Palladium-catalyzed cross-coupling reactions of 2-diazonaphthoquinones with arylboronic acids

Article abstract of DOI:10.1016/j.tetlet.2011.02.047

Palladium-catalyzed cross-coupling reactions of 2-diazonaphthoquinones and arylboronic acids proceeded by the treatment with Pd(OAc)₂ in acetic acid to afford 2-aryl-1-naphthols.

Full text of DOI:10.1016/j.tetlet.2011.02.047

Tetrahedron Letters 52 (2011) 1931–1933
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Palladium-catalyzed cross-coupling reactions of 2-diazonaphthoquinones
with arylboronic acids
⇑
Mitsuru Kitamura , Rie Sakata, Tatsuo Okauchi
Department of Applied Chemistry, Kyushu Institute of Technology, 1-1 Sensuicho, Tobata, Kitakyushu 804-8550, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium-catalyzed cross-coupling reactions of 2-diazonaphthoquinones and arylboronic acids pro-
ceeded by the treatment with Pd(OAc)2 in acetic acid to afford 2-aryl-1-naphthols.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 10 January 2011
Revised 8 February 2011
Accepted 10 February 2011
Available online 13 February 2011
Keywords:
Arylboronic acids
Cross-coupling
Diazo compounds
Diazonaphthoquinones
Palladium catalysis
Introduction of substituents to aromatic compounds is an
important process in organic synthesis. The electrophilic aromatic
substitution reaction is used for this purpose in general.1 For the
synthesis of biaryl compounds, the cross-coupling reaction of aryl
halides/sulfonates derived from the corresponding aryl compounds
is widely used.2
Regioselective arylation of 1-naphthol is one of the difficult is-
sues that remained in the synthesis of the substituted phenol
derivatives. The products, 2-aryl-1-naphthols, are attractive candi-
dates for germicide and fungicide to replace 2-phenylphenol.3
Barton reported that 2-phenyl-1-naphthol could be synthesized
directly from 1-naphthol by the reaction with pentaphenyl
bismuth in 48% yield.4,5 Oi et al. have reported Rh(I)-mediated
coupling of 1-naphthol and bromobenzene, in which a mixture of
2-phenyl and 2,8-diphenyl-1-naphthol was obtained.6 Although
the syntheses of 2-halo-1-naphthol have been reported,7 the
cross-coupling reaction for the synthesis of 2-aryl-1-naphthol has
not been investigated in our knowledge.
Recently, we reported that 2-diazonaphthoquinone could be
regioselectively synthesized from the corresponding 1-naphthols by
the diazo-transfer with 2-azido-1,3-dimethylimidazolinium chloride
(ADMC) 2 (Scheme 1).8,9 We expected that 2-aryl-1-naphthol
derivatives could be synthesized regioselectively if N2 moiety in
2-diazonaphthoquinone 3a was substituted with suitable aryl metal
compounds. That is, we supposed that the Pd(0)-catalyzed coupling
of diazonaphthoquinone with arylboronic acids would proceed
similar to Suzuki–Miyaura coupling10 if the diazonaphthoquinone
behaved like aryl diazonium 3a0.11,12 We became interested in
and thus examined the palladium-catalyzed cross-coupling reaction
of aryl boronic acids with diazonaphthoquinones. In this Letter,
we describe the outcome of this investigation.
We initially attempted to couple diazonaphthoquinone 3a and
p-tolylboronic acid [p-Tol-B(OH)2] (Table 1). First, we examined
the reaction by using an excess amount of p-tolylboronic acid
(1.2 equiv) relative to diazonaphthoquinone in the presence of
Pd(0) catalyst (Runs 1–3) in several solvents (MeOH, CH3CN, and
AcOH); the yields of coupling product 4a were low.
When Pd(OAc)2 was used as a catalyst, the yield of 4a was
greater than when Pd(0) catalyst was used in MeOH, CH3CN, and
AcOH, respectively, and biaryl 5a was formed as a by product (Runs
4–6). Among the solvents, we investigated in the presence of
Pd(OAc)2 (Runs 4–9), the yield of 4a was high in CH3CN and AcOH
–
+
N
N
OH
N
Cl–
Et3N
+
+
MeN
NMe
THF, CH3CN
–20°C, 30 min
80%
1
2
O–
O
+
N2
N2
3a
3a'
⇑
Corresponding author.
E-mail address: kita@che.kyutech.ac.jp (M. Kitamura).
Scheme 1. Synthesis of diazonaphthoquinone 3a.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.02.047

