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Article

Palladium(II)-Catalyzed othro-C–H-Benzoxylation of 2-Arylpyridines by Oxidative Coupling with Aryl Acylperoxides

by
Wing-Nga Sit
,
Chun-Wo Chan
and
Wing-Yiu Yu
*
State Key Laboratory of Chirosciences and Department of Applied Biology and Chemical Technology, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
*
Author to whom correspondence should be addressed.
Molecules 2013, 18(4), 4403-4418; https://doi.org/10.3390/molecules18044403
Submission received: 5 March 2013 / Revised: 21 March 2013 / Accepted: 21 March 2013 / Published: 15 April 2013
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Versions Notes

Abstract

:
A palladium(II)-catalyzed ortho-benzoxylation of 2-arylpyridines with aryl acylperoxides was developed. With pyridyl as directing group, the benzoxylation reaction exhibits remarkable regioselectivity and excellent functional group tolerance, providing the products in up to 87% yield.

1. Introduction

Site selective direct functionalization of C–H bonds is attracting considerable current attention for developing sustainable chemical synthesis. Without relying on prefunctionalized substrates, the direct C–H functionalization approach would streamline the synthetic routes and improve atom economy. With transition metal catalysis, innovative transformations based on regioselective aryl C–H bond cleavage with the formation of C–C and C–X (X = halogen) bonds have been achieved [1,2,3]. Recently, significant advances have been made in the analogous transformations with C–O bond formation on arenes. For instance, the research groups of Sanford, Crabtree and Wang achieved acetoxylation of aryl C–H bonds with oxidants such as Oxone®, PhI(OAc)2, and K2S2O8 [4,5,6]. The analogous acetoxylation of selected sp3 C–H bonds has also been achieved independently by Sanford, Yu and Corey [7,8,9]. Notably, Yu and co-workers accomplished Pd-catalyzed arene hydroxylation with dioxygen as oxidant [10]. Apart from Pd, Cu(OAc)2 has also been shown to exhibit promising reactivities toward catalytic acetoxylation of aryl C–H bonds [11].
Compared to acetoxylation, the analogous benzoxylation is less developed [12]. Aryl benzoates are known to form structures of some natural products such as the gilvocarcins (Figure 1) [13,14]. In 2009, Cheng and co-workers reported the Rh(I)-catalyzed ortho-benzoxylation of 2-arylpyridines with benzoic acids [15]. Later, the same group also reported the analogous Cu(OAc)2-catalyzed benzoxylations with benzoic anhydride and derivatives [16,17]. With a continuing interest in developing catalytic C–H bond cross coupling reactions, we have been investigating the regioselective C–C and C–N bond cross coupling reactions based on the coupling reactions of arylpalladium and –rhodium complexes with carboradicals [18,19,20,21], carbenes [22] and nitrenoids [23,24,25]. Previously, we described the successful development of the Pd-catalyzed decarboxylative arylation of 2-arylpyridines with aryl acylperoxides [19]. Prompted by this work, here we disclose the Pd-catalyzed regioselective benzoxylation of 2-arylpyridines with aryl acylperoxides.
Molecules 18 04403 g001 550
Figure 1. Examples of gilvocarins.
Figure 1. Examples of gilvocarins.
Molecules 18 04403 g001

