes via successive C-H and C-C bond cleavages

Article abstract of DOI:10.1021/jo7022087

(Chemical Equation Presented) The rhodium-catalyzed oxidative coupling of triarylmethanols with internal alkynes effectively proceeds in a 1:2 manner via cleavage of C-H and C-C bonds to produce the corresponding naphthalene derivatives. Addition of trior tetraphenylcyclopentadiene as a ligand is crucial for the reaction to occur efficiently.

Full text of DOI:10.1021/jo7022087

catalyst to give biaryls via cleavage of the ortho C-H or ipso
C-C bond selectively depending on the substrates and catalysts
employed, in which coordination of their alcoholic oxygen to
the metal is the key (Scheme 1).3 Furthermore, under appropriate
conditions, the alcohols also couple with diphenylacetylene
accompanied by C-C bond cleavage to form 1:1 coupling
products, 1,1,2-triphenylethenes.4 In the course of our further
study of the catalytic intermolecular coupling of aromatic
substrates with alkynes,5 it has been revealed that the alcohols
efficiently react with internal alkynes in a 1:2 manner under
oxidative conditions using Rh as a principal catalyst5a,d,6 in place
of Pd to produce naphthalene derivatives via successive C-H
and C-C bond cleavages. This represents a new example of
aromatic homologation by the coupling of ArX and two alkyne
molecules.7 The findings are described herein.
Rhodium-Catalyzed Oxidative Coupling of
Triarylmethanols with Internal Alkynes via
Successive C-H and C-C Bond Cleavages
Toshihiko Uto, Masaki Shimizu, Kenji Ueura,
Hayato Tsurugi, Tetsuya Satoh,* and Masahiro Miura*
Department of Applied Chemistry, Faculty of Engineering,
Osaka UniVersity, Suita, Osaka 565-0871, Japan
satoh@chem.eng.osaka-u.ac.jp;
miura@chem.eng.osaka-u.ac.jp
ReceiVed October 11, 2007
SCHEME 1. Coupling of r,r-Disubstituted Arylmethanols
with Aryl Halides via C-H or C-C Bond Cleavage
The rhodium-catalyzed oxidative coupling of triarylmetha-
nols with internal alkynes effectively proceeds in a 1:2
manner via cleavage of C-H and C-C bonds to produce
the corresponding naphthalene derivatives. Addition of tri-
or tetraphenylcyclopentadiene as a ligand is crucial for the
reaction to occur efficiently.
When triphenylmethanol (1a) (0.25 mmol) was treated with
diphenylacetylene (2a) (0.5 mmol) in the presence of [Cp*RhCl2]2
(0.005 mmol) and Cu(OAc)2‚H2O (0.5 mmol) in o-xylene at
170 °C (bath temperature) for 4 h under N2, 1,2,3,4-tetraphe-
nylnaphthalene (3a) was formed in 16% yield (entry 1 in Table
Transition-metal-catalyzed organic reactions via C-H1 and
C-C1c,h,2 bond cleavage have attracted much attention from the
atom-economic and chemoselective points of view, and various
catalytic processes involving different modes to activate the
relatively inert bonds have been developed. Among the most
promising activation strategies is to utilize the proximate effect
by coordination of a functional group in a given substrate to
the metal center of a catalyst. As such examples, we recently
reported that a number of R,R-disubstituted arylmethanols react
with aryl chlorides and bromides in the presence of a palladium
(3) (a) Terao, Y.; Wakui, H.; Nomoto, N.; Satoh, T.; Miura, M.; Nomura,
M. J. Org. Chem. 2003, 68, 5236. (b) Terao, Y.; Wakui, H.; Satoh, T.;
Miura, M.; Nomura, M. J. Am. Chem. Soc. 2001, 123, 10407. (c) Wakui,
H.; Kawasaki, S.; Satoh, T.; Miura, M.; Nomura, M. J. Am. Chem. Soc.
2004, 126, 8658.
(4) Terao, Y.; Nomoto, M.; Satoh, T.; Miura, M.; Nomura, M. J. Org.
Chem. 2004, 69, 6942.
(5) (a) Ueura, K.; Satoh, T.; Miura, M. J. Org. Chem. 2007, 72, 5362.
(b) Katagiri, T.; Tsurugi, H.; Funayama, A.; Satoh, T.; Miura, M. Chem.