1932
M. Kitamura et al. / Tetrahedron Letters 52 (2011) 1931–1933
Table 1
Table 2
Optimization of the coupling of diazonaphthoquinone 3a and p-Tol-B(OH)2
Pd-catalyzed coupling of diazonaphthoquinone 3a and various aryl boronic acidsa
O
OH
OH
O
Ar-B(OH)2
cat. Pd(OAc)2
KF
p-Tol-B(OH)2
10 mol% Pd cat.
N2
p-Tol
+
Ar
N2
[p-Tol]2
+ Ar2
CH3CO2H
50 °C
3a
Run Pd cat.
4a
5a
Yielda (%)
3a
4
5
Additive Solvent
Conditions
Run
Ar
Ph
Time (h)
Yieldb (%)
4a
5a
4
5
1b
Pd(PPh3)4
—
MeOH
CH3CN
AcOH
rt
3
0
21 h
50 °C
3.5 h
rt
9.5 h
Reflux
1.5 h
50 °C
1 h
1
2
3
4
5
6
7
3
3
3
2
4
5
4
4b
4c
4d
4e
4f
76
56
40
53
25
34
47
5b
5c
5d
5e
5f
Trace
2
0
3
4
16
7
2b
Pd2(dba)3
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
—
8
0
o-MeC6H4
o-MeOC6H4
m-MeOC6H4
p-MeOC6H4
p-CF3C6H4
3b
—
2
0
4b
—
MeOH
CH3CN
AcOH
8
8
4g
4h
5g
5h
1-Naphthyl
5b
—
32
31
6
11
Trace
6
a
Molar ratio: 3a/Ar-B(OH)2/Pd(OAc)2/KF = 1/3/0.1/3.
b
6b
—
50 °C
2 h
Isolated yield.
7b
—
1,4-Dioxane rt
9.5 h
8 was obtained in 4% yield, and naphthalene triol derivative 9 was
8b
—
DMF
60 °C
2 h
rt
2.5 h
50 °C
1 h
50 °C
40 min
50 °C
7 h
2
2
obtained in 51% yield (eq. 2).15
9b
—
Toluene
AcOH
AcOH
AcOH
AcOH
AcOH
trace
43
45
19
67
65
0
3 eq p-Tol-B(OH)2
10 mol% Pd(OAc)2
3 equiv KF
O
OH
10c
11c
12c
13c
14c
—
7
N2
p-Tol
(1)
CH3CO2H
50 °C, 3 h
Pd(OCOCF3)2
PdCl2
—
5
Cl
O
R
3b
—
3
6 (R = Cl): 48%
7 (R = OAc): 20%
Pd(OAc)2
Pd(OAc)2
KF
TBAF
50 °C
3 h
50 °C
8 h
11
10
3 eq p-Tol-B(OH)2
10 mol% Pd(OAc)2
3 equiv. KF
OH
R
N2
(2)
CH3CO2H
50 °C, 3 h
a
b
c
Isolated yield.
Molar ratio: 3a/p-Tol-B(OH)2/M cat. = 1.2/1/0.1.
Molar ratio: 3a/p-Tol-B(OH)2/M cat./additive = 1/3/0.1/3.
OMe
OMe
3c
8 (R = p-Tol ): 4%
9 (R = OAc): 51%
Recently, Wang reported the palladium-catalyzed cross coupling
of acyclic -diazocarbonyl compounds with aryl boronic acid, pro-
(32% and 31%, respectively), and thus, we chose AcOH as the sol-
vent for further study because the reaction media were cleaner
than those when using CH3CN as a solvent. Next, the coupling reac-
tion was examined by using an excess amount of boronic acid rel-
ative to diazonaphthoquinone 3 (Runs 10–14). The yield of 4a was
increased to 43% when 3 equiv of boronic acid was used (Run 10).
As a palladium catalyst, Pd(OCOCF3)2 showed almost the same
ability as Pd(OAc)2, whereas PdCl2 was ineffective (Runs 11 and
12). In Suzuki–Miyaura coupling, the addition of F– is sometimes
effective.13 In the coupling of 3a, the yield of 4a was increased to
67% or 65% by the addition of KF or tetrabutylammonium fluoride
(TBAF), respectively (Runs 13 and 14).
A series of aryl boronic acids were then subjected to the opti-
mized reaction conditions (Table 1, Run 13) with diazonaphthoqui-
none 3a (Table 2). When mono methyl or the non-substituted
phenyl boronic acid was used, the coupling products were
obtained in good yields (Runs 1 and 2).14 In the series of mono-
methoxyphenyl boronic acids (Runs 3–5), the reaction proceeded
smoothly, although a lower yield was observed for the para-
substituted boronic acid (Run 5). The reaction with phenyl boronic
acid having an electron-deficient group, such as a trifluoromethyl
group, proceeded affording the corresponding coupling product
4g, but the yield was not high (Run 6). 1-Naphthyl boronic acid
was used for the coupling reaction (Run 7).
a
posing the Pd(0)–Pd(II) catalytic cycle as the mechanism and palla-
dium carbene complex as a key intermediate.16 In Scheme 2,
possible two reaction mechanisms for the Pd(OAc)2-catalyzed cou-
pling of diazonaphthoquinone 3a and aryl boronic acid in the
presence of acetic acid are depicted. Mechanism A is the general
Suzuki–Miyaura coupling mechanism which is based on Pd(0)–
Pd(II) cycle initiated by the oxidative addition of protonated
diazonaphthoquinone I to Pd(0). Transmetallation between aryl pal-
ladium II and aryl(fluoro)borate proceeded to give diarylpalladium
complex III,13 which underwent a reductive elimination, leading
to form 2-aryl-1-naphthol 4 and the regeneration of Pd(0) catalyst.
Mechanism B is the Pd(II)-catalytic cycle via the migratory insertion
of a palladium carbene complex.16,17 The reaction is initiated by the
transmetallation of aryl boronic acid by the aid of F–10,13 and
Pd(OAc)2 to generate intermediate IV,16 which reacts with diazo-
naphthoquinone 3a to form palladium carbene complex V. Migra-
tory insertion of the aryl group to the carbene carbon occurs,
generating palladium complex VI. Finally, the protonation of acetic
acid to VI affords the coupling product 4 and regenerates Pd(OAc)2.
Because it was more efficient to use of Pd(II) complex than
Pd(0) complex in this reaction, as shown in Table 1, we uphold
Pd(II)-cycle, that is, mechanism B as the reaction mechanism in
the proposed mechanisms. Acetate 9 would be formed by the reac-
tion of 3c and Pd(OAc)2 instead of IV, and the successive migratory
insertion of the acethoxy group to the carbene carbon similar to
aryl group migration as shown V?VI.
Then, the reaction of 4-substituted 2-diazonaphthoquinone
with p-tolyl boronic acid was examined. The reaction of 4-chloro
diazonaphthoquinone 3b proceeded smoothly to give the coupling
products in 68% as a mixture of 6 and 7 (eq. 1). In the reaction of 4-
methoxy diazonaphthoquinone 3c, the expected coupling product
In conclusion, we have demonstrated the first palladium-
catalyzed cross-coupling reaction of diazonaphthoquinone and

