Regioselective ortho-hydroxylation of aryl moiety of 2-arylpyridines using Pd(OAc)2/Oxone in PEG-3400/tert-BuOH

Article abstract of DOI:10.1016/j.tetlet.2008.07.141

Regioselective ortho-hydroxylation of aryl moiety of 2-arylpyridines was carried out under the influence of Pd(OAc)₂/Oxone (potassium peroxymonosulfate) in PEG-3400/t-BuOH in moderate yields.

Full text of DOI:10.1016/j.tetlet.2008.07.141

Tetrahedron Letters 49 (2008) 5863–5866
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Regioselective ortho-hydroxylation of aryl moiety of 2-arylpyridines
using Pd(OAc)2/Oxone in PEG-3400/tert-BuOH
*
Sung Hwan Kim, Hyun Seung Lee, Se Hee Kim, Jae Nyoung Kim
Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Regioselective ortho-hydroxylation of aryl moiety of 2-arylpyridines was carried out under the influence
of Pd(OAc)2/Oxone (potassium peroxymonosulfate) in PEG-3400/t-BuOH in moderate yields.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 20 June 2008
Revised 15 July 2008
Accepted 18 July 2008
Available online 29 July 2008
Keywords:
2-Arylpyridines
Hydroxylation
Pd(OAc)2
Oxone
Baylis-Hillman adducts
Recently, palladium-mediated C–H bond activations of 2-aryl-
pyridines and related systems are regarded as one of the hot
topics.1–4 Introductions of various functional groups have been
reported, including alkyls,1 aryls,2 halogens3 and acetoxy group.4
Although many types of functionalizations have been reported,
direct hydroxylation is unprecedented to the best of our knowl-
edge.1–5
Very recently we reported an efficient synthetic method of
poly-substituted pyridines from Baylis-Hillman adducts via the
[3+2+1] annulation protocol.6 Further functionalization of the
CH3
Bn
Pd(OAc)2 (10 mol%)
PhI(OAc)2 (2.0 equiv)
N
OAc
AcOH/Ac2O, 100-110 o
C
Ph
4a (61%)
(For 3a, entry 1 in Table 1)
OAc O
Ph
CH3
CH3
CH3
N
CH3
N
Bn
Bn
1. K2CO3, DMF
2. NH4OAc, AcOH
Pd(OAc)2 (10 mol%)
Oxone (2.0 equiv)
1
N
OMe
OH
Bn
+
+
R1
Ref. 6
MeOH, reflux
(For 3a, entry 4 in Table 1)
Ph
Ph
R2
O
7a (3%)
5a (11%)
CH3
3
R2
a: R1 = Ph, R2 = Ph
R1
b: R1 = 4-MeOC6H4, R2 = 4-MeOC6H4
c: R1 = 4-ClC6H4, R2 = Ph
2
Bn
Pd(OAc)2 (10 mol%)
Oxone (2.0 equiv)
N
O
d: R1 = 4-MeC6H4, R2 = Ph
e: R1 = 2,5-Me2C6H3, R2 = Ph
f: R1 = 2,4-Me2C6H3, R2 = Ph
g: R1 = 3,4-Me2C6H3, R2 = Ph
h: R1 = Ph, R2 = COOEt
7a (8%)
+
iso-PrOH, reflux
(For 3a, entry 5 in Table 1)
Ph
6a (10%)
i: R1 = Ph, R2 = 4-ClC6H4
j: R1 = Ph, R2 = 4-MeOC6H4
Scheme 1.
* Corresponding author. Tel.: +82 62 530 3381; fax: +82 62 530 3389.
E-mail address: kimjn@chonnam.ac.kr (J. N. Kim).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.07.141

5864
S. H. Kim et al. / Tetrahedron Letters 49 (2008) 5863–5866
Table 1
Optimization for the synthesis of 7a
Table 2 (continued)
pyridines would provide valuable pyridine derivatives, which
could be used for many purposes.7–9 In this respect, we decided
to examine the feasibility for the regioselective introduction of
acetoxy or alkoxy group at the ortho-position of 2-aryl moiety (vide
infra, Scheme 1).
