Synthesis of naphtho[1,8-bc]pyran derivatives and related compounds through hydroxy group directed C-H bond cleavage under rhodium catalysis

Article abstract of DOI:10.1002/asia.200900639

The straightforward and efficient synthesis of naphtho[1,8-bc]pyran derivatives and related polycyclic compounds is achieved by the rhodium-catalyzed oxidative coupling of 1-naphthols or other phenolic and alcoholic substrates with alkynes. In these annul

Full text of DOI:10.1002/asia.200900639

DOI: 10.1002/asia.200900639
Synthesis of NaphthoACHTUNGTRENNUNG
À
through Hydroxy Group Directed C H Bond Cleavage under Rhodium
Catalysis
Satoshi Mochida, Masaki Shimizu, Koji Hirano, Tetsuya Satoh,* and Masahiro Miura*[a]
Abstract: The straightforward and efficient synthesis of naphthoACTHNUTRGNE[UNG 1,8-bc]pyran de-
À
rivatives and related polycyclic compounds is achieved by the rhodium-catalyzed
oxidative coupling of 1-naphthols or other phenolic and alcoholic substrates with
alkynes. In these annulation reactions, the hydroxy groups effectively act as the
Keywords: annulation · C H acti-
vation · fused-ring systems · homo-
geneous catalysis · rhodium
À
key function for the regioselective C H bond cleavage.
Introduction
A naphthoACHTUNGTRENNUNG[1,8-bc]pyran skeleton can be seen in various nat-
urally occurring and synthetic compounds that exhibit a
broad range of interesting biological[1] and optoelectronic
properties.[2] The skeleton has been constructed through a
complicated multistep process. Thus, easier, more general
approaches towards the skeleton are strongly desired.
À
Transition-metal-catalyzed direct C H functionalization
Scheme 1. The rhodium-catalyzed oxidative coupling of aromatic sub-
strates with internal alkynes.
reactions have been significantly developed in recent years
and have enabled various synthetic routes to be shortened
for a range of complex molecules.[3] As an example, we re-
cently disclosed the one-step synthesis of isocoumarin[4] and
isoquinoline derivatives[5] from readily available substrates,
such as benzoic acids and aromatic imines, respectively. As
shown in Scheme 1, these frameworks can be constructed by
the rhodium-catalyzed oxidative coupling with alkynes, in-
substrates. The hydroxy group also acts as the directing
À
group for the aromatic C H bond cleavage at the peri-posi-
tion.[7] Expectedly, some naphtho
[1,8-bc]pyran derivatives
obtained have been found to show solid-state fluorescence.
Furthermore, the couplings of 2-phenylphenol and 9-phenyl-
xanthen-9-ol with alkynes also proceed smoothly by means
À
volving regioselective C H bond cleavage directed by car-
boxyl and imino groups (LH=CO2H, C=NH).
À
During our further study of rhodium-catalyzed oxidative
coupling,[6] it has been revealed that our catalyst system is
of C H cleavage around the hydroxy functions. These new
findings are described herein.
applicable to the one-step construction of the naphthoACHTUNTRGNEUNG[1,8-
bc]pyran skeleton by using 1-naphthols and alkynes as the
Results and Discussion
[a] S. Mochida, M. Shimizu, Dr. K. Hirano, Prof. Dr. T. Satoh,
Prof. Dr. M. Miura
In an initial attempt, 1-naphthol (1a) (1 mmol) was treated
with diphenylacetylene (2a) (0.5 mmol) in the presence of
[Cp*RhCl2]2 (0.005 mmol) and CuACTHNUTRGNEU(NG OAc)2·H2O (0.025 mmol)
(OAc=acetate) in o-xylene at 1408C (bath temperature) for
6 h under air (Cp*=h5-pentamethylcyclopentadienyl). As a
result, an oxidative coupling product, 2,3-diphenylnaphtho-
Department of Applied Chemistry
Faculty of Engineering, Osaka University
Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-7362
E-mail: satoh@chem.eng.osaka-u.ac.jp
miura@chem.eng.osaka-u.ac.jp
AHCTUNGTREG[NNUN 1,8-bc]pyran (3a), was formed in 64% yield (Table 1,
entry 1). Decreasing the reaction temperature to 120 and
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200900639.