M. Kitamura et al. / Tetrahedron Letters 52 (2011) 1931–1933
1933
References and notes
mechanism A: Pd(0)-cycle
Pd(OAc)2
AcO–
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OH
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–
–
AcOB(OH)2
ArB(OH)2
ArB(OH)2
F
F
mechanism B: Pd(II)-cycle
8. Kitamura, M.; Tashiro, N.; Sakata, R.; Okauchi, T. Synlett 2010, 2503.
9. For the reaction with 2-azido-1,3-dimethylimidazolinium salt, see: (a)
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OH
Ar
ArB(OH)2
F–
Pd(OAc)2
–
Ar-B(OH)2
4
F
–
AcOH
AcOB(OH)2
F
OAc
Ar
O
Pd
Ar–Pd–OAc
IV
O
N2
VI
O
OAc
Pd
3a
N2
Ar
V
14. Typical procedure for the Pd-catalyzed coupling of 2-diazonaphthoquinone 3a
and aryl boronic acid (Table 2, Run 1): A acetic acid (2 mL) solution of 2-
diazonaphthoquinone 3a (40.9 mg, 0.24 mmol), 1-naphthyl boronic acid
(88.0 mg, 0.72 mmol), KF 41.9 mg, 0.72 mmol), and Pd(OAc)2 (5.4 mmol,
0.024 mmol) under nitrogen atmosphere was warmed to 50 °C and stirred
for 3 h. After cooling the mixture to room temperature, sat NaHCO3 aq was
added, and the mixture was extracted with CH2Cl2 (ꢀ3). The combined extracts
were washed with brine, dried over anhydrous MgSO4, and evaporated in
vacuo. The residue was purified by flash column chromatography (hexane/
EtOAc = 80/20) to afford cross-coupling product 4b (40.1 mg, 76%) and biaryl
5b (0.2 mg).
15. Diazonaphthoquinone 9 was also obtained in 49% yield by the reaction of 3c in
the absence of p-Tol-B(OH)2 (10 mol % Pd(OAc)2, 3 equiv KF, CH3CO2H, 50 °C,
3 h).
16. Peng, C.; Wang, Y.; Wang, J. J. Am. Chem. Soc. 2008, 130, 1566.
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Commun. 2003, 756; (b) Albéniz, A. C.; Espinet, P.; Manrique, R.; Pérez-Mateo,
Scheme 2. Possible reaction mechanisms.
aryl boronic acid. It provides a novel access to biaryl compounds.
Because 2-diazonaphthoquinone can be regioselectively synthe-
sized from 1-naphthol by diazo-transfer,8 regioselective C-2 aryla-
tion of 1-naphthol was possible in two steps (diazotization then
cross-coupling with aryl boronic acid). Although the reaction
mechanism is unclear, the proposed mechanism, including the
migratory insertion of palladium carbene, is recently recognized
and established.16,17 Further studies on the scope and the mecha-
nism of the reaction are currently in progress.
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Acknowledgments
This work was supported by the Nagase Science Technology
Foundation and a Grant-in-Aid from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan.