Palladium-catalyzed aryl C(sp2)-H bond hydroxylation of 2-arylpyridine using TBHP as oxidant

Article abstract of DOI:10.1021/acs.joc.5b00167

An efficient synthesis of phenols via Pd-catalyzed, pyridyl-directed homogeneous hydroxylation of the aryl C-H bond was developed, in which tert-butyl hydroperoxide was used as the sole oxidant. The method had a broad group tolerance and was available for

Full text of DOI:10.1021/acs.joc.5b00167

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Note
Palladium-Catalyzed Aryl C(sp2)–H Bond
Hydroxylation of 2-Arylpyridine Using TBHP as Oxidant
Jiawei Dong, Ping Liu, and Peipei Sun
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b00167 • Publication Date (Web): 09 Feb 2015
Downloaded from http://pubs.acs.org on February 10, 2015
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Palladium-Catalyzed Aryl C(sp2)–H Bond Hydroxylation of
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2-Arylpyridine Using TBHP as Oxidant
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Jiawei Dong,a Ping Liu,a,b and Peipei Sun*a,b
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aJiangsu Key Laboratory of Biofunctional Materials, Jiangsu Provincial Key Laboratory of
Material Cycle Processes and Pollution Control, College of Chemistry and Materials Science,
Nanjing Normal University, Nanjing 210097, China
bJiangsu Collaborative Innovation Center of Biomedical Functional Materials, Nanjing 210023,
China
sunpeipei@njnu.edu.cn
N
N
Pd(OAc)2
TBHP
H
OH
DCE
Ar
Ar
O bond formation
Direct
24 examples, yield up to 88%
C
ABSTRACT: An efficient synthesis of phenols via Pd-catalyzed, pyridyl-directed homogeneous
hydroxylation of aryl C−H bond was developed, in which tert-butyl hydroperoxide (TBHP) was
used as the sole oxidant. The method had a broad group tolerance and was available for both
electron-rich and electron-deficient substrates. The reaction of a series of 2-arylpyridine
derivatives gave the ortho-hydroxylation products in moderate to good yields.
As a class of important compounds, phenols are naturally abundant. Besides of their application in
organic synthesis, phenols are major constituents of many biological and natural compounds and
almost ubiquitously exist in the structural organization of plants and animals.1 Phenolic
compounds were generally industrially synthesized by multi-step procedures as represented by the
cumene process.1b In view of green and sustainable chemistry as well as in economic terms, a
direct C(sp2)–H bond hydroxylation for phenol synthesis with an inexpensive oxidant and without
any sacrificial reactant is desired. Transition metal-catalyzed C(sp2)–H bond functionalization
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provided the possibility for this transformation.1a,2 Though the transition metal-catalyzed C–O
bond formation is considered to be more difficult compared with C–C and some other C–
heteroatom bonds,3 there have been many successful examples in this regard. A range of
palladium-catalyzed alkoxylation of C(sp2)–H bond were developed.4 Moreover, a series of
encouraging progresses on the direct oxidation of aryl C(sp2)–H bond catalyzed by transition
metals to form phenols also have been achieved in recent years. These hydroxylation
regioselectively took place at the ortho-position of aromatic rings directed by the carbonyl,5 ester,6
carbamyl,7 carbamate,8 carboxyl,9 acylamino,10 phosphate11 and some azacyclic groups.12 After the
ortho-hydroxylation of aryl moiety of 2-arylpyridines using Pd(OAc)2/oxone in
PEG-3400/t-BuOH reported by Kim et al,12a Jiao et al12b developed a novel PdCl2 and NHPI
(N-hydroxyphthalimide) cocatalyzed aromatic C(sp2)–H bond hydroxylation of 2-phenylpyridines
recently, in which molecular oxygen was used as a heterogeneous oxidant for this transformation.
Patel et al12e also obtained a hydroxylation product of 2-phenylpyridine by using tert-butyl
hydroperoxide (TBHP) as the oxidant in their study on the palladium-catalyzed acylation of
2-phenylpyridines, but the further study was not done. In our continuous study on the
palladium-catalyzed oxidative coupling reaction, we found that the peroxide could be as an
effective homogeneous oxidant for the C–H bond functionalization.13 We herein present an
efficient method for the synthesis of phenols via Pd−catalyzed, pyridyl-directed homogeneous
hydroxylation of aryl C−H bond using TBHP as the sole oxidant.