Chem. Asian J. 2010, 5, 847 – 851
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 847

FULL PAPERS
Table 1. Reaction of 1-naphthol (1a) with diphenylacetylene (2a).[a]
Entry
T [8C]
Yield [%][b]
1
2
3
140
120
100
80
64
73
73(70)
57
50
4
5[c]
100
[a] The reaction of 1a (1 mmol) with 2a (0.5 mmol) was conducted with
[{Cp*RhCl2}2] (0.005 mmol) and Cu(OAc)2·H2O (0.025 mmol) in o-xylene
(2.5 mL) under air for 6 h. [b] Yield determined by GC. The value in pa-
rentheses indicates the yield after purification. [c] 1a (0.5 mmol) and 2a
(1 mmol) were used.
AHCTUNGTRENNUNG
Scheme 2. The reaction of 1-naphthols and analogues 1a–e with alkynes
2a–g.
Table 2. Reaction of 1-naphthols and analogues 1 with alkynes 2.[a]
Entry
1
2
Conditions
Product
Yield [%][b]
1008C somewhat improved the product yield (Table 1, en-
tries 2 and 3). At 808C, however, the yield was reduced
(Table 1, entry 4). Under the conditions using an excess
amount of 2a ([1a]=0.5 mmol, [2a]=1 mmol), the yield of
3a was significantly lower (Table 1, entry 5).
1
2
3
4
5
1a
1a
1a
1a
1a
2b
2c
2d
2e
2 f
A
A
A
A
A
3b: R=4-MeC6H4
3c: R=4-MeOC6H4
3d: R=4-ClC6H4
3e: R=nPr
(68)
(74)
(65)
61 (54)
58 (49)
Under the conditions for entry 3 of Table 1 (conditions A:
CuACHTUNGTRENNUNG(OAc)2·H2O (0.025 mmol) in o-xylene (2.5 mL) under
air), the couplings of various 1-naphthols and related hy-
droxy compounds 1a–e with alkynes 2a–g were examined
(Scheme 2 and Table 2). Methyl, methoxy, and chloro-substi-
tuted diphenylacetylenes 2b–d reacted with 1a to form the
3 f: R=n-C7H15
corresponding 2,3-diarylnaphthoACTHUNTGRNEUNG[1,8-bc]pyrans 3b–d in 65–
6
7
1b
1c
2a
2a
A
A
60 (52)
42 (41)
74% yield (Table 2, entries 1–3). Similarly, 2,3-dialkylnaph-
thopyrans 3e and 3 f were also obtained from the reactions
of 1a with 4-octyne (2e) and 8-hexadecyne (2 f), respective-
ly (Table 2, entries 4 and 5). 5-Methoxy- (1b) and 5-trifluor-
oacetylamino- (1c) 1-naphthols underwent the coupling with
2a to form 6-substituted 2,3-diphenylnaphthopyrans 3g and
3h (Table 2, entries 6 and 7).
Treatment of 4-hydroxycoumarin (1d), which possesses a
À
similar peri C H bond to those of 1-naphthols, with 2a
under conditions A did not give any coupling product
(Table 2, entry 8).[8] When using conditions B (conditions B:
with a stoichiometric amount of CuACTHNUTRGEN(UNG OAc)2·H2O (1 mmol) in
DMF (2.5 mL) under N2), the desired coupling product 3i
was obtained in 74% yield (Table 2, entry 9). The reactions
of 1d with 2c and bis(4-tert-butylphenyl)acetylene (2g) pro-
8
9
10
11
1d
1d
1d
1d
2a
2a
2c
2g
A
B
B
B
0
3i: R=Ph
74 (70)
77 (73)
48 (46)
3j: R=4-MeOC6H4
3k: R=4-(tBu)C6H4
Abstract in Japanese:
12
1e
2a
B
96 (92)
[a] The reaction of 1 (1 mmol) with 2 (0.5 mmol) was conducted with
[{Cp*RhCl2}2] (0.005 mmol) at 1008C for 6-8 h. Conditions A: with Cu-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
termined by GC. The value in parentheses indicates the yield after purifi-
cation.