Entry
Substratea (%)
Ph
Productb (%)
Ph
Ph
Ph
N
HO
7
N
Starting material 3a was prepared as reported in good yield.6
With this compound 3a, we examined acetoxylation as the first
trial under the reported conditions which comprised Pd(OAc)2/
PhI(OAc)2/AcOH/Ac2O at 100–110 °C.4 Compound 4a was synthe-
sized in 61% yield in 1 h (Scheme 1, entry 1 in Table 1). The use
of Oxone (potassium peroxymonosulfate) or the reaction in tert-
BuOH resulted in lower yield of product 4a (entries 2 and 3).
3g (75/85)
7g (28)
O
COOEt
Ph
Ph
O
8
9
N
N
3h (82/73)
7h (80)
Cl
Cl
Ph
Ph
Table 2
N
N
Synthesis of ortho-hydroxyaryl pyridines 7a–j
3i (74/80)
7i (58)
HO
Entry
Substratea (%)
Productb (%)
OMe
OMe
Ph
Ph
Ph
Ph
Ph
Ph
N
HO
1
N
10
N
N
3a (77/88)
7a (76)
3j (73/78)
7j (58)
HO
Ph(4-OMe)
Ph(4-OMe)
a
Prepared according to Ref. 6 and the first yield refer to the first SN20 step and the
second one to the synthesis of pyridine.
Ph
Ph
2
3
4
5
6
N
N
b
Conditions: Substrate 3 (1.0 equiv), Pd(OAc)2 (10 mol %), PEG-3400/t-BuOH,
3b (82/79)
7b (61)
OMe
HO
OMe
Oxone (5.0 equiv), 80–90 °C, 2 h.
c
No reaction even at 120 °C.
Ph
Ph
Ph
Ph
N
N
As a next trial, the synthesis of alkoxy derivatives was examined
under the conditions of Pd(OAc)2/Oxone/alcohol (Scheme 1, entries
4 and 5 in Table 1). The reaction was sluggish and the correspond-
ing methoxy- and iso-propoxy derivatives, 5a and 6a, were ob-
tained in only 10–11% yields. However, we observed the
formation of phenol derivative 7a, albeit in low yields (3–8%), very
interestingly. We thought that the yield of 7a could be increased by
using non-oxidizable alcohol solvent such as tert-butanol instead
of methanol or 2-propanol. Thus, a variety of conditions were
examined in order to find an optimized one (entries 6–10 in Table
1). As expected, 7a was isolated in 64% yield in tert-butanol (entry
6). The use of tert-amyl alcohol or acetonitrile was less effective
(entries 7 and 9). The best yield of 7a was observed when the reac-
tion was carried out in PEG-3400/tert-butanol10 as reaction med-
ium with 5.0 equiv of Oxone (76%, entry 8). The use of K2S2O8
was less effective (entry 10).
3c (79/81)
7c (58)
Cl
HO
Cl
Ph
Ph
Ph
Ph
Ph
Ph
N
N
3d (75/80)
7d (61)
Me
HO
Me
Ph
Ph
N
N
7e (not)c
3e (86/75)
HO
Ph
Ph
Ph
Ph
N
N
7f (not)c
Encouraged by the results, we synthesized various 2-arylpyri-
3f (72/77)
HO
dine derivatives 3b–j according to our previous Letter.6 Introduction

S. H. Kim et al. / Tetrahedron Letters 49 (2008) 5863–5866
5865
2. For the Pd-mediated ortho-arylation of 2-arylpyridine and related compounds,
see: (a) Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2007, 129, 11904–11905; (b)
Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047–14049;
(c) Deprez, N. R.; Kalyani, D.; Krause, A.; Sanford, M. S. J. Am. Chem. Soc. 2006,
128, 4972–4973; (d) Kalyani, D.; Deprez, N. R.; Desai, L. V.; Sanford, M. S. J. Am.
Chem. Soc. 2005, 127, 7330–7331.
Oxone
Ar-OH
7a
[Pd]
3. For the Pd-mediated ortho-halogenation of 2-arylpyridine and related
compounds, see: (a) Kalyani, D.; Dick, A. R.; Anani, W. Q.; Sanford, M. S. Org.