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We initiated our study by employing 2-phenylpyridine (1a) as the reactant in the presence of
catalyst and TBHP (Table 1). Without palladium catalyst, the reaction could not take place at all
(entry 1). Thus, Pd(OAc)2, PdCl2, Pd(PPh3)2Cl2, and Pd(CH3CN)2Cl2 were tested for this
transformation, in which Pd(OAc)2 was proved to be most effective (entries 5, 14−16). The
oxidation reaction could be catalyzed by 5 mol % Pd(OAc)2 to give the hydroxylation product
2-(pyridin-2-yl)phenol (2a) in 58% yield using 4.0 equiv TBHP as the oxidant in DCE
(1,2-dichloroethane) (entry 3). The amount of the oxidant had an evident effect to this oxidation.
In the absence of TBHP, no desired product was detected (entry 2). Increasing TBHP to 6.0 equiv
led to a higher yield of 82% (entry 5); further raising it to 7.0 equiv did not improve the yield
evidently (entry 6). Another influence factor to this reaction was the solvent. In DCE, the reaction
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proceeded smoothly and gave a highest yield; in TCE (1,1,2,2-tetrachloroethane), the
hydroxylation product with a lower yield of 79% was obtained (entry 8). In CH3CN, dioxane or
DMF, however, only trace desired product was found (entries 9−11). The reaction temperature was
also crucial. The appropriate temperature was proved to be 115 °C. Raising the temperature to
125 °C failed to further increase the yield (entry 13), but at 100 °C, only 43% yield was obtained
(entry 12). It is noticeable that when the reaction proceeded in nitrogen atmosphere, the similar
result was obtained as that in air (entry 17).
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Table 1. Optimization of Reaction Conditionsa
Pd catalyst
TBHP
N
N
OH
solvent
1a
2a
entry
1
catalyst (mol %)
-
TBHP (equiv)
solvent
DCE
yield (%)
0
6.0
-
2
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (10)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
PdCl2 (5)
DCE
0
3
4.0
5.0
6.0
7.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
DCE
58
4
DCE
77
5
DCE
82
6
DCE
83
7
DCE
86
8
TCE
79
9
CH3CN
dioxane
DMF
DCE
trace
trace
trace
43
10
11
12b
13c
14
15
DCE
80
DCE
62
Pd(PPh3)2Cl2 (5)
DCE
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Pd(CH3CN)2Cl2 (5)
Pd(OAc)2 (5)
6.0
6.0
DCE
DCE
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85
17d
6
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aUnless otherwise specified, the reactions were carried out in a sealed tube in the presence of
2-phenypyridine (1a, 0.3 mmol), solvent (1 mL), catalyst, and TBHP under air atmosphere at
115 °C for 20 h. bAt 100 °C. cAt 125 °C. dIn N2 atmosphere.
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With the optimal conditions in hand, a series of 2-arylpyridines were tested and the results
are summarized in Table 2. The meta- or para-halogenated substrates were well-compatible with
the process and afforded corresponding hydroxylated products in good yields (2c−2h). However,
2-(2-fluorophenyl)pyridine gave the desire product in a relatively lower yield of 55% (2b), which
might be because of the steric effect. Arenes containing other electron-withdrawing groups also
afforded the expected product with good yields, except the case of carbonyl or ester-containing
compounds which only gave moderate yields (2n, 2o). Interestingly, the reaction of
2-(naphthalen-2-yl)pyridine exactly gave a β-hydroxylation product (2w), which might also be
attributed to the less steric hindrance of its β-position. The large conjugated reactant
benzo[h]quinolone also gave a 10-hydroxylated product in 79% yield (2x). Some substrates with
electron-donating groups seemed to be disadvantageous to the reaction. For example, the moderate
yields were obtained from methoxy-, ethyl- or n-pentyl substituted 2-phenylpyridines (2p, 2s, 2t),
and the exact reason is not clear. In general, formation of the dihydroxylation product was not
observed, and for meta-substituted substrates the hydroxylation proceeded at the less steric
hindered position with high regioselectivity. It must be pointed out that when 7 mmol (1.09 g) 1a
was used, the product 2a was still achieved with a yield of 79%, which demonstrated the practical
utility of the present method.
Table 2. Palladium-Catalyzed Hydroxylation of 2-Arylpyridines with TBHPa
N
N
Pd(OAc)2 (5 mol %)
TBHP (6.0 equiv)
OH
DCE, 115 o
C
R
R
1
2
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N
N
N
N
F
OH
OH
OH
OH
6
F
7
8
9
F
2a, 82%, (79%)b
2b, 55%
2c, 72%
2e, 68%
2d, 70%
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N
OH
Br
2g, 76%
2i, 84%
2f, 84%
2h, 73%
2j, 88%
N
OH
O2N
2m, 87%
2k, 85%
2l, 85%
2o, 69%
2n, 64%
N
OH
Et
2q, 80%
2p, 51%
2r, 73%
2s, 59%
2t, 62%
2x, 79%
2u, 83%
2w, 61%
2v, 65%
aReaction conditions: 2-arylpyridine (1, 0.3 mmol), Pd(OAc)2 (5 mol %) and TBHP (6.0 equiv) in
DCE (1 mL) under air atmosphere at 115 °C for 20 h. bThe reaction of 1a (7 mmol, 1.09 g) under
the standard reaction conditions.