Lett. 2007, 36, 830. (c) Horita, A.; Tsurugi, H.; Funayama, A.; Satoh, T.;
Miura, M. Org. Lett. 2007, 9, 2231. (d) Ueura, K.; Satoh, T.; Miura, M.
Org. Lett. 2007, 9, 1407. (e) Shibata, K.; Satoh, T.; Miura, M. Org. Lett.
2005, 7, 1781. (f) Funayama, A.; Satoh, T.; Miura, M. J. Am. Chem. Soc.
2005, 127, 15354. (g) Satoh, T.; Ogino, S.; Miura, M.; Nomura, M. Angew.
Chem., Int. Ed. 2004, 43, 5063. (h) Kawasaki, S.; Satoh, T.; Miura, M;,
Nomura, M. J. Org. Chem. 2003, 68, 6836. (i) Yasukawa, T.; Satoh, T.;
Miura, M.; Nomura, M. J. Am. Chem. Soc. 2002, 124, 12680. (j) Pivsa-
Art, S.; Satoh, T.; Miura, M.; Nomura, M. Chem. Lett. 1997, 823. (k)
Kokubo, K.; Matsumasa, K.; Miura, M.; Nomura, M. J. Org. Chem. 1996,
61, 6941.
(6) Catalytic reactions involving â-carbon elimination in Rh(I) alcoho-
lates: (a) Reference 5c. (b) Reference 5f. (c) Nishimura, T.; Katoh, T.;
Hayashi, T. Angew. Chem., Int. Ed. 2007, 46, 4937. (d) Matsuda, T.; Makino,
M.; Murakami, M. Org. Lett. 2004, 6, 1257. For examples of retro-allylation
of homoallyl alcohols, see: (e) Jang, M.; Hayashi, S.; Hirano, K.; Yorimitsu,
H.; Oshima, K. Tetrahedron Lett. 2007, 48, 4003. (f) Takada, Y.; Hayashi,
S.; Hirano, K.; Yorimitsu, H.; Oshima, K. Org. Lett. 2006, 8, 2515.
(7) Related naphthalene synthesis by the 1:2 coupling of ArX with
internal alkynes. X ) CrPh2: (a) Whitesides, G. M.; Ehmann, W. J. J. Am.
Chem. Soc. 1970, 92, 5625. (b) Herwig, W.; Metlesics, W.; Zeiss, H. J.
Am. Chem. Soc. 1959, 81, 6203. X ) I. (c) Reference 5h. (d) Wu, G.;
Rheingold, A. L.; Feib, S. L.; Heck, R. F. Organometallics 1987, 6, 1941.
(e) Sakakibara, T.; Tanaka, Y.; Yamasaki, T.-I. Chem. Lett. 1986, 797. X
) COCl: (f) Reference 5i. X ) CO2H. (g) Reference 5a. o-Dihalobenzenes.
(h) Huang, W.; Zhou, X.; Kanno, K.-I.; Takahashi, T. Org. Lett. 2004, 6,
2429.
(1) Reviews: (a) Alberico, D.; Scott, M. E.; Lautens, M. Chem. ReV.
2007, 107, 174. (b) Satoh, T.; Miura, M. Chem. Lett. 2007, 36, 200. (c)
Satoh, T.; Miura, M. J. Synth. Org. Chem. 2006, 64, 1199. (d) Conley, B.
L.; Tenn, W. J., III; Young, K. J. H.; Ganesh, S. K.; Meier, S. K.; Ziatdinov,
V. R.; Mironov, O.; Oxgaard, J.; Gonzales, J.; Goddard, W. A., III; Periana,
R. A. J. Mol. Catal. A. 2006, 251, 8. (e) Miura, M.; Satoh, T. In Handbook
of C-H Transformations; Dyker, G., Ed.; Wiley-VCH: Weinheim, 2005;
Vol. 1, p 223. (f) Miura, M.; Satoh, T. Top. Organomet. Chem. 2005, 14,
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3, 47. (n) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879.