Lett. 2006, 8, 2523–2526; (b) Hull, K. L.; Anani, W. Q.; Sanford, M. S. J. Am. Chem.
Soc. 2006, 128, 7134–7135; (c) Kalyani, D.; Dick, A. R.; Anani, W. Q.; Sanford, M.
S. Tetrahedron 2006, 62, 11483–11498.
O
Ar Pd OH
KO S O Pd OH
O
4. For the Pd-mediated ortho-acetoxylation of 2-arylpyridine and related
compounds, see: (a) Kalyani, D.; Sanford, M. S. Org. Lett. 2005, 7, 4149–4152;
(b) Dick, A. R.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 2300–2301;
(c) Desai, L. V.; Malik, H. A.; Sanford, M. S. Org. Lett. 2006, 8, 1141–1144; (d)
Desai, L. V.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 9542–9543; (e)
Kalberer, E. W.; Whitfield, S. R.; Sanford, M. S. J. Mol. Catal. A 2006, 251,
108–113; (f) Wang, G.-W.; Yuan, T.-T.; Wu, X.-L. J. Org. Chem. 2008, 73, 4717–
4720.
ArH
3a
KHSO4
Scheme 2.
5. For other examples on the transition metal-catalyzed ortho-functionalization of
2-arylpyridine and related compounds, see: (a) Yu, W.-Y.; Sit, W. N.; Lai, K.-M.;
Zhou, Z.; Chan, A. S. C. J. Am. Chem. Soc. 2008, 130, 3304–3306; (b) Dyker, G.
Angew. Chem., Int. Ed. 1999, 38, 1698–1712; (c) Spencer, J.; Chowdhry, B. Z.;
Mallet, A. I.; Rathnam, R. P.; Adatia, T.; Bashall, A.; Rominger, F. Tetrahedron
2008, 64, 6082–6089; (d) Matsuura, Y.; Tamura, M.; Kochi, T.; Sato, M.; Chatani,
N.; Kakiuchi, F. J. Am. Chem. Soc. 2007, 129, 9858–9859; (e) Imoto, S.; Uemura,
T.; Kakiuchi, F.; Chatani, N. Synlett 2007, 170–172; (f) Ozdemir, I.; Demir, S.;
Cetinkaya, B.; Gourlaouen, C.; Maseras, F.; Bruneau, C.; Dixneuf, P. H. J. Am.
Chem. Soc. 2008, 130, 1156–1157; (g) Oi, S.; Sato, H.; Sugawara, S.; Inoue, Y. Org.
Lett. 2008, 10, 1823–1826; (h) Vogler, T.; Studer, A. Org. Lett. 2008, 10, 129–131;
(i) Chen, X.; Hao, X.-S.; Goodhue, C. E.; Yu, J.-Q. J. Am. Chem. Soc. 2006, 128,
6790–6791.
of ketone compound 2 at the primary position of Baylis-Hillman
acetate 1 was carried out with the aid of K2CO3 in DMF in good yields
(72–86%). Next, pyridine synthesis with NH4OAc was also carried
out as reported in 73–88% yields.6 With these starting materials
we examined the selective ortho-hydroxylation under the opti-
mized conditions and the results are summarized in Table 2.
The corresponding 2-hydroxy derivatives were synthesized in
moderate to good yields in most cases (7a–d, 7i, 7j). Tricyclic com-
pound 7h was obtained in good yield (80%) when we used 3h (en-
try 8). This compound must be formed via the intramolecular
lactonization of the initially generated ortho-hydroxy intermedi-
ate. However, the reaction was completely failed with 2,5-di-
methyl and 2,4-dimethyl derivatives, 3e and 3f (entries 5 and 6).
We could not obtain any trace amounts of desired products (7e,
7f) in these cases even at elevated temperature. Whereas we
obtained low yield of product 7g (28%) from 3,4-dimethyl deriva-
tive 3g (entry 7). Based on the experimental results, the failure
for the dimethyl cases, 3e and 3f, might be due to the steric effect
of the ortho-methyl group, which makes the formation of the
palladacycle intermediate difficult.