A control experiment was also carried out (Scheme 1). A radical-trapping reagent
2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was added in the reaction mixture of 1a under the
established reaction conditions. The results showed that in the presence of 2 equiv TEMPO, the
yield of 2a was reduced to 30%, while the amount of TEMPO was increased to 4 equiv, a yield
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lower than 10% was obtained (Scheme 1). The obvious inhibitory effect of TEMPO indicated that
the radicals maybe existed in this transformation.
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Scheme 1. Effect of TEMPO to Reaction
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Pd(OAc)2 (5 mol %)
TBHP (6.0 equiv)
TEMPO
DCE, 115 oC
N
N
OH
2a
1a
TEMPO: 2 equiv
yield 30%
10%
yield
4 equiv
As that mentioned in our optimization to reaction conditions, when the reaction proceeded in
nitrogen atmosphere, the similar result was obtained as that in air (Table 1, entry 17), which
revealed that TBHP was the sole hydroxyl source. Based on our experimental results and related
reports,14 we proposed a possible mechanism for this direct hydroxylation of aryl C−H bond
(Scheme 2). Initially, the chelation-assisted C−H activation at the ortho-position of directing group
with Pd(OAc)2 to form a Pd(II) intermediate A. Homolysis of TBHP gave the HO• and t-BuO•,13
which could abstract a hydrogen radical from HOAc, then released AcO•, followed by oxidative
addition of HO• and AcO• to form Pd(IV) intermediate B. Finally, reductive elimination of B gave
the product 2a and regenerated the Pd(II) species.
Scheme 2. Plausible Reaction Mechanism
N
N
1a
OH
2a
Pd(OAc)2
HOAc
OAc
Ac
O
Pd
N
N
Pd OAc
OH
2
HOAc
B
A
t
-BuOH
+
OH OBu-
t
TBHP
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In summary, a simple method for the synthesis of phenols by Pd(OAc)2 catalyzed,
pyridyl-directed aryl sp2 C−H bond activation using TBHP as the solo oxidant and without any
ligand has been explored. Various substituents on the aryl ring, including some coupling reaction
sensitive group (Cl, Br) tolerated the reaction and gave the hydroxylation products in moderate to
good yields.
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Experimental Section
General
All reactions were run in air. All reagents were commercially available and were used without
further purification. NMR spectra were recorded at 400 MHz (1H) and 100 MHz (13C{1H}) using
TMS as an internal standard. Chemical shifts are given relative to CDCl3 (7.28 ppm for 1H NMR,
77.16 ppm for 13C{1H} NMR). The following abbreviations were used to describe
peak splitting patterns when appropriate: s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet, dd = doublet of doublets, dt = doublet of triplets, ddd = doublet of doublet of doublets,
td = triplet of doublets, brs = broad singlet. Melting points are uncorrected. For the HRMS
measurements, Q-TOF analyzer was used.
General Experimental Procedures for Palladium-catalyzed ortho-Hydroxylation of
2-Arylpyridines and Characterizations
A mixture of 2-arylpyridines 1 (0.3 mmol), Pd(OAc)2 (3.4 mg, 5 mol %) and TBHP (0.25 mL, 6.0
equiv, 70% aqueous solution) combined in 1,2-dichloroethane (DCE, 1 mL) was sealed in a 25 mL
tube with a Teflon lined cap. The tube was then placed in an oil bath, stirred and heated at 115 °C
for 20 h. After cooling to room temperature, the reaction mixture was quenched with brine and
extracted with dichloromethane (30 mL × 3). The combined organic layer was dried with
anhydrous Na2SO4 and the solvent was removed under vacuum. The crude product was purified
over a column of silica gel (eluant: hexane/ethyl acetate) to afford the desired product 2.
2-(Pyridin-2-yl)phenol (2a)12b Yellow oil (42.1 mg, 82% yield). H NMR (400 MHz, CDCl3) δ
1
14.34 (brs, 1H), 8.52 (d, J = 4.5 Hz, 1H), 7.93 (d, J = 8.3 Hz, 1H), 7.89–7.76 (m, 2H), 7.35–7.28
(m, 1H), 7.28–7.23 (m, 1H), 7.04 (dd, J = 8.2, 1.0 Hz, 1H), 6.95–6.87 (m, 1H); 13C{1H} NMR
(100 MHz, CDCl3) δ 160.0, 157.8, 145.8, 137.8, 131.5, 126.2, 121.5, 119.1, 118.8, 118.6.
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3-Fluoro-2-(pyridin-2-yl)phenol (2b) Yellow solid (31.2 mg, 55% yield). Mp: 55-57 C. 1H NMR
(400 MHz, CDCl3) δ 14.86 (brs, 1H), 8.61–8.53 (m, 1H), 8.19 (d, J = 8.4 Hz, 1H), 7.93–7.85 (m,
1H), 7.32 (ddd, J = 7.5, 5.0, 1.0 Hz, 1H), 7.24 (td, J = 8.3, 6.4 Hz, 1H), 6.86 (dt, J = 8.3, 1.0 Hz,
1H), 6.67 (ddd, J = 12.7, 8.2, 1.2 Hz, 1H); 13C{1H} NMR (101 MHz, CDCl3) δ 162.0 (d, J = 251.2
Hz), 161.3 (d, J = 5.6 Hz), 154.5, 145.4, 138.1, 130.9 (d, J = 12.7 Hz), 124.7 (d, J = 21.1 Hz),
122.0, 114.2 (d, J = 2.8 Hz), 108.7 (d, J = 11.4 Hz), 106.2 (d, J = 25.0 Hz); HRMS-ESI (m/z):
calcd for C11H8FNONa [M + Na]+ 212.0482, found 212.0484.
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4-Fluoro-2-(pyridin-2-yl)phenol (2c)12b Yellow solid (40.9 mg, 72% yield). Mp: 76-77 C. H
NMR (400 MHz, CDCl3) δ 13.98 (brs, 1H), 8.61–8.50 (m, 1H), 7.87 (ddd, J = 13.4, 10.0, 4.9 Hz,
2H), 7.47 (dd, J = 9.9, 2.9 Hz, 1H), 7.30 (ddd, J = 6.7, 5.0, 1.5 Hz, 1H), 7.11–6.93 (m, 2H);
13C{1H} NMR (100 MHz, CDCl3) δ 156.7 (d, J = 2.8 Hz), 156.0 (d, J = 1.6 Hz), 155.7 (d, J =
236.3 Hz), 146.0, 138.1, 122.1, 119.5 (d, J = 7.9 Hz), 119.3, 118.8 (d, J = 7.2 Hz), 118.4 (d, J =
23.2 Hz), 111.8 (d, J = 24.3 Hz).
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5-Fluoro-2-(pyridin-2-yl)phenol (2d)12b Yellow solid (39.7 mg, 70% yield). Mp: 109-111 C. H
NMR (400 MHz, CDCl3) δ 14.81 (brs, 1H), 8.56–8.44 (m, 1H), 7.89–7.81 (m, 2H), 7.77 (dd, J =
8.9, 6.5 Hz, 1H), 7.32–7.20 (m, 1H), 6.74 (dd, J = 10.6, 2.6 Hz, 1H), 6.64 (ddd, J = 8.9, 8.0, 2.7
Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.6 (d, J = 250.3 Hz), 162.0 (d, J = 12.9 Hz),
157.2, 145.6, 137.9, 127.5 (d, J = 10.8 Hz), 121.5, 118.8, 115.4 (d, J = 2.8 Hz), 106.3 (d, J = 22.4
Hz), 105.2 (d, J = 23.3 Hz).
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4-Chloro-2-(pyridin-2-yl)phenol (2e) Yellow solid (41.9 mg, 68% yield). Mp: 95-96 C. 1H NMR
(400 MHz, CDCl3) δ 14.34 (brs, 1H), 8.54 (dt, J = 5.0, 1.5 Hz, 1H), 7.92–7.81 (m, 2H), 7.77 (d, J
= 2.5 Hz, 1H), 7.34–7.18 (m, 2H), 6.99 (d, J = 8.8 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ
158.6, 156.6, 146.0, 138.1, 131.2, 125.7, 123.5, 122.1, 120.0, 119.8, 119.2; HRMS-ESI (m/z):
calcd for C11H9ClNO [M + H]+ 206.0367, found 206.0365.