2. Results and Discussion

In our earlier study on decarboxylative arylation, we found that treating 2-phenylpyridine (1a, 0.25 mmol) with Pd(OAc)2 (5 mol%) with a methoxy-substituted aryl acylperoxide (4 × 0.5 equiv./0.5 h) at 100 °C for 2 h in CH3CN (Scheme 1) furnished 2k in 90% isolated yield. However, when simple benzoyl peroxide was employed as reagent, the analogous reaction of 1a produced 2a in only 7% yield. To develop a general benzoxylation reaction, we first examined the solvent effect (Table 1). With 1a as substrate and benzoyl peroxide as reagent (4 × 0.5 equiv./0.5 h), the best result (2a: 49%) was obtained when xylene was employed as solvent (entry 8). As expected, toluene gave comparable results; the use of other donor solvents (e.g., dioxane, THF, DMF and DCE) produced far inferior outcomes.
Molecules 18 04403 g002 550
Scheme 1. Initial studies of othro-C-H-arylcarboxylation by aryl acylperoxide.
Scheme 1. Initial studies of othro-C-H-arylcarboxylation by aryl acylperoxide.
Molecules 18 04403 g002
We next turned to optimize other experimental parameters, and the results are summarized in Table 2. We found that when raising the reaction temperature to 120 °C led to slightly lower yield of 41% for the benzoxylation of 1a (entry 2). Notably, further increasing the temperature to 130 °C afforded 2a in 59% yield (entry 3). Either prolonged reaction time or higher temperature (150 °C) did not give better results (entries 4–5). After several trials, we found that employing 3.5 equiv. of benzoyl peroxide added in a batchwise fashion (7 × 0.5 equiv./0.5 h) improved the benzoxylation yield to 64% (entry 6). Interestingly, when dried benzoyl peroxide was employed, 2a was obtained in 70% yield. Up to 76% yield of 2a was obtained when 10 mol% of Pd(OAc)2 was employed for the benzoxylation reaction (entry 9).
Table
Table 1. Solvent effect. Molecules 18 04403 i002
Table 1. Solvent effect. Molecules 18 04403 i002
EntrySolvent (2 mL)GC Yield (%)
1CH3CN7
2dioxane10
3THF29
4DMF33
5DMA3
6DCE11
7toluene47
8xylene49
Table
Table 2. Effect of other experimental parameters. Molecules 18 04403 i003
Table 2. Effect of other experimental parameters. Molecules 18 04403 i003
EntryAddition methodTemp. (°C)Time (h)GC Yield (%)
14 × 0.5 equiv./0.5 h100249
24 × 0.5 equiv./0.5 h120241
34 × 0.5 equiv./0.5 h130259
44 × 0.5 equiv./1 h130453
54 × 0.5 equiv./0.5 h150252
67 × 0.5 equiv./0.5 h1303.564
78 × 0.5 equiv./0.5 h130460
8 *7 × 0.5 equiv./0.5 h1303.570
9 *,#7 × 0.5 equiv./0.5 h1303.576
* Peroxide was washed with diethyl ether and air dry; # 10 mol% of Pd(OAc)2 was used.
Table 3 depicts the substrate scope study, and the Pd-catalyzed benzoxylation is broadly applicable to a variety of 2-arylpyridines. In all cases, benzoxylation occurs at the ortho-C-H bond to the pyridyl group. For meta-substituted arenes (e.g., 1d and 1e), benzoxylation occurred regioselectively at the less hindered ortho-C-H bond (entries 4–7). Apparently, those aryl groups bearing electron-donating substituent such as Me, MeO produced better yields of 2d and 2e (83%–87%), whereas the analogous reactions of substrates with electron-withdrawing CF3 and F groups resulted in 54%–62% yields. Higher benzoxylation yield was also observed with 1h, which contains a Me group on the pyridyl function. Presumably, stronger coordination of the pyridyl group would facilitate cyclopalladation, thereby speeding up the substrate conversion. Consistent with this notion is that benzoxylation of benzoquinoline 1j was equally facile with 2j being obtained in 85% yield. The rigid scaffold of 1j should lower the entropic cost for the cyclopalladation (entry 10). The molecular structure of 2i has been established by X-ray crystallography. CCDC 933423 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; e-mail: [email protected]), see Supporting Information.
Table
Table 3. Pd-catalyzed benzoxylation of arylpyridines a.
Table 3. Pd-catalyzed benzoxylation of arylpyridines a.
EntrySubstrateProductIsolated Yield (%)
1 Molecules 18 04403 i0041a Molecules 18 04403 i0052a71
2 Molecules 18 04403 i0061b Molecules 18 04403 i0072b70
3 Molecules 18 04403 i0081c Molecules 18 04403 i0092c44
4 Molecules 18 04403 i0101d Molecules 18 04403 i0112d87
5 Molecules 18 04403 i0121e Molecules 18 04403 i0132e83
6 Molecules 18 04403 i0141f Molecules 18 04403 i0152f54
7 Molecules 18 04403 i0161g Molecules 18 04403 i0172g62
8 Molecules 18 04403 i0181h Molecules 18 04403 i0192h87
9 Molecules 18 04403 i0201i Molecules 18 04403 i0212i57
10 Molecules 18 04403 i0221j Molecules 18 04403 i0232j85
a Reaction conditions: substrate (0.5 mmol), Pd(OAc)2 (5 mol%), peroxide (7 × 0.5 equiv./0.5 h), at 130 °C for 3.5 h in xylene (2 mL).
Table 4 depicts the scope of the aryl acylperoxides; the Pd-catalyzed benzoxylations of 1a afforded the corresponding benzoates in 27%–81% yields. Peroxides with electron-donating (e.g., Me, MeO, EtO) and -withdrawing (e.g., CF3) are effective reagents for the benzoxylation. Peroxides with bulky substituents such as tBu and naphthalene were also tolerated with benzoates being formed in 44%–77% yields.
Table
Table 4. Benzoxylation with various aryl acylperoxides a. Molecules 18 04403 i024
Table 4. Benzoxylation with various aryl acylperoxides a. Molecules 18 04403 i024
EntryArIsolated Yield (%)
14-OMe-C6H554
23-OMe-C6H569
32-Cl-C6H543
43-Cl-C6H573
52-Me-C6H566
64-Me-C6H564
74-F-C6H555
84-Br-C6H530
94-CF3-C6H581
104-OEt-C6H527
114-tBu-C6H577
122,6-F2-C6H446
132-naphthalene44
a Reaction conditions: substrate (0.5 mmol), Pd(OAc)2 (5 mol% ), peroxide (7 × 0.5 equiv./0.5 h), at 130 °C for 3.5 h in xylene (2 mL).
A plausible mechanism is shown in Scheme 2. The benzoxylation is probably initiated by the pyridyl-assisted cyclopalladation of the ortho-C-H of the arenes. Our earlier study showed that the regioselectivity of the cyclopalladation is determined by steric factor [19]. Substrates with a meta-substituted group would be palladated at the least hindered site. Regarding to the nature of the palladation step, our previous studies established a linear free energy relationship (ρ+ = −0.74) for the Pd-catalyzed oxidative acylation of pivilanilides, consistent with an electrophilic mechanism [21]. We conjectured that homolytic O–O cleavage of the aryl acylperoxide should afford arylcarboxy radicals [26], which would react with the palladacyclic intermediate leading to the C–O bond formation.

3. Experimental

3.1. General

2-Arylpyridines were prepared by reacting the corresponding arylboronic acids with 2-bromopyridines using reported procedures [27]. Aryl acylperoxides were prepared by reacting acid chlorides with hydrogen peroxide (35 wt. % in H2O) and sodium hydroxide by the reported procedures [28]. Benzoyl peroxide (Luperox® A75) was obtained commercially and washed with diethyl ether and air dry. Thin layer chromatography was performed on silica gel plates. Silica gel (Merck, 230–400 mesh) and aluminum oxide (Merck, 50–200 mesh) were used for flash column chromatography. 1H 400 MHz) and 13C-NMR spectra (100 MHz) were recorded on a Brüker DPX 400 NMR spectrometer, chemical shift (δ) valued are given in ppm and are referenced to the residual solvent peaks. Coupling constants (J) were reported in Hertz (Hz). Mass spectra and high resolution mass spectra (HRMS) were obtained on a VG Micromass Fison VG platform, a Finnigan Model Mat 95 ST instrument, or a Brüker APEX 47e FT-ICR mass spectrometer. Infrared analysis were measured on a Nicolet Magna 750 FTIR spectrometer. Melting points were measured on a Büchi B-545 melting point apparatus. The X-ray crystal structure was obtained on a Brüker CCD area detector diffractometer.
Molecules 18 04403 g003 550
Scheme 2. Plausible mechanism of othro-C-H-benzoxylation by aryl acylperoxides.
Scheme 2. Plausible mechanism of othro-C-H-benzoxylation by aryl acylperoxides.
Molecules 18 04403 g003

3.2. General Procedure for the Pd-Catalyzed Benzoxylation

A mixture of substrate (0.5 mmol), Pd(OAc)2 (0.025 mmol, 5 mol%), aryl acylperoxide [1.75 mmol; addition interval: 7 × 0.5 equiv./0.5 h] in xylene (2 mL) was sealed in a 8-mL vial with a Teflon-lined cap. The mixture was heated at 130 °C (oil bath temperature) for 3.5 h. After cooling down to room temperature, the reaction mixture was filtered through a plug of silica gel, and the filtrate was concentrated under vacuum to afford an oily substance. The crude product was dissolved in dichloromethane and treated with saturated aqueous NaHCO3 (3 × 10 mL) solution and extracted with dichloromethane (4 × 10 mL). The combined organic extracts were dried over Na2SO4 and evaporated to dryness by a rotary evaporator. The residue was loaded to a silica gel column for purification by flash chromatography using 60% n-hexane/40% diethyl ether as eluent.