When we add some water to the reaction mixture of 3a, the
yield of 7a was decreased. When the reaction was carried out un-
der strictly controlled nitrogen atmosphere, compound 7a was ob-
tained in a similar yield. From these experiments, we tentatively
propose the mechanism involving the Oxone as a plausible source
of oxygen atom (Scheme 2): Oxidative insertion of Pd(0) into the
weak O–O bond of Oxone1a and the liberation of product (ArOH)
and KHSO4. Further studies on the reaction mechanism and
the synthetic applicability of these findings are actively under
progress.11–13
6. Kim, S. H.; Kim, K. H.; Kim, H. S.; Kim, J. N. Tetrahedron Lett. 2008, 49, 1948–
1951.
7. For the synthesis and biological activities of 2-(2-hydroxyaryl)pyridine
derivatives, see: (a) Murata, T.; Shimada, M.; Sakakibara, S.; Yoshino, T.;
Masuda, T.; Shintani, T.; Sato, H.; Koriyama, Y.; Fukushima, K.; Nunami, N.;
Yamauchi, M.; Fuchikami, K.; Komura, H.; Watanabe, A.; Ziegelbauer, K. B.;
Bacon, K. B.; Lowinger, T. B. Bioorg. Med. Chem. Lett. 2004, 14, 4019–4022; (b)
Murata, T.; Shimada, M.; Kadono, H.; Sakakibara, S.; Yoshino, T.; Masuda, T.;
Shimazaki, M.; Shintani, T.; Fuchikami, K.; Bacon, K. B.; Ziegelbauer, K. B.;
Lowinger, T. B. Bioorg. Med. Chem. Lett. 2004, 14, 4013–4017; (c) Murata, T.;
Shimada, M.; Sakakibara, S.; Yoshino, T.; Kadono, H.; Masuda, T.; Shimazaki,
M.; Shintani, T.; Fuchikami, K.; Sakai, K.; Inbe, H.; Takeshita, K.; Niki, T.;
Umeda, M.; Bacon, K. B.; Ziegelbauer, K. B.; Lowinger, T. B. Bioorg. Med. Chem.
Lett. 2003, 13, 913–918; (d) Hong, F.; Hollenback, D.; Singer, J. W.; Klein, P.
Bioorg. Med. Chem. Lett. 2005, 15, 4703–4707; (e) Nason, D. M.; Heck, S. D.;
Bodenstein, M. S.; Lowe, J. A., III; Nelson, R. B.; Liston, D. R.; Nolan, C. E.;
Lanyon, L. F.; Ward, K. M.; Volkmann, R. A. Bioorg. Med. Chem. Lett. 2004, 14,
4511–4514; (f) Cheney, I. W.; Yan, S.; Appleby, T.; Walker, H.; Vo, T.; Yao, N.;
Hamatake, R.; Hong, Z.; Wu, J. Z. Bioorg. Med. Chem. Lett. 2007, 17, 1679–
1683.
8. For the applications of 2-(2-hydroxyaryl)pyridine derivatives, see: (a)
Reichardt, C.; Che, D.; Heckenkemper, G.; Schafer, G. Eur. J. Org. Chem. 2001,
2343–2361; (b) Lam, F.; Xu, J. X.; Chan, K. S. J. Org. Chem. 1996, 61, 8414–8418.
9. For our recent reports on the synthesis of pyridine and related compounds
from Baylis-Hillman adducts, see: (a) Gowrisankar, S.; Lee, H. S.; Kim, J. M.;
Kim, J. N. Tetrahedron Lett. 2008, 49, 1670–1673; (b) Lee, M. J.; Kim, S. C.; Kim, J.
N. Bull. Korean Chem. Soc. 2006, 27, 439–442; (c) Park, D. Y.; Lee, M. J.; Kim, T.
H.; Kim, J. N. Tetrahedron Lett. 2005, 46, 8799–8803.
10. The following is typical procedure for the synthesis of 7a: A mixture of 3a
(168 mg, 0.5 mmol), Pd(OAc)2 (11 mg, 0.05 mmol), Oxone (1.54 g, 2.5 mmol) in
PEG-3400 (1.0 g) and tert-butanol (2 mL) was heated to 80–90 °C for 2 h. After
cooling to room temperature, the reaction mixture was poured into water and
extracted with ether. Pure product 7a was obtained by column separation
process (hexanes/CH2Cl2/EtOAc, 20:3:1) as a yellow solid, 134 mg (76%). Other
compounds were synthesized analogously and the selected spectroscopic data
of 7a, 7c, 7d, 7h, 4a and 5a are as follows.