5-Chloro-2-(pyridin-2-yl)phenol (2f)12b Yellow solid (51.8 mg, 84% yield). Mp: 82-83 C. H
NMR (400 MHz, CDCl3) δ 14.70 (brs, 1H), 8.52 (dt, J = 5.0, 1.4 Hz, 1H), 7.91–7.80 (m, 2H), 7.72
(d, J = 8.6 Hz, 1H), 7.33–7.21 (m, 1H), 7.05 (d, J = 2.2 Hz, 1H), 6.90 (dd, J = 8.6, 2.2 Hz, 1H);
13C{1H} NMR (100 MHz, CDCl3) δ 160.8, 157.0, 145.8, 138.0, 136.7, 127.0, 121.8, 119.1, 119.0,
118.6, 117.4.
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4-Bromo-2-(pyridin-2-yl)phenol (2g) Yellow solid (57.0 mg, 76% yield). Mp: 111-114 C. H
NMR (400 MHz, CDCl3) δ 14.22 (brs, 1H), 8.54 (dt, J = 5.0, 1.4 Hz, 1H), 7.92–7.86 (m, 3H), 7.39
(dd, J = 8.8, 2.4 Hz, 1H), 7.34–7.29 (m, 1H), 6.94 (d, J = 8.8 Hz, 1H); 13C{1H} NMR (100 MHz,
CDCl3) δ 159.0, 156.4, 145.9, 138.1, 134.1, 128.7, 122.2, 120.5, 120.4, 119.2, 110.6; HRMS-ESI
(m/z): calcd for C11H8BrNONa [M + Na]+ 271.9681, found 271.9694.
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5-Bromo-2-(pyridin-2-yl)phenol (2h) Yellow solid (54.8 mg, 73% yield). Mp: 67-68 C. 1H NMR
(400 MHz, CDCl3) δ 14.64 (brs, 1H), 8.51 (dt, J = 5.0, 1.4 Hz, 1H), 7.91–7.81 (m, 2H), 7.65 (d, J
= 8.5 Hz, 1H), 7.32–7.25 (m, 1H), 7.22 (d, J = 2.0 Hz, 1H), 7.04 (dd, J = 8.5, 2.1 Hz, 1H); 13C{1H}
NMR (100 MHz, CDCl3) δ 160.8, 157.0, 145.8, 138.0, 127.1, 124.9, 122.0, 121.9, 121.6, 119.0,
117.7; HRMS-ESI (m/z): calcd for C11H8BrNONa [M + Na]+ 271.9681, found 271.9691.
2-(Pyridin-2-yl)-4-(trifluoromethoxy)phenol (2i) Yellow solid (64.3 mg, 84% yield). Mp: 62-64 oC.
1H NMR (400 MHz, CDCl3) δ 14.26 (brs, 1H), 8.55 (dt, J = 5.0, 1.4 Hz, 1H), 7.94–7.82 (m, 2H),
7.65 (d, J = 2.7 Hz, 1H), 7.35–7.29 (m, 1H), 7.22–7.17 (m, 1H), 7.04 (d, J = 9.0 Hz, 1H); 13C{1H}
NMR (100 MHz, CDCl3) δ 158.6, 156.5, 145.9, 141.0 (d, J = 2.0 Hz), 138.1, 122.3, 120.7 (q, J =
257.0 Hz), 119.6, 119.3, 119.0, 119.0; HRMS-ESI (m/z): calcd for C12H9F3NO2 [M + H]+
256.0580, found 256.0584.
2-(Pyridin-2-yl)-5-(trifluoromethoxy)phenol (2j) Yellow solid (67.4 mg, 88% yield). Mp: 68-70 oC.
1H NMR (400 MHz, CDCl3) δ 14.69 (brs, 1H), 8.51 (dt, J = 5.1, 1.4 Hz, 1H), 7.89–7.83 (m, 2H),
7.80 (d, J = 8.8 Hz, 1H), 7.32–7.25 (m, 1H), 6.90 (dd, J = 2.4, 1.1 Hz, 1H), 6.77 (ddd, J = 8.8, 2.4,
1.1 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 161.4, 156.8, 151.2 (d, J = 1.7 Hz), 145.8, 138.0,
127.2, 121.9, 120.4 (q, J = 257.7 Hz), 119.1, 117.3, 110.8, 110.4; HRMS-ESI (m/z): calcd for
C12H9F3NO2 [M + H]+ 256.0580, found 256.0584.
2-(Pyridin-2-yl)-4-(trifluoromethyl)phenol (2k) Yellow solid (60.1 mg, 85% yield). Mp: 88-89 oC.