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10.1021/jo7022087 CCC: $40.75 © 2008 American Chemical Society
Published on Web 12/05/2007
298
J. Org. Chem. 2008, 73, 298-300

TABLE 1. Reaction of Triphenylmethanol (1a) with
Diphenylacetylene (2a)a
TABLE 2. Reaction of Triarylmethanols 1a-d with
Diarylacetylenes 2a-ca
entry
Rh catalyst
ligand
yield of 3ab
1
2c
3
4
5
[Cp*RhCl2]2
RhCl3‚3H2O
[RhCl(cod)]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
RhCl3‚3H2O
Rh(acac)3
16
tr
tr
56
53
51
10
2
entry
1
R1
2
R2
product, % yieldb
C5H2Ph4
C5H3Ph3
C5HPh5
C5HMe5
C5H2Ph4
C5H2Ph4
C5H2Ph4
C5H2Ph4
C5H2Ph4
C5H2Ph4
C5H2Ph4
1c
2
1b
1c
1d
1a
1a
OMe
Me
Cl
H
H
2a
2a
2a
2b
2c
H
H
H
Me
Cl
3b, 88 (65)
3c, (85)
3d, 61 (58)
3e, 87 (63)
3f, (86)
6
7
3d
4
8d
9c
10c
11
12
13e
14e
5
2
2
22
a Reaction conditions: [1]/[2]/[[RhCl(cod)]2]/[C5H2Ph4]/[Cu(OAc)2‚H2O]
) 0.5:0.5:0.005:0.02:0.5 (in mmol), in o-xylene (2.5 mL) at 170 °C for 4
h under N2. b GC yield based on the amount of 2 used. Value in parentheses
indicates yield after purification. c For 6 h. d [Cp*RhCl2]2 was used in place
of [RhCl(cod)]2.
[RhCl(C2H4)2]2
[RhCl(cod)]2
[Cp*RhCl2]2
[RhCl(cod)]2
82
79(77)
quant(99)
a Reaction conditions: [1a]/[2a]/[[Rh catalyst]/[ligand]/[Cu(OAc)2‚H2O]
) 0.25:0.5:0.005:0.02:0.5 (in mmol), in o-xylene (2.5 mL) at 170 °C for 4
h under N2. b GC yield based on the amount of 2a used. Value in parentheses
indicates yield after purification. c With Rh catalyst (0.01 mmol). d In DMAc
(2.5 mL). e With 1a (0.5 mmol).
TABLE 3. Reaction of Triarylmethanols 1a-d with
Dialkylacetylenes 5a,ba
1, Cp* ) η5-pentamethylcyclopentadienyl). Trace amounts of
3a were obtained in the cases using RhCl3‚H2O and [RhCl-
(cod)]2 (cod ) 1,5-cyclooctadiene) in place of [Cp*RhCl2]2.
Interestingly, it was found that the addition of a multiply
phenylated cyclopentadiene as a ligand (0.02 mmol) significantly
improves the reaction efficiency. Thus, the reaction with a
catalyst system of [Cp*RhCl2]2/C5H2Ph4 afforded 3a in 56%
yield (entry 4). While C5H3Ph3 and C5HPh5 showed comparable
effects (entries 5 and 6), use of C5HMe5 decreased the yield
(entry 7). The reaction in a polar solvent such as DMAc was
sluggish (entry 8). Even with C5H2Ph4 as the ligand, RhCl3‚
H2O, Rh(acac)3, and [RhCl(C2H4)2]2 showed low activities
(entries 9-11). Finally, the combination of [RhCl(cod)]2 with
C5H2Ph4 was found to be the catalyst system of choice, and the
yield of 3a was enhanced up to 82% (entry 12). Furthermore,
under conditions using an excess amount of 1a (0.5 mmol) in
the presence of [RhCl(cod)]2/C5H2Ph4, 3a was formed quanti-
tatively (entry 14).
product,
entry
1
R1
5
R2
Rh catalyst
ligand
% yieldb
1
2
3
4
5
6
7
1a
H
5a C7H15 [RhCl(cod)]2 C5H2Ph4 6a, 45
[RhCl(cod)]2 C5H3Ph3 6a, 68
[Cp*RhCl2]2 C5H3Ph3 6a, 87 (63)
1b OMe 5a C7H15 [Cp*RhCl2]2 C5H3Ph3 6b, 57 (47)
1c Me
1d Cl
1a
5a C7H15 [Cp*RhCl2]2 C5H3Ph3 6c, 68 (56)
5a C7H15 [Cp*RhCl2]2 C5H3Ph3 6d, 91 (89)
H
5b Pr
[Cp*RhCl2]2 C5H3Ph3 6e, 59 (57)
a Reaction conditions:[1]/[5]/[Rh catalyst]/[ligand]/[Cu(OAc)2‚H2O] )
0.5:0.5:0.005:0.02:0.5 (in mmol), in o-xylene (2.5 mL) at 170 °C for 4-6
h under N2. b GC yield based on the amount of 5 used. Value in parentheses
indicates yield after purification.