In summary, we disclosed the synthesis of poly-substituted pyr-
idines functionalized with hydroxyl group regioselectively via the
Pd-mediated C–H activation process. Further studies on the reac-
tion mechanism and the biological activities of prepared com-
pounds are currently underway.
Compound 7a: 76%; Yellow solid, mp 146–147 °C; IR (KBr) 3446, 1601, 1450,
1439 cmꢀ1 1H NMR (CDCl3, 300 MHz) d 2.56 (s, 3H), 4.05 (s, 2H), 6.39–6.45 (m,
;
1H), 6.81 (dd, J = 8.1 and 1.5 Hz, 1H), 6.99 (dd, J = 8.1 and 1.5 Hz, 1H), 7.08–7.36
(m, 11H), 7.48 (s, 1H), 13.18 (br s, 1H); 13C NMR (CDCl3, 75 MHz) d 21.82, 38.21,
117.82, 117.86, 120.24, 126.55, 127.41, 128.62, 128.71, 128.73, 129.17, 130.06,
131.21, 132.44, 133.93, 138.58, 140.21, 142.14, 152.34, 153.21, 158.39; ESIMS
m/z 352 (M++1). Anal. Calcd for C25H21NO: C, 85.44; H, 6.02; N, 3.99. Found: C,
85.21; H, 6.34; N, 3.87.
Acknowledgements
This study was financially supported by Chonnam National
University, 2007. Spectroscopic data were obtained from the Korea
Basic Science Institute, Gwangju branch.
Compound 7c: 58%; White solid, mp 137–138 °C; IR (KBr) 3419, 1602, 1568,
1424, 1086 cmꢀ1 1H NMR (CDCl3, 300 MHz) d 2.55 (s, 3H), 4.04 (s, 2H), 6.38
;
(dd, J = 8.4 and 2.1 Hz, 1H), 6.72 (d, J = 8.4 Hz, 1H), 6.99 (d, J = 2.1 Hz, 1H), 7.14–
7.39 (m, 10H), 7.47 (s, 1H), 13.76 (br s, 1H); 13C NMR (CDCl3, 75 MHz) d 21.77,
38.21, 117.99, 118.09, 118.57, 126.63, 127.66, 128.62, 128.76, 128.94, 129.09,
131.90, 132.77, 133.96, 135.14, 138.42, 139.84, 142.26, 151.45, 153.19, 159.62;
ESIMS m/z 386 (M++1). Anal. Calcd for C25H20ClNO: C, 77.81; H, 5.22; N, 3.63.
Found: C, 78.03; H, 5.47; N, 3.60.
References and notes
1. For the Pd-mediated ortho-alkylation of 2-arylpyridine and related compounds,
see: (a) Zhang, Y.; Feng, J.; Li, C.-J. J. Am. Chem. Soc. 2008, 130, 2900–2901; (b)
Chen, X.; Li, J.-J.; Hao, X.-S.; Goodhue, C. E.; Yu, J.-Q. J. Am. Chem. Soc. 2006, 128,
78–79; (c) Chen, X.; Goodhue, C. E.; Yu, J.-Q. J. Am. Chem. Soc. 2006, 128, 12634–
12635.
