Regioselective arylation of benzanilides with aryl triflates or bromides under palladium catalysis

Article abstract of DOI:10.1016/S0040-4039(00)00238-0

Benzanilides efficiently undergo diarylation upon treatment with aryl triflates or bromides in the presence of a palladium-based catalyst system to give the corresponding N-(2,6-diarylbenzoyl)anilines in good to excellent yields. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00238-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 2655–2658
Regioselective arylation of benzanilides with aryl triflates or
bromides under palladium catalysis
Yoko Kametani, Tetsuya Satoh, Masahiro Miura ∗ and Masakatsu Nomura
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Received 17 January 2000; revised 31 January 2000; accepted 4 February 2000
Abstract
Benzanilides efficiently undergo diarylation upon treatment with aryl triflates or bromides in the presence of
a palladium-based catalyst system to give the corresponding N-(2,6-diarylbenzoyl)anilines in good to excellent
yields. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: anilides; arylation; aryl halides; palladium; palladium compounds.
Palladium-catalyzed arylation reactions using aryl halides and their synthetic equivalents including
aryl triflates are now recognized to be of genuine synthetic utility.1 The reactions with various arylmetal
species, especially with arylboronic acids (the Suzuki–Miyaura coupling), are often employed for the
preparation of unsymmetrical biaryls. Meanwhile, we recently reported that (a) mono- and/or diarylation
reactions of phenolic compounds such as 1-naphthols and 2-phenylphenols with aryl halides using a
palladium catalyst can regioselectively occur on their unactivated 8- and 20-positions, respectively,2 and
(b) benzyl phenyl ketones undergo arylation on the two ortho-positions of the carbonyl group as well
as the α-position to give diphenymethyl 2,6-diphenylphenyl ketone derivatives.3 The coordination of
phenolate or enolate oxygen of the substrates to intermediary arylpalladium species is considered to be
the key for these reactions.2,3 Thus, for further development of the new catalytic coupling, it seems to
be crucial to find effective functional groups other than enolate oxygen. Consequently, we examined the
reactions of aryl bromides or triflates with benzoic acid, benzenesulfonanilide and benzamide which have
different acidities.4,5 As a result, we observed that the third compound, which is the least acidic among
the substrates, can efficiently undergo diarylation to give N-(2,6-diphenylbenzoyl)aniline (Table 1). Note
that 2,6-diarylbenzoic acid derivatives are useful building blocks for preparing cyclophanes and related
cyclic compounds having a terphenyl moiety with functionality.6
When benzanilide (1a) (1 mmol) was treated with phenyl triflate (2a) (4 mmol) in the presence of
Pd(OAc)2 (0.05 mmol), PPh3 (0.3 mmol, P/Pd=6) and Cs2CO3 (4 mmol) in DMF at 110°C for 24 h,
a mixture of N-(2-phenylbenzoyl)aniline (4) (48%) and N-(2,6-diphenylbenzoyl)aniline (5) (37%) was
∗
Corresponding author. Fax: +81 6 6879 7362; e-mail: miura@ap.chem.eng.osaka-u.ac.jp (M. Miura)
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00238-0
tetl 16518

2656
Table 1
Reaction of benzanilide (1a) with phenyl triflate (2a) or bromobenzene (3a)a
produced, the starting material 1a (14%) being recovered (entry 1 in Table 1). The reaction in toluene
in place of DMF proceeded much more smoothly, giving the diphenylated compound 5 in a yield of
96% (entry 2). The ratio of PPh3 to Pd(OAc)2 was also found to affect the reaction. The yield of 5 was
reduced by decreasing the P/Pd ratio to 4 (entry 3). The reaction became slower at the ratio of 8, while 5
was obtained in 94% yield after 47 h (the ratio of 4:5 at 24 h was ca. 1:2) (entry 4). The reaction using
bromobenzene (3a) was considerably slower than that using 2a. However, an acceptable yield of 5 (80%)
was obtained in the reaction in o-xylene at 150°C.
Table 2 summarizes results for the reactions of a number of benzanilides 1a–e with triflates 2a,b
and bromide 3b.7,8 N-(4-Methoxybenzoyl)- and N-(4-chlorobenzoyl)anilines (1b,c) and N-benzoyl-4-
methylaniline (1d) reacted with 2a to give the corresponding diphenylated products 6–8 in excellent
yields (entries 1–3). From the reaction of N-(2-methylbenzoyl)aniline (1e) with 2a was obtained the
expected mono-phenylated compound 9 (entry 4). The reactions of 1a with 4-methylphenyl triflate (2b)
and 4-bromochlorobenzene (3b) also afforded diarylated compounds 10 and 11 (entries 5 and 6). In these
reactions using 2b and 3b, P(4-MeC6H4)3 and P(4-ClC6H4)3 were used as ligands in place of PPh3 in
order to avoid the contamination of phenyl group from the phosphine.9
It has been reported that (a) acetanilide undergoes palladation at the ortho-position of the aniline
moiety upon treatment with Pd(OAc)2,10 and (b) intramolecular cyclization of haloamides forming a
C–N bond takes place in the presence of a palladium catalyst.11 No products arylated at the N-phenyl
group and amide nitrogen of 1 were, however, detected in the present reaction. While further studies
are required to discuss the detailed mechanism of the arylation, it may be reasonable to consider that
the coordination of amide anion generated from 1 to intermediary arylpalladium species occurs as the
key step, which is similar to the reactions of phenols and phenyl ketones.2,3 In consistent with this, a

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Table 2
Reaction of benzanilides 1a–e with aryl triflates 2a,b or bromide 3ba