3.3. Characterization of Products

2-(Pyridin-2-yl)phenyl benzoate (2a). Yellow oil (71% yield). 1H-NMR (CDCl3): δH 8.59 (d, J = 4.7 Hz, 1H), 8.09 (d, J = 7.8 Hz, 2H), 7.78 (d, J = 7.6 Hz, 1H), 7.55–7.63 (m, 3H), 7.38–7.52 (m, 4H), 7.31 (d, J = 8.0 Hz, 1H), 7.13–7.16 (m, 1H). 13C-NMR (CDCl3): δC 165.2 (C=O), 154.7(C), 150.2 (C-O), 149.4 (C-H), 136.7 (C-H), 134.0 (C-H), 131.5 (C-H), 130.7 (C-H), 130.3 (C), 129.1 (C), 128.9 (C-H), 128.4 (C-H), 127.0 (C-H), 124.2 (C-H), 123.9 (C-H), 122.7 (C-H). MS (EI): 275 (M+, 20), 105 (100), 77 (40). HRMS (ESI): calcd. for C14H13NO2H+: 276.1025, found: 276.1023. IR (KBr, cm−1): 1739.
Molecules 18 04403 i025
5-Methyl-2-(pyridin-2-yl)phenyl benzoate (2b). Yellow oil (70% yield). 1H-NMR (CDCl3): δH 8.57 (d, J = 4.4 Hz, 1H), 8.10 (d, J = 7.5 Hz, 2H), 7.69 (d, J = 7.9 Hz, 1H), 7.50–7.61 (m, 3H), 7.45 (t, J = 7.7 Hz, 2H), 7.21 (d, J = 8.3 Hz, 1H), 6.93–6.97 (m, 1H), 2.43 (s, 3H). 13C-NMR (CDCl3): δC 165.9 (C=O), 156.2 (C), 150.1 (C-O), 149.4 (C-H), 140.8 (C), 136.7 (C-H), 134.0 (C), 131.3 (C-H), 131.0 (C-H), 130.6 (C-H), 130.2 (C), 129.1 (C-H), 128.4 (C-H), 124.2 (C), 122.5 (C-H), 122.1 (C-H), 21.9 (CH3). MS (EI): 289 (M+, 40), 105 (100), 77 (40). HRMS (ESI): calcd. for C19H15NO2H+: 290.1181, found: 290.1188. IR (KBr, cm−1): 1736.
Molecules 18 04403 i026
5-Formyl-2-(pyridin-2-yl)phenyl benzoate (2c). Yellow oil (44% yield based on conversion). 1H-NMR (CDCl3): δH 10.07 (s, 1H), 8.62 (d, J = 4.6 Hz, 1H), 8.08 (d, J = 7.3 Hz, 2H), 7.95–8.00 (m, 2H), 7.91 (dd, J = 7.9, 1.2 Hz, 1H), 7.83 (d, J = 1.2 Hz, 1H), 7.60–7.67 (m, 2H), 7.48 (d, J = 8.2 Hz, 1H), 7.21–7.23 (m, 1H). 13C-NMR (CDCl3): δC 191.5 (C=O), 165.5 (C=O), 154.9 (C), 150.5 (C-O), 146.7 (C-H), 139.6 (C-H), 137.0 (C-H), 134.5 (C), 132.5 (C-H), 130.9 (C), 129.6 (C-H), 127.4 (C-H), 126.6 (C-H), 125.2 (C-H), 123.6 (C-H), 120.7 (C-H). MS (EI): 303 (M+, 10), 105 (100), 77 (30). HRMS (ESI): calcd. for C19H13NO3H+: 304.0974, found: 304.0981. IR (KBr, cm−1): 1738, 1697.
Molecules 18 04403 i027
4-Methyl-2-(pyridin-2-yl)phenyl benzoate (2d). Yellow oil (87% yield). 1H-NMR (CDCl3): δH 8.61 (d, J = 4.7 Hz, 1H), 8.09 (d, J = 7.4 Hz, 2H), 7.55–7.61 (m, 4H), 7.44 (t, J = 7.7 Hz, 2H), 7.28 (dd, J = 9.0, 2.1 Hz, 1H), 7.19 (d, J = 8.2 Hz, 1H), 7.12–7.15 (m, 1H), 2.44(s, 3H). 13C-NMR (CDCl3): δC 165.9 (C=O), 156.2 (C), 150.2 (C-H), 146.6 (C), 136.7 (C-H), 134.0 (C), 133.4 (C-H), 131.9 (C-H), 130.9 (C), 130.7 (C-H), 130.1 (C-H), 129.1 (C-H), 128.4 (C-H), 124.3 (C-H), 123.6 (C-H), 122.2 (C-H), 21.5 (CH3). MS (EI): 289 (M+, 30), 105 (100), 77 (30). HRMS (ESI): calcd. for C19H15NO2H+: 290.1181, found: 290.1184. IR (KBr, cm−1): 1738.
Molecules 18 04403 i028
4-Methoxy-2-(pyridin-2-yl)phenyl benzoate (2e). Yellow oil (83% yield). 1H-NMR (CDCl3): δH 8.61 (d, J = 4.7 Hz, 1H), 8.09 (d, J = 7.4 Hz, 2H), 7.57–7.62 (m, 2H), 7.45 (t, J = 7.7 Hz, 2H), 7.34 (d, J = 3.0 Hz, 1H), 7.22 (d, J = 8.8 Hz, 1H), 7.13–7.17 (m, 2H), 7.02 (dd, J = 8.8, 3.0 Hz, 1H), 3.88 (s, 3H). 13C-NMR (CDCl3): δC 166.1 (C=O), 158.2 (C-O), 156.0 (C), 150.2 (C-H), 149.2 (C-O), 142.4 (C-H), 136.8 (C-H), 134.6 (C-H), 134.0 (C), 131.5 (C-H), 129.1 (C-H), 126.4 (C), 124.8 (C-H), 124.3 (C-H), 116.3 (C-H), 115.8 (C-H), 56.3 (CH3). MS (EI): 305 (M+, 40), 105 (100), 77 (30). HRMS (ESI): calcd. for C19H15NO3H+: 306.1130, found: 306.1133. IR (KBr, cm−1): 1737.
Molecules 18 04403 i029
4-Methoxy-2-(pyridin-2-yl)phenyl benzoate (2f). Yellow oil (54% yield). 1H-NMR (CDCl3): δH 8.63 (d, J = 4.5 Hz, 1H), 8.03–8.11 (m, 2H), 7.74 (dd, J = 8.5, 1.6 Hz, 1H), 7.57–7.69 (m, 4H), 7.42–7.50 (m, 3H), 7.22 (d, J = 5.3 Hz, 1H). 13C-NMR (CDCl3): δC 165.3 (C=O), 154.7 (C), 151.5 (C-O), 150.5 (C-H), 137.1 (C-H), 134.6 (C-H), 134.3 (C-H), 130.9 (C-H), 130.7 (C), 129.5 (C-H), 129.3 (C), 129.1 (C-H), 127.3 (C-H), 124.8 (C-H), 124.4 (CF3), 123.7 (C-H), 123.5 (C-H). MS (EI): 343 (M+, 20), 105 (100), 77 (40). HRMS (ESI): calcd. for C19H12NO2F3H+: 344.0898 found: 344.0905. IR (KBr, cm−1): 1739.
Molecules 18 04403 i030