Compound 7d: 61%; Pale yellow solid, mp 133–134 °C; IR (KBr) 3419, 1626,
1450, 1426 cmꢀ1 1H NMR (CDCl3, 500 MHz) d 2.23 (s, 3H), 2.54 (s, 3H), 4.03 (s,
;

5866
S. H. Kim et al. / Tetrahedron Letters 49 (2008) 5863–5866
2H), 6.24 (dd, J = 8.0 and 1.5 Hz, 1H), 6.69 (d, J = 8.0 Hz, 1H), 6.81 (d, J = 1.0 Hz,
1H), 7.15 (d, J = 7.5 Hz, 2H), 7.21–7.35 (m, 8H), 7.45 (s, 1H), 13.35 (br s, 1H); 13
Compound 5a: 11%; Pale yellow oil; IR (film) 1600, 1493, 1426, 1246 cmꢀ1
NMR (CDCl3, 300 MHz) d 2.59 (s, 3 H), 3.23 (s, 3H), 4.06 (s, 2H), 6.63 (dd, J = 8.4
;
1H
C
NMR (CDCl3, 125 MHz) d 21.29, 21.80, 38.19, 117.41, 118.24, 118.89, 126.52,
127.34, 128.62, 128.70, 128.74, 129.15, 130.94, 131.95, 133.58, 138.68, 140.44,
140.50, 142.12, 152.50, 153.02, 158.47; ESIMS m/z 366 (M++1). Anal. Calcd for
and 0.9 Hz, 1H), 6.99 (td, J = 7.5 and 0.9 Hz, 1H), 7.06–7.10 (m, 2H), 7.13–7.17
(m, 3H), 7.21–7.27 (m, 4H), 7.29–7.34 (m, 2H), 7.40 (s, 1H), 7.44 (dd, J = 7.2 and
1.2 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 22.41, 38.57, 54.72, 110.77, 120.80,
126.35, 126.54, 127.58, 128.57, 128.61, 128.91, 129.32, 129.87, 131.45, 132.74,
135.07, 138.42, 139.15, 140.32, 152.43, 155.59, 156.15; ESIMS m/z 366 (M++1).
11. The use of Pd(PPh3)4 instead of Pd(OAc)2 caused less reactivity in the reaction
of 3a, as an example. The use of H2O2 (30% solution) instead of Oxone produced
7a in trace amounts (<10%).
12. The reaction of acetophenone oxime methyl ether afforded the corresponding
2-hydroxy product in 47%.4c Whereas the reaction of 2-phenylpyridine gave 2-
hydroxy compound in only 5% (2-phenylpyridine was recovered in 16% and
dimeric compound2b was isolated in 20%).
13. Recently, Cu(II)-catalyzed ortho-hydroxylation of 2-phenylpyridine has been
reported using O2 as an oxidant and they used water as an anion (OH) source in
the reaction.5i Sanford and coworkers also observed Pd(OAc)2-catalyzed C–H
bond methoxylation with MeOH/Oxone and they proposed the mechanism
involving PdIV intermediate.4c
C26H23NO: C, 85.45; H, 6.34; N, 3.83. Found: C, 85.37; H, 6.59; N, 3.98.
Compound 7h: 80%; White solid, mp 186–187 °C; IR (KBr) 1722, 1608, 1173,
1112 cmꢀ1 1H NMR (CDCl3, 300 MHz) d 2.68 (s, 3H), 4.12 (s, 2H), 7.13–7.16 (m,
;
2H), 7.22–7.57 (m, 6H), 8.27 (s, 1H), 8.57–8.60 (m, 1H); 13C NMR (CDCl3,
75 MHz) d 23.78, 38.80, 115.29, 117.05, 119.37, 124.51, 124.68, 126.81, 128.70,
128.84, 131.60, 135.48, 137.86, 137.99, 149.44, 152.50, 161.51, 165.37; ESIMS
m/z 302 (M++1). Anal. Calcd for C20H15NO2: C, 79.72; H, 5.02; N, 4.65. Found: C,
00.00; H, 0.00; N, 0.00.
Compound 4a: 61%; Pale yellow solid, mp 121–122 °C; IR (KBr) 1764, 1428,
1212, 1191 cmꢀ1
;
1H NMR (CDCl3, 300 MHz) d 2.00 (s, 3H), 2.56 (s, 3H), 4.07 (s,
2H), 7.05–7.35 (m, 14H), 7.45 (s, 1H); 13C NMR (CDCl3, 75 MHz) d 20.88, 22.23,
38.48, 122.67, 125.43, 126.41, 127.07, 128.07, 128.63, 128.71, 128.77, 129.06,
132.03, 132.75, 133.11, 134.43, 138.93, 139.14, 139.19, 148.29, 151.04, 155.51,
168.53; ESIMS m/z 394 (M++1).