848
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Chem. Asian J. 2010, 5, 847 – 851

Synthesis of NaphthoACHTUNGTRENNUNG[1,8-bc]pyran Derivatives
ceeded similarly to give 3j and 3k, respectively (Table 2, en-
tries 10 and 11). 4-Hydroxy-1-methylquinolin-2-one (1e)
also underwent the coupling with 2a under conditions B to
our catalyst system. Among several substrates employed, 2-
phenylphenol (4) was found to undergo the oxidative cou-
pling with 2a. In this case, these substrates were coupled in
the ratio of 1:2, in contrast to the 1:1 coupling of 1 with 2.
Thus, treatment of 4 (0.5 mmol) with 2a (0.5 mmol) in the
produce
1-methyl-5,6-diphenylpyranoACTHUNGETRNNU[G 2,3,4-de]quinolin-2-
one (3l) in 96% yield (Table 2, entry 12).
Some tricyclic products 3 obtained above showed solid-
state fluorescence in a range of 410–560 nm (see the Sup-
porting Information). Notably, 3c exhibited a relatively
strong emission compared to a typical emitter, Coumarin
153, by a factor of 2.1 (lemis =484 nm, A versus B in
Figure 1).
presence of [Cp*RhCl2]2 (0.005 mmol) and CuACTHNUGETRNNU(G OAc)2·H2O
(0.025 mmol) in o-xylene at 1208C (bath temperature) for
8 h under air gave product 5 in 9% yield (Table 3, entry 1).
À
Similar 1:2 oxidative coupling, accompanied by double C H
bond cleavages, was also observed in our previous work on
the reaction of phenylazoles, such as 1-phenylpyrazole with
Table 3. Reaction of 2-phenylphenol (4) with diphenylacetylene (2a).[a]
Entry
Cu
(OAc)2·H2O [mmol]
T [oC]
Yield [%][b]
1[c]
2
3
0.025
0.5
0.5
0.5
1
120
120
100
150
150
120
9
68
33
54
57
81 (72)
4
Figure 1. The fluorescence spectra of 3c (A) and Coumarin 153 (B) in
the solid-state upon excitation at 421 nm.
5
6[d]
0.5
[a] The reaction of 4 (0.5 mmol) with 2a (0.5 mmol) was conducted with
[{Cp*RhCl2}2] (0.005 mmol) in o-xylene (2.5 mL) under N2 for 6–8 h.
[b] GC yield based on the amount of 2a used. The value in parentheses
indicates the yield after purification. [c] Under air. [d] KI (0.5 mmol) was
added.
A plausible mechanism for the reaction of 1-naphthol
(1a) with alkynes 2 is illustrated in Scheme 3, in which neu-
tral ligands are omitted for clarity. Coordination of the phe-
nolic oxygen to an RhIIIX3 species gives a rhodium
(III)
alkynes.[6c] The yield of 5 was improved to 68% by using a
À
naphtholate A. Directed C H rhodation to form a rhodacy-
cle intermediate B is then followed by alkyne insertion and
reductive elimination to form a naphthopyran 3. The result-
ing RhIX species is oxidized by the copper(II) salt to regen-
erate RhIIIX3. Under air, CuI species may also be reoxidized
to CuII.