4-Fluoro-2-(pyridin-2-yl)phenyl benzoate (2g). Yellow oil (62% yield). 1H-NMR (CDCl3): δH 8.60 (d, J = 4.7 Hz, 1H), (d, J = 4.7 Hz, 1H), 8.08 (d, J = 7.4 Hz, 2H), 7.52–7.64 (m, 4H), 7.46 (t, J = 7.7 Hz, 2H), 7.25–7.28 (m, 1H), 7.13–7.18 (m, 2H). 13C-NMR (CDCl3): δC 165.8 (C=O), 159.8 (C-F), 154.9 (C), 150.4 (C-H), 144.7 (C-O), 136.9 (C-H), 135.4 (C-H), 134.2 (C-H), 130.8 (C-H), 129.8 (C), 129.2 (C-H), 125.5 (C), 124.2 (C-H), 123.2 (C-H), 117.9 (C-H), 117.1 (C-H). MS (EI): 293 (M+, 20), 105 (100), 77 (40). HRMS (ESI): calcd. for C18H12NO2FH+: 294.0930, found: 294.0927. IR (KBr, cm−1): 1741.
Molecules 18 04403 i031
2-(3-Methylpyridin-2-yl)phenyl benzoate (2h). Yellow oil (87% yield). 1H-NMR (CDCl3): δH 8.42 (d, J = 4.5 Hz, 1H), 7.89 (d, J = 7.5 Hz, 1H), 7.26–7.54 (m, 8H), 7.04–7.07 (m, 1H), 2.21 (s, 3H). 13C-NMR (CDCl3): δC 165.0 (C=O), 155.9 (C), 148.8 (C-O), 147.1 (C-H), 138.3 (C-H), 134.0 (C-H), 133.8 (C-H), 132.6 (C), 130.9 (C-H), 130.6 (C), 130.1 (C-H), 129.7 (C), 128.8 (C-H), 126.4 (C-H), 123.3 (C-H), 123.0 (C-H), 19.5 (CH3). MS (EI): 289 (M+, 30), 105 (100), 77 (40). HRMS (ESI): calcd. for C19H15NO2H+: 290.1181, found: 290.1176. IR (KBr, cm−1): 1736.
Molecules 18 04403 i032
1-(Pyridin-2-yl)naphthalen-2-yl benzoate (2i). Yellow oil (57% yield). 1H-NMR (CDCl3): δH 8.77 (d, J = 4.2 Hz, 1H), 7.93–8.01 (m, 4H), 7.71 (t, J = 7.6 Hz, 1H), 7.63 (d, J = 8.2 Hz, 1H), 7.55–7.57 (m, 1H), 7.44–7.54 (m, 4H), 7.40 (t, J = 7.6 Hz, 2H), 7.24–7.27 (m, 1H). 13C-NMR (CDCl3): δC 165.9 (C=O), 155.4 (C), 150.3 (C-O), 146.7 (C-H), 136.7 (C-H), 134.0 (C-H), 133.4 (C), 132.5 (C-H), 130.6 (C-H), 130.1 (C), 129.8 (C), 129.0 (C-H), 128.8 (C-H), 128.7 (C), 127.7 (C-H), 127.5 (C-H), 126.4 (C-H), 126.2 (C-H), 123.0 (C-H), 122.3 (C-H). MS (EI): 325 (M+, 50), 191 (10) 105 (100), 77 (40). HRMS (ESI): calcd. for C22H15NO2H+: 326.1130, found: 326.1129. IR (KBr, cm−1): 1735.
Molecules 18 04403 i033
Benzo[h]quinolin-10-yl benzoate (2j). Yellow oil (85% yield). 1H-NMR (CDCl3): δH 8.39–8.42 (m, 3H), 8.08 (dd, J = 8.0, 1.8 Hz, 1H), 7.83–7.89 (m, 2H), 7.66–7.75 (m, 3H), 7.53–7.62 (m, 3H), 7.33 (q, J = 4.1 Hz, 1H). 13C-NMR (CDCl3): δC 167.5 (C=O), 149.7 (C-O), 148.5 (C-H), 146.1 (C), 136.6 (C-H), 136.1 (C), 133.3 (C-H), 132.0 (C), 131.1 (C-H), 129.0 (C-H), 128.7 (C), 128.5 (C-H), 127.6 (C-H), 127.3 (C-H), 127.0 (C-H), 124.0 (C), 123.0 (C-H), 122.1 (C-H). MS (EI): 299 (M+, 40), 105 (100), 77 (30). HRMS (ESI): calcd. for C20H13NO2H+: 300.1025, found: 300.1024. IR (KBr, cm−1): 1735.
Molecules 18 04403 i034
2-(Pyridin-2-yl)phenyl 4-methoxybenzoate (2k). Yellow oil (54% yield). 1H-NMR (CDCl3): δH 8.59 (d, J = 4.5 Hz, 1H), 8.03 (d, J = 8.8 Hz, 2H), 7.78 (dd, J = 7.6, 1.5 Hz, 1H), 7.54–7.63 (m, 2H), 7.45 (dt, J = 7.6, 1.5 Hz, 1H), 7.36 (dt, J = 7.5, 0.8 Hz, 1H), 7.29 (dd, J = 7.9, 0.7 Hz, 1H), 7.11–7.14 (m, 1H), 6.91 (d, J = 8.8 Hz, 2H), 3.82 (s, 3H). 13C-NMR (CDCl3): δC 165.4 (C=O), 164.3 (C), 156.1 (C), 150.1 (C), 148.9 (C-H), 136.6 (C-H), 133.9 (C-H), 132.8 (C-H), 131.4 (C-H), 130.2 (C), 126.8 (C-H), 123.9 (C-H), 122.6 (C), 122.2 (C-H), 119.2 (C-H), 114.3 (C-H), 56.0 (CH3). MS (EI): 305 (M+, 20), 135 (100). HRMS (ESI): calcd. for C19H15NO3H+: 306.1130, found: 306.1136. IR (KBr, cm−1): 1732.
Molecules 18 04403 i035
2-(Pyridin-2-yl)phenyl 3-methoxybenzoate (2l). Yellow oil (69% yield). 1H-NMR (CDCl3): δH 8.60 (d, J = 4.1 Hz, 1H), 7.78 (dd J = 7.7, 1.5 Hz, 1H), 7.69 (d, J = 6.6 Hz, 1H), 7.55–7.64 (m, 3H), 7.47 (dt J = 7.7, 1.6 Hz, 1H), 7.35–7.41 (m, 2H), 7.32 (dt J = 8.0, 1.0 Hz, 1H), 7.10–7.17 (m, 2H), 3.81 (s, 3H). 13C-NMR (CDCl3): δC 165.6 (C=O), 160.2 (C), 156.1 (C), 150.2 (C), 148.9 (C-H), 136.8 (C-H), 133.9 (C-H), 131.5 (C), 131.3 (C-H), 130.3 (C-H), 130.1 (C), 127.0 (C-H), 124.3 (C-H), 123.9 (C-H), 123.2 (C-H), 122.8 (C-H), 120.7 (C-H), 115.0 (C-H), 56.0 (CH3). MS (EI): 305 (M+, 20), 135 (100). HRMS (ESI): calcd. for C19H15NO3H+: 306.1130, found: 306.1134. IR (KBr, cm−1): 1736.
Molecules 18 04403 i036