SCHEME 2. Reaction of Triphenylmethanol (1a) with
Bis(4-methoxyphenyl)acetylene (2d)
Table 2 summarizes the results for the coupling employing a
series of triarylmethanols and diarylacetylenes with use of the
[RhCl(cod)]2/C5H2Ph4 catalyst system. The reaction of alcohols
1b-d with 2a proceeded efficiently to produce 6-methoxy-,
-methyl-, and -chloro-1,2,3,4-tetraphenylnaphthalenes 3b-d in
61-88% yields (entries 1-3).8 In the reaction of 1d with 2a,
the catalyst system with [Cp*RhCl2]2 gave a somewhat better
result compared with that with [RhCl(cod)]2. 4,4′-Disubstituted
diphenylacetylenes 2b and 2c also reacted with 1a to give the
corresponding 1,2,3,4-tetraarylnaphthalenes 3e and 3f in good
yields (entries 4 and 5). In contrast to these alkynes, bis(4-
methoxyphenyl)acetylene (2d) was found to react with 1a in a
1:1 manner with retaining the C-C bond of 1a to give an
isochromene derivative 4 in 24% yield, along with a small
amount of the expected tetraarylnaphthalene (Scheme 2).
Under similar conditions using [RhCl(cod)]2/C5H2Ph4, 1a also
reacted with an aliphatic alkyne, 8-hexadecyne (5a) to afford
1,2,3,4-tetraheptylnaphthalene (6a) in 45% yield (entry 1 in
Table 3). For this reaction, C5H3Ph3 functioned as a more
(8) Reactions of (4-methylphenyl)- and (4-fluorophenyl)diphenylmetha-
nols with 2a under similar conditions gave mixtures of 6-substituted and
unsubstituted 1,2,3,4-tetraphenylnaphthalenes (6-Me/6-H ) ca. 1:1, 6-F/
6-H ) ca. 1:4).
J. Org. Chem, Vol. 73, No. 1, 2008 299

SCHEME 3. Plausible Mechanism for the Reaction of 1a
with 2 or 5
selectively give the corresponding 1:2 coupling products,
naphthalene derivatives accompanied by successive C-H and
C-C bond cleavages. Rh-catalyst systems for oxidative C-C
coupling reactions have been less explored than those with
Pd.5a,d,11,12 The present catalyst systems and related ones are
expected to be applicable to other coupling reactions. Work is
underway toward further development of the catalysis.
Experimental Section
General Procedure for Oxidative Coupling of Triarylmetha-
nols with Internal Alkynes. To a 20 mL two-necked flask were
added triarylmethanol 1 (0.25 or 0.5 mmol), internal alkyne 2 or 5
(0.5 mmol), Rh catalyst (0.005 or 0.01 mmol), ligand (0.02 mmol),
Cu(OAc)2‚H2O (0.5 mmol, 100 mg), 1-methylnaphthalene (ca. 50
mg) as internal standard, and o-xylene or DMAc (2.5 mL). The
resulting mixture was stirred under N2 at 170 °C (bath temperature)
for 4-6 h. GC and GC-MS analyses of the mixtures confirmed
formation of 3, 4, or 6. The product was also isolated by evaporation
of solvents in vacuo and chromatography on silica gel using
hexane-ethyl acetate.
efficient ligand rather than C5H2Ph4 to improve the yield of 6a
to 68% (entry 2). Moreover, [Cp*RhCl2]2 showed higher activity
than [RhCl(cod)]2 in combination with C5H3Ph3. Thus, with the
catalyst system of [Cp*RhCl2]2/C5H3Ph3, 6a was obtained in
87% yield (entry 3). Other alcohols 1b-d reacted with 5a in
the presence of [Cp*RhCl2]2/C5H3Ph3 to afford the correspond-
ing naphthalenes 6b-d in good to excellent yields (entries 4-6).