stoichimetric amount of CuACHTUNGETRNNU(G OAc)2·H2O (0.5 mmol) under
N2 (Table 3, entry 2). Both decrease and increase of the re-
action temperature reduced the yield of 5 (Table 3, entries 3
and 4). Further increase of the amount of CuACTHUNGTRNEUNG(OAc)2·H2O to
1 mmol at 1508C did not improved the product yield
(Table 3, entry 5). Finally, addition of KI (0.5 mmol) was
found to increase the yield up to 81% (Table 3, entry 6).[9]
Not only such phenolic substrates 1 and 4 but also a terti-
ary alcohol, 9-phenylxanthen-9-ol (6), underwent the oxida-
tive coupling with diarylacetylenes 2a–d involving regiose-
As described above, the hydroxy group can act as a good
anchor for directed C H bond cleavage by Rh species,
such as A to B in Scheme 3. Therefore, we next examined
the reactions of other phenolic and alcoholic substrates with
III
À
À
lective C H bond cleavage at its 1-position to form the cor-
responding annulated products. First, 6 (0.5 mmol) was
treated with 2a (0.5 mmol) in the presence of [Cp*RhCl2]2
(0.005 mmol),
(C5H2Ph4: 0.02 mmol), and CuAHCTNUGTRENNNUG
1,2,3,4-tetraphenyl-1,3-cyclopentadiene
(OAc)2·H2O (1 mmol) in o-
xylene at 1608C (bath temperature) for 8 h under N2. As a
result, pyranoxanthene 7a was produced in 18% yield
(Table 4, entry 1). Without C5H2Ph4, the reaction did not
take place at all (Table 4, entry 2). The catalyst system,
[RhClACHTNUGTREN(UNG cod)]2/C5H2Ph4 (cod=1,5-cyclooctadiene), gave the
significantly better yield of 7a (72%) than [Cp*RhCl2]2/
C5H2Ph4 (Table 4, entry 3 versus entry 1). As a ligand,
C5H2Ph4 was found to be more effective than 1,2,3,4,5-pen-
taphenyl-1,3-cyclopentadiene (C5HPh5) and 1,2,4-triphenyl-
Scheme 3. A plausible mechanism for the reaction of 1a with alkyne 2.
Chem. Asian J. 2010, 5, 847 – 851
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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849

T. Satoh, M. Miura et al.
FULL PAPERS
Table 4. Reaction of 9-phenylxanthen-9-ol (6) with diarylacetylene 2a–
d.[a]
Conclusions
In summary, we have demonstrated that the oxidative cou-
pling of 1-naphthols with internal alkynes can be performed
in the presence of a rhodium/copper catalyst system under
air to selectively give the corresponding naphthoACTHNUTRGNE[UNG 1,8-bc]pyr-
À
an derivatives accompanied by C H bond cleavage at the
peri position. Using similar catalyst systems, 2-phenylphenol
and 9-phenylxanthen-9-ol can also be coupled with alkynes
in 1:2 and 1:1 ratios, respectively. Some of the fused polycyc-
lic products exhibit intense fluorescence in the solid state.
Entry
2
Rh catalyst
[{Cp*RhCl2}2]
[{Cp*RhCl2}2]
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
Ligand
Product, Yield [%][b]
1
2
3
4
2a
2a
2a
2a
2a
2a
2a
2b
2c
2d
G
C5H2Ph4
–
7a, 18
–, 0
7a, 72
7a, 21
7a, 61
7a, 20
7a, 83 (77)
7b, 82 (72)
7c, (76)
7d, (46)
E
E
N
C5H2Ph4
C5HPh5
C5H3Ph3
C5H2Ph4
C5H2Ph4
C5H2Ph4
C5H2Ph4
C5H2Ph4
Experimental Section
R
E
5
R
E
General
6[c]
7[d]
8[d]
9[d]
10[d]
N
E
1H and 13C NMR spectra were recorded at 400 and 100 MHz, for CDCl3
solutions, respectively. MS data were obtained by using electron ioniza-
tion (EI). GC analysis was carried out by using a silicon OV-17 column
(i.d. 2.6 mmꢁ1.5 m) or a CBP-1 capillary column (i.d. 0.5 mmꢁ25 m).
GC-MS analysis was carried out using a CBP-1 capillary column (i.d.
0.25 mmꢁ25 m). The structures of all products were unambiguously de-
termined by using 1H and 13C NMR spectroscopy with the aid of NOE,
COSY, HMQC, and HMBC experiments.