2-(Pyridin-2-yl)phenyl 2-chlorobenzoate (2m). Yellow oil (43% yield). 1H-NMR (CDCl3): δH 8.63 (d, J = 4.7 Hz, 1H), 7.88 (dd, J = 7.8, 1.2 Hz, 1H), 7.74 (dd, J = 7.7, 1.5 Hz, 1H), 7.68 (dt, J = 7.7, 1.7 Hz, 1H), 7.57 (d, J = 7.8 Hz, 1H), 7.37–7.52 (m, 4H), 7.31–7.34 (m, 2H), 7.18–7.21 (m, 1H). 13C-NMR (CDCl3): δC 165.2 (C=O), 156.4 (C), 150.2 (C-O), 148.7 (C-H), 137.0 (C-H), 135.0 (C-Cl), 134.0 (C-H), 133.6 (C-H), 132.5 (C-H), 131.8 (C-H), 131.5 (C), 130.5 (C-H), 130.0 (C), 127.2 (C-H), 124.4 (C-H), 124.0 (C-H), 122.9 (C-H), 122.1 (C-H). MS (EI): 309 (M+, 40), 139 (100), 111 (20). HRMS (ESI): calcd. for C18H12NO2ClH+: 310.0635, found: 310.0628. IR (KBr, cm−1): 1742.
Molecules 18 04403 i037
2-(Pyridin-2-yl)phenyl 3-chlorobenzoate (2n). Yellow oil (73% yield). 1H-NMR (CDCl3): δH 8.57 (d, J = 4.6 Hz, 1H), 8.06 (s, 1H), 7.95 (d, J = 7.8 Hz, 1H), 7.75 (dd, J = 7.7, 1.3 Hz, 1H), 7.65 (t, J = 7.8 Hz, 1H), 7.53–7.57 (m, 2H), 7.48 (t, J = 7.7 Hz, 1H), 7.37–7.42 (m, 2H), 7.30 (d, J = 4.5 Hz, 1H), 7.14–7.18 (m, 1H). 13C-NMR (CDCl3): δC 164.6 (C=O), 156.1 (C), 150.2 (C-O), 148.7 (C-H), 136.9 (C-H), 135.2 (C-Cl), 134.0 (C-H), 133.8 (C), 131.9 (C-H), 131.5 (C-H), 130.7 (C-H), 130.4 (C-H), 129.9 (C), 128.8 (C-H), 127.2 (C-H), 124.2 (C-H), 123.8 (C-H), 122.8 (C-H). MS (EI): 309 (M+, 20), 139 (100), 111 (40). HRMS (ESI): calcd. for C18H12NO2ClH+: 310.0635, found: 310.0640. IR (KBr, cm−1): 1740.
Molecules 18 04403 i038
2-(Pyridin-2-yl)phenyl 2-methylbenzoate (2o). Yellow oil (66% yield). 1H-NMR (CDCl3): δH 8.61 (dd, J = 4.8, 0.8 Hz, 1H), 8.01 (dd, J = 7.1, 1.3 Hz, 1H), 7.76 (dd, J = 7.6, 1.6 Hz, 1H), 7.64 (dt, J = 7.7, 1.7 Hz, 1H), 7.56 (d, J = 7.9 Hz, 1H), 7.49 (dt, J = 7.7, 1.6 Hz, 1H), 7.38–7.45 (m, 2H), 7.24–7.30 (m, 4H), 7.15–7.19 (m, 1H), 2.54 (s, 3H). 13C-NMR (CDCl3): δC 166.3 (C=O), 156.5 (C), 150.2 (C-O), 150.0 (C-H), 141.8 (C), 136.8 (C-H), 134.2 (C-H), 133.1 (C-H), 132.7 (C-H), 132.4 (C-H), 131.5 (C-H), 130.4 (C), 129.2 (C), 128.5 (C-H), 126.9 (C-H), 126.4 (C-H), 124.1 (C-H), 122.8 (C-H), 22.2 (CH3). MS (EI): 289 (M+, 10), 119 (100), 91 (40). HRMS (ESI): calcd. for C19H15NO2H+: 290.1181, found: 290.1186. IR (KBr, cm−1): 1738.
Molecules 18 04403 i039
2-(Pyridin-2-yl)phenyl 4-methylbenzoate (2p). Yellow oil (64% yield). 1H-NMR (CDCl3): δH 8.60 (d, J = 4.7 Hz, 1H), 7.98 (d, J = 8.1 Hz, 2H), 7.79 (dd, J = 7.7, 1.5 Hz, 1H), 7.55–7.60 (m, 2H), 7.47 (dt, J = 7.7, 1.5 Hz, 1H), 7.39 (t, J = 7.5 Hz, 1H), 7.25 (d, J = 7.9 Hz, 2H), 7.14–7.16 (m, 1H), 7.04 (t, J = 4.7 Hz, 1H), 2.41 (s, 3H). 13C-NMR (CDCl3): δC 165.8 (C=O), 156.2 (C), 150.2 (C-O), 149.4 (C-H), 144.9 (C), 136.7 (C-H), 134.0 (C-H), 131.5 (C-H), 130.7 (C-H), 130.1 (C-H), 129.6 (C), 127.3 (C), 126.9 (C-H), 124.4 (C-H), 124.0 (C-H), 122.7 (C-H), 22.3 (CH3). MS (EI): 289 (M+, 10), 119 (100), 91 (40). HRMS (ESI): calcd. for C19H15NO2H+: 290.1181, found: 290.1173. IR (KBr, cm−1): 1737.
Molecules 18 04403 i040
2-(Pyridin-2-yl)phenyl 4-fluorobenzoate (2q). Yellow oil (55% yield). 1H-NMR (CDCl3): δH 8.57 (d, J = 4.2 Hz, 1H), 8.08–8.11 (m, 2H), 7.76 (dd, J = 7.6, 1.5 Hz, 1H), 7.62 (dt, J = 7.7, 1.6 Hz, 1H), 7.53 (d, J = 7.9 Hz, 1H), 7.47 (dt, J = 7.7, 1.5 Hz, 1H), 7.39 (dt, J = 7.5, 0.9 Hz, 1H), 7.30 (dd, J = 7.9, 0.8 Hz, 1H), 7.09–7.16 (m, 3H). 13C-NMR (CDCl3): δC 167.9 (C-F), 164.8 (C=O), 156.1 (C), 150.1 (C-O), 148.8 (C-H), 136.8 (C-H), 133.9 (C-H), 133.4 (C-H), 131.5 (C-H), 130.3 (C), 127.1 (C-H), 126.3 (C), 123.0 (C-H), 122.8 (C-H), 116.4 (C-H), 116.2 (C-H). MS (EI): 293 (M+, 10), 123 (100), 95 (30). HRMS (ESI): calcd. for C18H12NO2FH+: 294.0930, found: 294.0931. IR (KBr, cm−1): 1738.
Molecules 18 04403 i041
2-(Pyridin-2-yl)phenyl 4-bromobenzoate (2r). Yellow oil (30% yield). 1H-NMR (CDCl3): δH 8.56 (d, J = 4.3 Hz, 1H), 7.94 (d, J = 8.5 Hz, 2H), 7.76 (dd, J = 7.6, 1.4 Hz, 1H), 7.64 (dd, J = 7.8, 1.6 Hz, 1H), 7.46–7.53 (m, 3H), 7.40 (t, J = 7.0 Hz, 1H), 7.30 (d, J = 7.8 Hz, 1H), 7.14–7.17 (m, 1H). 13C-NMR (CDCl3): δC 165.1 (C=O), 156.2 (C), 150.2 (C-O), 148.8 (C-H), 136.9 (C-H), 133.8 (C-H), 132.5 (C-H), 132.3 (C-H), 131.9 (C-H), 130.4 (C-H), 129.3 (C), 129.1 (C), 127.2 (C-Br), 124.2 (C-H), 123.9 (C-H), 122.8 (C-H). MS (EI): 355 (M+, 20), 183 (100), 155 (20). HRMS (ESI): calcd. for C18H12NO2BrH+: 354.0130, found: 354.0133. IR (KBr, cm−1): 1737.