1H NMR (400 MHz, CDCl3) δ 14.77 (brs, 1H), 8.56 (d, J = 4.7 Hz, 1H), 8.07 (d, J = 1.4 Hz, 1H),
7.99 (d, J = 8.3 Hz, 1H), 7.95–7.88 (m, 1H), 7.56 (dd, J = 8.6, 1.9 Hz, 1H), 7.35 (ddd, J = 7.2, 5.1,
0.9 Hz, 1H), 7.12 (d, J = 8.6 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 162.7, 156.5, 145.8,
138.3, 128.2 (q, J = 3.5 Hz), 124.5 (q, J = 272.1 Hz), 123.6 (q, J = 3.9 Hz), 122.4, 120.9 (q, J =
32.7 Hz), 119.3, 119.1, 118.4; HRMS-ESI (m/z): calcd for C12H9F3NO [M + H]+ 240.0631, found
240.0627.
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2-(Pyridin-2-yl)-5-(trifluoromethyl)phenol (2l)12b Yellow solid (60.1 mg, 85% yield). Mp: 107-108
oC. 1H NMR (400 MHz, CDCl3) δ 14.51 (brs, 1H), 8.57 (d, J = 4.8 Hz, 1H), 7.97 (d, J = 8.2 Hz,
1H), 7.94–7.87 (m, 2H), 7.39–7.32 (m, 1H), 7.29 (s, 1H), 7.17–7.09 (m, 1H); 13C{1H} NMR (100
MHz, CDCl3) δ 160.1, 156.5, 146.0, 138.2, 132.9 (q, J = 32.6 Hz), 126.6, 123.8 (q, J = 272.4 Hz),
122.6, 121.5, 119.6, 115.8 (q, J = 3.9 Hz), 115.0 (q, J = 3.8 Hz).
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4-Nitro-2-(pyridin-2-yl)phenol (2m) Yellow solid (56.4 mg, 87% yield). Mp: 212-213 C. H
NMR (400 MHz, CDCl3) δ 15.65 (brs, 1H), 8.82 (d, J = 2.7 Hz, 1H), 8.59 (ddd, J = 5.0, 1.7, 0.9
Hz, 1H), 8.22 (dd, J = 9.1, 2.7 Hz, 1H), 8.09 (d, J = 8.3 Hz, 1H), 8.00 (ddd, J = 8.3, 7.6, 1.8 Hz,
1H), 7.42 (ddd, J = 7.5, 5.1, 1.1 Hz, 1H), 7.10 (d, J = 9.1 Hz, 1H); 13C{1H} NMR (100 MHz,
CDCl3) δ 166.1, 155.8, 145.7, 139.8, 138.7, 126.9, 123.0, 122.7, 119.5, 119.3, 118.1; HRMS-ESI
(m/z): calcd for C11H8N2O3Na [M + Na]+ 239.0427, found 239.0429.
1-(3-Hydroxy-4-(pyridin-2-yl)phenyl)ethanone (2n) Yellow solid (40.9 mg, 64% yield). Mp:
116-117 C. 1H NMR (400 MHz, CDCl3) δ 14.48 (brs, 1H), 8.56 (ddd, J = 5.0, 1.7, 0.9 Hz, 1H),
o
7.98 (d, J = 8.3 Hz, 1H), 7.94–7.84 (m, 2H), 7.58 (d, J = 1.8 Hz, 1H), 7.50 (dd, J = 8.3, 1.8 Hz,
1H), 7.34 (ddd, J = 7.4, 5.0, 1.1 Hz, 1H), 2.62 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 197.8,
160.0, 156.7, 146.1, 139.2, 138.1, 126.3, 122.6, 122.5, 119.8, 119.0, 118.0, 26.8; HRMS-ESI (m/z):
calcd for C13H11NO2Na [M + Na]+ 236.0682, found 236.0687.
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Ethyl 3-hydroxy-4-(pyridin-2-yl)benzoate (2o) Yellow solid (50.4 mg, 69% yield). Mp: 94-95 C.
1H NMR (400 MHz, CDCl3) δ 14.41 (brs, 1H), 8.55 (d, J = 4.9 Hz, 1H), 7.97 (d, J = 8.3 Hz, 1H),
7.92–7.83 (m, 2H), 7.70 (d, J = 1.7 Hz, 1H), 7.57 (dd, J = 8.3, 1.7 Hz, 1H), 7.32 (ddd, J = 7.4, 5.0,
0.9 Hz, 1H), 4.39 (q, J = 7.1 Hz, 2H), 1.41 (t, J = 7.1 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3)
δ 166.2, 159.7, 156.9, 146.0, 138.0, 132.9, 126.1, 122.4, 119.8, 119.8, 119.5, 61.1, 14.3;
HRMS-ESI (m/z): calcd for C14H13NO3Na [M + Na]+ 266.0788, found 266.0793.