Under similar conditions, 4-octyne (5b) also underwent the
coupling with 1a to form 1,2,3,4-tetrapropylnaphthalene (6e)
(entry 7).9
A plausible mechanism for the reaction of triphenylmethanol
(1a) with alkyne 2 or 5 is illustrated in Scheme 3, in which
neutral ligands are omitted. Coordination of the alcoholic oxygen
to a Rh(III)X3 species gives a rhodium(III) alcoholate A. Then,
ortho-rhodation to form a rhodacycle intermediate B, alkyne
insertion, and â-carbon elimination successively occur to
produce a rhodacycle D with libration of Ph2CO. The subsequent
second alkyne insertion and reductive elimination take place to
form naphthalene 3 or 6. The resulting Rh(I)X species may be
oxidized in the presence of the copper(II) salt to regenerate Rh-
(III)X3. While the stoichiometric10 and catalytic reactions5c,f,6
involving â-carbon elimination in Rh(I) alcoholates have been
reported, the process via that in Rh(III) alcoholates is very rare.
In the reaction of 1a with 2d (R ) 4-MeOC6H4) (Scheme 2),
C-O reductive elimination from the seven-membered rhoda-
cycle intermediate C5a,d may be faster than â-carbon elimination
to release isochromene 4 rather than the expected naphthalene.
In summary, we have demonstrated that the oxidative
coupling of triarylmethanols with internal alkynes can be
performed in the presence of a rhodium catalyst, a tri- or
tetraphenylcyclopentadiene ligand, and a copper oxidant to
1,2,3,4-Tetraphenylnaphthalene (3a) (Entry 14 in Table 1).
Following the general procedure allowed the product to be isolated
as a slightly yellow solid (107 mg, 99%): mp 206-208 °C (lit.5h
1
mp 209-210 °C); H NMR (400 MHz, CDCl3) δ 6.82-6.86 (m,
10H), 7.17-7.32 (m, 10H), 7.38-7.40 (m, 2H), 7.63-7.65 (m, 2H);
13C NMR (100 MHz, CDCl3) δ 125.3, 125.8, 126.4, 126.5, 127.0,
127.5, 131.3 (overlapped), 132.0, 138.4, 138.9, 139.6, 140.5; MS
m/z 432 (M+).
1,2,3,4-Tetraheptylnaphthalene (6a) (Entry 3 in Table 3).
Following the general procedure allowed the product to be isolated
as a colorless oil (82 mg, 63%): 1H NMR (270 MHz, CDCl3) δ
7.99-7.97 (m, 2H), 7.40-7.38 (m, 2H), 3.02-2.99 (m, 4H), 2.74-
2.72 (m, 4H), 1.68-1.25 (m, 40H), 0.93-0.89 (m, 12H); 13C NMR
δ 136.9, 134.2, 131.1, 124.5, 124.4, 31.92, 31.89, 31.6, 31.3, 30.52,
30.46, 30.4, 30.3, 29.2, 29.1, 22.7 (overlapped), 14.13, 14.11;
HRMS m/z (M+) calcd for C38H64 520.5008, found 520.4996.
Acknowledgment. This work was partly supported by
Grants-in-Aid from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
Supporting Information Available: Standard experimental
procedure and characterization data of products. This material is
available free of charge via the Internet at http://pubs.acs.org.
JO7022087
(11) Rh-catalyzed oxidative coupling of unactivated aromatic compounds
with alkenes has been reported: (a) Matsumoto, T.; Periana, R. A.; Taube,
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H. Chem. Lett. 2000, 1064.
(12) For examples of rhodium-catalyzed aerobic oxidation, see: (a)
Fazlur-Rahman, A. K.; Tsai, J.-C.; Nicholas, K. M. J. Chem. Soc., Chem.
Commun. 1992, 1334. (b) Bressan, M.; Morvillo, A. Inorg. Chim. Acta
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734. (d) Mimoun, H.; Perez-Machirant, M. M.; Se´re´e de Roch, I. J. Am.
Chem. Soc. 1978, 100, 5437.
(9) Ir-Catalyzed reactions of benzoic acid with 5a and 5b gave the
corresponding tetraalkylnaphthalenes in low yields (10-20%). See reference
5a.
(10) Zhao, P.; Christopher, D. I.; Hartwig, J. F. J. Am. Chem. Soc. 2006,
128, 3124.
300 J. Org. Chem., Vol. 73, No. 1, 2008