Molecules 18 04403 i042
2-(Pyridin-2-yl)phenyl 4-(trifluoromethyl)benzoate (2s). Yellow oil (81% yield). 1H-NMR (CDCl3): δH 8.54 (d, J = 4.5 Hz, 1H), 8.19 (d, J = 8.4 Hz, 2H), 7.71–7.82 (m, 3H), 7.64 (dt, J = 7.8, 1.7 Hz, 1H), 7.47–7.54 (m, 2H), 7.41 (dt, J = 7.5, 1.0 Hz, 1H), 7.31 (d, J = 8.0 Hz, 1H), 7.14–7.17 (m, 1H). 13C-NMR (CDCl3): δC 164.7 (C=O), 156.2 (C), 150.1 (C-O), 148.7 (C-H), 137.0 (C), 135.6 (C-H), 135.2 (C-H), 133.8 (C-H), 133.4 (C), 131.5 (C-H), 131.2 (C-H), 130.5 (C), 127.3 (C-H), 125.6 (C-H), 124.1 (CF3), 123.9 (C-H), 122.9 (C-H). MS (EI): 343 (M+, 40), 173 (100), 145 (50). HRMS (ESI): calcd. for C19H12NO2F3H+: 344.0898, found: 344.0901. IR (KBr, cm−1): 1743.
Molecules 18 04403 i043
2-(Pyridin-2-yl)phenyl 4-ethoxybenzoate (2t). Yellow oil (27% yield). 1H-NMR (CDCl3): δH 8.61 (d, J = 4.6 Hz, 1H), 8.02 (d, J = 8.8 Hz, 2H), 7.78 (dd, J = 7.6, 1.3 Hz, 1H), 7.54–7.63 (m, 2H), 7.47 (dt, J = 7.6, 1.3 Hz, 1H), 7.38 (dt, J = 7.5, 0.9 Hz, 1H), 7.29 (d, J = 8.1 Hz, 1H), 7.13–7.17 (m, 1H), 6.91 (d, J = 8.8 Hz, 2H), 4.09 (q, J = 7.0 Hz, 2H), 1.44 (t, J = 7.0 Hz, 1H). 13C-NMR (CDCl3): δC 165.5 (C=O), 163.9 (C-O), 156.2 (C), 150.3 (C-O), 149.1 (C-H), 136.7 (C-H), 134.0 (C-H), 133.0 (C-H), 131.5 (C-H), 130.3 (C), 126.9 (C-H), 124.4 (C-H), 124.1 (C-H), 122.7 (C-H), 122.2 (C), 114.9 (C-H), 64.4 (CH2), 15.3 (CH3). MS (EI): 319 (M+, 10), 207 (20), 149 (100), 121 (40). HRMS (ESI): calcd. for C20H17NO3H+: 320.1287, found: 320.1285. IR (KBr, cm−1): 1731.
Molecules 18 04403 i044
2-(Pyridin-2-yl)phenyl 4-tert-butylbenzoate (2u). Yellow oil (77% yield). 1H-NMR (CDCl3): δH 8.62 (d, J = 4.6 Hz, 1H), 8.04 (d, J = 8.3 Hz, 2H), 7.88 (d, J = 8.3 Hz, 2H), 7.45–7.54 (m, 2H), 7.36–7.42 (m, 2H), 7.11–7.14 (m, 1H), 1.33 (d, J = 13.6 Hz, 9H). 13C-NMR (CDCl3): δC 165.2 (C=O),157.7 (C), 156.1 (C-O), 149.9 (C), 148.9 (C-H), 136.7 (C-H), 133.9 (C-H), 131.5 (C-H), 130.5 (C-H), 130.2 (C), 126.8 (C), 125.9 (C-H), 124.3 (C-H), 123.9 (C-H), 122.6 (C-H), 121.2 (C-H), 35.6 (C), 31.6 (CH3). MS (EI): 331 (M+, 10), 161 (100), 146 (10). HRMS (ESI): calcd. for C22H21NO2H+: 332.1651, found: 332.1652. IR (KBr, cm−1): 1737cm−1.
Molecules 18 04403 i045
2-(Pyridin-2-yl)phenyl 2,6-difluorobenzoate (2v). Yellow oil (46% yield). 1H-NMR (CDCl3): δH 8.65 (d, J = 4.4 Hz, 1H), 7.76 (dd, J = 7.6,1.6 Hz, 1H), 7.70 (dt, J = 7.7, 1.7 Hz, 1H), 7.59 (d, J = 7.9 Hz, 1H), 7.49 (dt, J = 7.7, 1.6 Hz, 1H), 7.39–7.44 (m, 2H), 7.33 (dd, J = 8.0, 1.0 Hz, 1H), 7.20–7.23 (m, 1H), 6.95 (t, J = 8.3 Hz, 2H). 13C-NMR (CDCl3): δC 162.7 (C=O), 160.7 (C-F), 156.0 (C), 150.2 (C-O), 148.3 (C-H), 136.9 (C-H), 134.1 (C-H), 134.0 (C), 131.6 (C-H), 130.5 (C-H), 127.5 (C-H), 124.4 (C-H), 123.7 (C-H), 122.9 (C-H), 112.9 (C), 112.6 (C-H). MS (EI): 311 (M+, 40), 141 (100), 113 (10). HRMS (ESI): calcd. for C18H11NO2F2H+: 312.0836, found: 312.0841. IR (KBr, cm−1): 1751.
Molecules 18 04403 i046
2-(Pyridin-2-yl)phenyl 2-naphthoate (2w). Yellow oil (44% yield). 1H-NMR (CDCl3): δH 8.69 (s, 1H), 8.59 (d, J = 4.8 Hz, 1H), 8.10 (dd, J = 8.6, 1.4 Hz, 1H), 7.95 (d, J = 8.0 Hz, 1H), 7.90 (d, J = 8.5 Hz, 2H), 7.82 (dd, J = 7.6, 1.5 Hz, 1H), 7.56–7.63 (m, 4H), 7.51 (dt, J = 7.8, 1.6 Hz, 1H), 7.41–7.45 (m, 1H), 7.38 (dd, J = 7.9, 0.7 Hz, 1H),7.11–7.15 (m, 1H). 13C-NMR (CDCl3): δC 166.0 (C=O), 156.3 (C), 150.3 (C-O), 149.1 (C-H), 136.8 (C-H), 136.4 (C), 134.0 (C-H), 133.1 (C), 132.6 (C-H), 131.6 (C-H), 130.4 (C-H), 130.1 (C-H), 129.2 (C), 128.9 (C-H), 128.4 (C), 127.4 (C-H), 127.3 (C-H), 127.1 (C-H), 126.1 (C-H), 124.3 (C-H), 124.0 (C-H), 122.8 (C-H). MS (EI): 325 (M+, 20), 155 (100), 127 (60). HRMS (ESI): calcd. for C22H15NO2H+: 326.1181, found: 326.1191. IR (KBr, cm−1): 1734 cm−1.
Molecules 18 04403 i047