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5-Methoxy-2-(pyridin-2-yl)phenol (2p) Yellow oil (30.8 mg, 51% yield). H NMR (400 MHz,
CDCl3) δ 14.66 (brs, 1H), 8.45 (d, J = 5.0 Hz, 1H), 7.83–7.76 (m, 2H), 7.70 (d, J = 8.8 Hz, 1H),
7.21–7.13 (m, 1H), 6.56 (d, J = 2.6 Hz, 1H), 6.49 (dd, J = 8.8, 2.6 Hz, 1H), 3.84 (s, 3H); 13C{1H}
NMR (100 MHz, CDCl3) δ 162.4, 161.9, 157.8, 145.5, 137.6, 127.2, 120.5, 118.3, 112.1, 106.6,
102.2, 55.3; HRMS-ESI (m/z): calcd for C12H12NO2 [M + H]+ 202.0863, found 202.0860.
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4-Methyl-2-(pyridin-2-yl)phenol (2q) Yellow oil (44.4 mg, 80% yield). H NMR (400 MHz,
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CDCl3) δ 14.01 (brs, 1H), 8.55–8.48 (m, 1H), 7.93 (d, J = 8.4 Hz, 1H), 7.88–7.79 (m, 1H), 7.61 (d,
J = 1.7 Hz, 1H), 7.25 (ddd, J = 7.4, 5.0, 1.0 Hz, 1H), 7.14 (dd, J = 8.2, 1.9 Hz, 1H), 6.96 (d, J =
8.3 Hz, 1H), 2.36 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 157.9, 157.7, 145.9, 137.7, 132.4,
127.7, 126.3, 121.4, 119.0, 118.4, 20.8; HRMS-ESI (m/z): calcd for C12H11NONa [M + Na]+
208.0733, found 208.0735.
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5-Methyl-2-(pyridin-2-yl)phenol (2r)12b Yellow oil (40.6 mg, 73% yield). H NMR (400 MHz,
CDCl3) δ 14.19 (brs, 1H), 8.50 (d, J = 4.8 Hz, 1H), 7.89 (d, J = 8.3 Hz, 1H), 7.86–7.79 (m, 1H),
7.68 (d, J = 8.1 Hz, 1H), 7.25–7.19 (m, 1H), 6.87 (s, 1H), 6.73 (d, J = 8.1 Hz, 1H), 2.34 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3) δ 159.9, 158.0, 145.8, 142.1, 137.7, 125.9, 121.1, 119.9, 118.9,
118.7, 116.2, 21.4.
5-Ethyl-2-(pyridin-2-yl)phenol (2s) Yellow oil (35.3 mg, 59% yield). 1H NMR (400 MHz, CDCl3)
δ 14.24 (brs, 1H), 8.52 (ddd, J = 5.1, 1.8, 0.9 Hz, 1H), 7.91 (d, J = 8.4 Hz, 1H), 7.84 (ddd, J = 8.3,
7.4, 1.8 Hz, 1H), 7.73 (d, J = 8.1 Hz, 1H), 7.24 (ddd, J = 7.3, 5.1, 1.1 Hz, 1H), 6.95–6.88 (m, 1H),
6.78 (dd, J = 8.1, 1.8 Hz, 1H), 2.66 (q, J = 7.6 Hz, 2H), 1.28 (t, J = 7.6 Hz, 3H); 13C{1H} NMR
(100 MHz, CDCl3) δ 160.0, 157.9, 148.5, 145.7, 137.8, 126.1, 121.1, 118.9, 118.8, 117.6, 116.4,
28.8, 15.1; HRMS-ESI (m/z): calcd for C13H14NO [M + H]+ 200.1070, found 200.1068.
5-Pentyl-2-(pyridin-2-yl)phenol (2t) Yellow oil (44.9 mg, 62% yield). 1H NMR (400 MHz, CDCl3)
δ 14.36 (brs, 1H), 8.51 (ddd, J = 5.0, 1.8, 1.0 Hz, 1H), 7.93–7.86 (m, 1H), 7.82 (ddd, J = 8.4, 7.4,
1.8 Hz, 1H), 7.72 (d, J = 8.2 Hz, 1H), 7.22 (ddd, J = 7.4, 5.0, 1.1 Hz, 1H), 6.89 (d, J = 1.6 Hz, 1H),
6.76 (dd, J = 8.1, 1.7 Hz, 1H), 2.67–2.52 (m, 2H), 1.74–1.61 (m, 2H), 1.41–1.32 (m, 4H), 0.92 (t,
J = 7.0 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 159.9, 158.0, 147.2, 145.8, 137.7, 125.9,
121.1, 119.3, 118.8, 118.2, 116.4, 35.8, 31.5, 30.7, 22.6, 14.0; HRMS-ESI (m/z): calcd for
C16H20NO [M + H]+ 242.1539, found 242.1535.