G
C
T
ACHTUNGTRENNUNG
T
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
[a] The reaction of 6 (0.5 mmol) with 2 (0.5 mmol) was conducted with
Rh catalyst (0.005 mmol), ligand (0.02 mmol), and Cu(OAc)2·H2O
(1 mmol) in o-xylene (2.5 mL) under N2 at 1608C for 6–8 h. [b] Yield de-
termined by GC. The value in parentheses indicates the yield after purifi-
cation. [c] At 1408C. [d] 6 (1 mmol) was used.
AHCTUNGTRENNUNG
Diarylacetylenes 2b–d,g,[11] naphthols 1b,c,[7e] and C5H3Ph3 (1,2,4-triphen-
yl-1,3-cyclopentadiene)[12] were prepared according to published proce-
dures. Other starting materials and reagents were commercially available.
1
Copies of the H- and 13C NMR spectra of 3a–l, 5, and 7a–d are given in
the Supporting Information.
1,3-cyclopentadiene (C5H3Ph3) (Table 4, entries 3–5) for
which steric factors may be important. At 1408C, the yield
decreased (Table 4, entry 6). The best result was obtained if
an excess amount of 6 was used, the yield being enhanced to
83% (Table 4, entry 7). Under similar conditions, 6 reacted
with substituted diphenylacetylenes 2b–d to afford the cor-
responding pyranoxanthenes 7b–d (Table 4, entries 8–10).
Previously, we reported that related acyclic tertiary alco-
hols, triarylmethanols, underwent the oxidative coupling
with alkynes in the presence of a similar Rh/Cu catalyst
Synthesis
General Procedure for Oxidative Coupling of 1-Naphthols and Analogues
with Internal Alkynes
Under Conditions A: To a 20 mL two-necked flask were added ArOH 1
(1 mmol), alkyne 2 (0.5 mmol), [{Cp*RhCl2}2] (0.005 mmol, 3 mg), Cu-
A
ternal standard, and o-xylene (2.5 mL). The resulting mixture was stirred
under air at 1008C (bath temperature) for 6–8 h.
Under conditions B: To a 20 mL two-necked flask were added ArOH 1
(1 mmol), alkyne 2 (0.5 mmol), [{Cp*RhCl2}2] (0.005 mmol, 2.5 mg), Cu-
À
À
system via successive C H and C C bond cleavages to
afford 1,2,3,4-tetrasubstituted naphthalenes as 1:2 coupling
products.[6d] In the reactions of 6, however, only trace
amounts of the 1:2 coupling products were detected by
GCMS. The present reaction appears to proceed via a
seven-membered rhodacycle intermediate C’, generated in a
manner similar to that in the reaction of 1a (C in
A
nal standard, and DMF (2.5 mL). The resulting mixture was stirred under
N2 at 1008C (bath temperature) for 6 h. GC and GCMS analyses of the
mixture confirmed formation of 3. The product was also isolated by chro-
matography on silica gel using hexane-ethyl acetate. The solid obtained
was recrystallized from hexane/ethyl acetate. Characterization data of
products are summarized in the Supporting Information.
À
Scheme 3). Then, C O reductive elimination seems to occur
in preference to b-carbon elimination to selectively form 7
(Scheme 4). The latter may be suppressed, owing to the ri-
gidity of tetracyclic C’, in which the interaction between the
Rh center and ipso-aromatic carbon seems to be difficult.[10]
Acknowledgements
This work was partly supported by Grants-in-Aid from the Ministry of
Education, Culture, Sports, Science and Technology, Japan and the
Kurata Memorial Hitachi Science and Technology Foundation.
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850
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Chem. Asian J. 2010, 5, 847 – 851

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[8] Even in DMF, the reaction of 1d did not proceed at all under the
aerobic conditions. Thus, the use of a stoichiometric amount of the
copper salt was essential for the efficient production of 3i.
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Raven, J. Chem. Soc. Dalton Trans. 1986, 1613.
À
[10] The C H bond cleavage at the first step seems to be directed not on
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Received: November 13, 2009
Published online: February 23, 2010
Chem. Asian J. 2010, 5, 847 – 851
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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