4. Conclusions

In summary, we developed a Pd-catalyzed regioselective C–H benzoxylation reaction with aryl acylperoxides as reagents. This catalytic protocol was convenient to operate, and the product benzoates were formed in good yield with high regioselectivity and functional group tolerance.

Supplementary Materials

Supplementary materials can be accessed at: https://www.mdpi.com/1420-3049/18/4/4403/s1.

Acknowledgments

We thank the financial support from The Hong Kong Research Grants Council (PolyU 5031/09P, SEG_PolyU01). And also thank Jin-Quan Yu and Ramesh Giri for the invitation of the submission of this article on the special issue “Transition Metal Catalysis”.

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MDPI and ACS Style

Sit, W.-N.; Chan, C.-W.; Yu, W.-Y. Palladium(II)-Catalyzed othro-C–H-Benzoxylation of 2-Arylpyridines by Oxidative Coupling with Aryl Acylperoxides. Molecules 2013, 18, 4403-4418. https://doi.org/10.3390/molecules18044403

AMA Style

Sit W-N, Chan C-W, Yu W-Y. Palladium(II)-Catalyzed othro-C–H-Benzoxylation of 2-Arylpyridines by Oxidative Coupling with Aryl Acylperoxides. Molecules. 2013; 18(4):4403-4418. https://doi.org/10.3390/molecules18044403

Chicago/Turabian Style

Sit, Wing-Nga, Chun-Wo Chan, and Wing-Yiu Yu. 2013. "Palladium(II)-Catalyzed othro-C–H-Benzoxylation of 2-Arylpyridines by Oxidative Coupling with Aryl Acylperoxides" Molecules 18, no. 4: 4403-4418. https://doi.org/10.3390/molecules18044403

APA Style

Sit, W. -N., Chan, C. -W., & Yu, W. -Y. (2013). Palladium(II)-Catalyzed othro-C–H-Benzoxylation of 2-Arylpyridines by Oxidative Coupling with Aryl Acylperoxides. Molecules, 18(4), 4403-4418. https://doi.org/10.3390/molecules18044403

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