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5-(tert-Butyl)-2-(pyridin-2-yl)phenol (2u) Yellow oil (56.6 mg, 83% yield). H NMR (400 MHz,
CDCl3) δ 14.30 (brs, 1H), 8.51 (ddd, J = 5.0, 1.8, 0.9 Hz, 1H), 7.90 (d, J = 8.4 Hz, 1H), 7.82 (ddd,
J = 8.3, 7.4, 1.8 Hz, 1H), 7.75 (d, J = 8.4 Hz, 1H), 7.22 (ddd, J = 7.3, 5.0, 1.1 Hz, 1H), 7.09 (d, J =
2.0 Hz, 1H), 6.98 (dd, J = 8.4, 2.0 Hz, 1H), 1.36 (s, 9H); 13C{1H} NMR (100 MHz, CDCl3) δ
159.7, 157.8, 155.4, 145.8, 137.7, 125.8, 121.1, 118.8, 116.3, 116.2, 115.5, 34.8, 31.1; HRMS-ESI
(m/z): calcd for C15H17NONa [M + Na]+ 250.1202, found 250.1202.
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4-(Pyridin-2-yl)-[1,1'-biphenyl]-3-ol (2v)12b Yellow solid (48.2 mg, 65% yield). Mp: 156-157 C.
1H NMR (400 MHz, CDCl3) δ 14.45 (brs, 1H), 8.54 (ddd, J = 5.0, 1.8, 0.9 Hz, 1H), 7.95 (d, J =
8.3 Hz, 1H), 7.91–7.80 (m, 2H), 7.70 (dq, J = 2.8, 1.7 Hz, 2H), 7.52–7.44 (m, 2H), 7.43–7.37 (m,
1H), 7.34 (d, J = 1.9 Hz, 1H), 7.29–7.23 (m, 1H), 7.20 (dd, J = 8.3, 1.9 Hz, 1H); 13C{1H} NMR
(100 MHz, CDCl3) δ 160.3, 157.6, 145.9, 144.2, 140.2, 137.8, 128.8, 127.8, 127.0, 126.6, 121.5,
119.1, 117.8, 117.7, 116.8.
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3-(Pyridin-2-yl)naphthalen-2-ol (2w) Yellow solid (40.5 mg, 61% yield). Mp: 150-151 C. H
NMR (400 MHz, CDCl3) δ 14.05 (brs, 1H), 8.59 (d, J = 4.4 Hz, 1H), 8.35 (s, 1H), 8.18 (d, J = 8.1
Hz, 1H), 7.94 (t, J = 7.4 Hz, 1H), 7.83 (d, J = 8.1 Hz, 1H), 7.69 (d, J = 8.3 Hz, 1H), 7.45 (t, J =
7.2 Hz, 1H), 7.40 (s, 1H), 7.37–7.29 (m, 2H); 13C{1H} NMR (100 MHz, CDCl3) δ 157.3, 156.6,
145.8, 138.4, 135.9, 128.4, 127.5, 127.4, 127.2, 126.0, 123.3, 122.2, 121.3, 120.6, 112.3;
HRMS-ESI (m/z): calcd for C15H11NONa [M + Na]+ 244.0733, found 244.0735.
Benzo[h]quinolin-10-ol (2x)4a Yellow solid (46.3 mg, 79% yield). Mp: 102-104 oC. 1H NMR (400
MHz, CDCl3) δ 14.96 (s, 1H), 8.85 (dd, J = 4.7, 1.7 Hz, 1H), 8.27 (dd, J = 8.1, 1.7 Hz, 1H), 7.83
(d, J = 8.9 Hz, 1H), 7.67–7.61 (m, 2H), 7.58 (dd, J = 8.0, 4.7 Hz, 1H), 7.44 (dd, J = 7.9, 0.9 Hz,
1H), 7.30–7.26 (m, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 159.4, 148.3, 145.0, 136.3, 135.0,
129.9, 129.2, 126.3, 124.6, 120.8, 118.1, 115.9, 114.0.
ASSOCIATED CONTENT
■ AUTHOR INFORMATION
Corresponding Author
*E-mail: sunpeipei@njnu.edu.cn.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work was supported by the National Natural Science Foundation of China (Project 21272117)
and the Priority Academic Program Development of Jiangsu Higher Education Institutions. The
authors also thank Mr. Zilie Liu for the determination of HRMS.
Supporting Information
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Copies of 1H NMR and 13C NMR spectra for all products. This material is available free of charge
via the Internet at http://pubs.acs.org.
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