2658
preliminary investigation into the mechanism using N-propylbenzamide and N,N-dimethylbenzamide
suggested that an amide hydrogen is required for the reaction to take place: the former compound
could react with 2a in toluene to give a mixture of mono- and diphenylated products (35% and 14%,
respectively, by GC), whereas the latter gave no coupling products.
References
1. (a) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic Press: New York, 1985. (b) Tsuji, J. Palladium Reagents
and Catalysts; Wiley: Chichester, 1995. (c) Metal-Catalyzed Cross-Coupling Reactions; Diederich, F.; Stang, P. J., Eds.
Wiley–VCH: Weinheim, 1997.
2. (a) Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. Angew. Chem., Int. Ed. Engl. 1997, 36, 1740–1742. (b) Satoh, T.; Inoh,
J.-I.; Kawamura, Y.; Kawamura, Y.; Miura, M.; Nomura, M. Bull. Chem. Soc. Jpn. 1998, 71, 2239–2246. (c) Kawamura, Y.;
Satoh, T.; Miura, M.; Nomura, M. Chem. Lett. 1999, 961–962.
3. Satoh, T.; Kametani, Y.; Terao, Y.; Miura, M.; Nomura, M. Tetrahedron Lett. 1999, 40, 5345–5348.
4. Pd/Cu-catalyzed coupling of N-(2-phenylphenyl)benzenesulfonamides and benzoic acids with alkenes: Miura, M.; Tsuda,
T.; Satoh, T.; Pivsa-Art, S.; Nomura, M. J. Org. Chem. 1998, 63, 5211–5215.
5. Rh-catalyzed arylation of 2-phenylpyridine with arylstannanes: Oi, S.; Fukita, S.; Inoue, Y. Chem. Commun. 1998,
2439–2440.
6. (a) Bryant, J. A.; Helgeson, R. C.; Knobler, C. B.; deGrandpre, M. P.; Cram, D. J. J. Org. Chem. 1990, 55, 4622–4634. (b)
Lüning, U.; Wangnick, C. Liebigs Ann. Chem. 1992, 481–484. (c) Hart, H.; Rajakumar, P. Tetrahedron 1995, 51, 1313–1336.
7. Typical procedure: a mixture of 1a (197 mg, 1 mmol), 2a (904 mg, 4 mmol), Pd(OAc)2 (11.2 mg, 0.05 mmol), PPh3 (78
mg, 0.3 mmol), Cs2CO3 (1.30 g, 4 mmol) and toluene (8 cm3) was stirred under nitrogen at 110°C for 24 h. After cooling,
the reaction mixture was poured into dilute HCl, extracted with ethyl acetate and dried over sodium sulfate. Evaporation of
the solvent and washing the residual solid well with hexane gave product 5 (335 mg, 96%). Mp 279–280°C; 1H NMR (400
MHz, DMSO-d6) δ=6.95 (t, J=7.3 Hz, 1H), 7.15 (t, J=7.3 Hz, 2H), 7.20 (d, J=7.3 Hz, 2H), 7.29 (d, J=7.3 Hz, 2H), 7.36 (t,
J=7.3 Hz, 4H), 7.43 (d, J=7.8 Hz, 2H), 7.50 (d, J=7.3 Hz, 4H), 7.60 (t, J=7.8 Hz, 1H), 10.14 (s, 1H); 13C NMR (100 MHz,
DMSO-d6) δ=120.01, 123.66, 127.46, 128.25, 128.53, 128.63, 129.06, 129.11, 136.49, 138.62, 139.53, 140.38, 166.76; MS
m/z 349 (M+). Anal. calcd for C25H19NO: C, 85.93; H, 5.48; N, 4.01. Found: C, 85.83; H, 5.49; N, 4.00.
8. Selected data for 6: mp 240–242°C; 13C NMR (100 MHz, CDCl3) δ=55.53, 114.72, 120.43, 124.42, 127.75, 128.43, 128.48,
128.65, 128.67, 137.33, 140.32, 142.25, 159.68, 166.96. Anal. calcd for C26H21NO2: C, 82.30; H, 5.58; N, 3.69. Found: C,
82.16; H, 5.64; N, 3.59. For 7: mp 258–259°C; 13C NMR (100 MHz, CDCl3) δ=120.64, 124.80, 128.17, 128.43, 128.62,
128.75, 129.10, 134.03, 135.06, 136.89, 138.95, 142.13, 166.19. Anal. calcd for C25H18ClNO: C, 78.20; H, 4.70; Cl, 9.24;
N, 3.60. Found: C, 78.13; H, 4.74; Cl, 9.21; N, 3.64. For 8: mp 282–283°C; 13C NMR (100 MHz, CDCl3) δ=20.83, 120.74,
127.62, 128.44, 128.59, 129.22, 129.31, 129.36, 134.30, 134.52, 135.64, 140.26, 140.33, 166.96. Anal. calcd for C26H21NO:
C, 85.92; H, 5.82; N, 3.85. Found: C, 85.73; H, 5.90; N, 3.79. For 9: mp 137–138°C; 13C NMR (100 MHz, CDCl3) δ=19.68,
120.45, 124.66, 127.40, 127.62, 128.46, 128.57, 128.80, 129.35, 129.56, 136.14, 136.17, 137.31, 139.22, 140.18, 167.93.
Anal. calcd for C20H17NO: C, 83.60; H, 5.96; N, 4.87. Found: C, 83.46; H, 6.03; N, 4.88. For 10: mp 269–270°C; 13C NMR
(100 MHz, CDCl3) δ=21.14, 120.55, 124.48, 128.43, 128.68, 129.17, 129.19, 129.37, 135.44, 137.30, 137.31, 137.34,
140.30, 167.31. Anal. calcd for C27H23NO: C, 85.91; H, 6.14; N, 3.71. Found: C, 85.56; H, 6.24; N, 3.69. For 11: mp
>290°C; 13C NMR (100 MHz, CDCl3) δ=120.57, 124.99, 128.72, 128.92, 129.51, 129.61, 130.05, 134.15, 135.74, 137.05,
138.52, 139.34, 166.61. Anal. calcd for C25H17Cl2NO: C, 71.78; H, 4.10; Cl, 16.95; N, 3.35. Found: C, 71.59; H, 4.18; Cl,
16.76; N, 3.31.
9. Herrmann, W. A.; Brossmer, C.; Reisinger, C.-P.; Riermeier; T. H.; Öffele, K.; Beller, M. Chem. Eur. J. 1997, 3, 1357–1364
and references cited therein.
10. (a) Horino, H.; Inoue, N. J. Org. Chem. 1981, 46, 4416–4422. (b) Tremont, S. J.; Rahman, H. U. J. Am. Chem. Soc. 1984,
106, 5759–5760.
11. (a) Wolf, J. P.; Rennels, R. A.; Buchwald, S. L. Tetrahedron 1996, 52, 7525–7546. (b) Yang, B. H.; Buchwald, S. L. Org.
Lett. 1999, 1, 35–37.