N. R. Jogdand et al. / Tetrahedron Letters 50 (2009) 4019–4021
4021
yields as compared to 1,4-dioxane. Hence, dioxane as a solvent in
References and notes
combination with Cs2CO3 as a base works well for this coupling
protocol.
1. (a) Evans, D. A.; DeVries, M. K. InGlycopeptide Antibiotics;Nagarajan, R., Ed.;Drugs
and the Pharmaceutical Sciences; Marcel Decker: New York, 1994; p 63; (b)
Eicher, T.; Fey, S.; Puhl, W.; Buchel, E.; Speicher, A. Eur. J. Org. Chem. 1998, 877; (c)
Evans, D. A.; Wood, M. R.; Trotter, B. W.; Richardson, T. I.; Barrow, J. C.; Katz, J. L.
Angew. Chem., Int. Ed. 1998, 37, 2700; (d) Evans, D. A.; Dinsmore, C. J.; Watson, P.
S.; Wood, M. R.; Richardson, T. I.; Trotter, B. W.; Katz, J. L. Angew. Chem., Int. Ed.
1998, 37, 2704; (e) Zhang, A. J.; Burgess, K. Angew. Chem., Int. Ed. 1999, 38, 634; (f)
Islas-Gonzalez, G.; Bois-Choussy, M. Z. J. Org. Biomol. Chem. 2003, 1, 30.
2. Theil, F. Angew. Chem., Int. Ed. 1999, 38, 2345.
3. Ley, S. V.; Thomas, A. W. Angew. Chem., Int. Ed. 2003, 42, 5400.
4. (a) Ullmann, F. Chem. Ber. 1904, 37, 853; (b) Lindley, J. Tetrahedron 1984, 40,
1433. and the references cited therein.
5. Mann, G.; Hartwig, J. F. Tetrahedron Lett. 1997, 38, 8005.
6. Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadhigi, J. P.; Buchwald, S. L. J.
Am. Chem. Soc. 1999, 121, 4369.
Table 2 shows that the reaction is equally facile with both elec-
tron-donating and electron-withdrawing substituents present on
the aryl ring of aryl halide resulting in good yields of diaryl ethers.
ortho-Substituted iodides (Table 2, entries 3–5) reacted smoothly
with the respective phenols to give isolated diaryl ethers in 80%,
81% and 83% yields, respectively. The electron-withdrawing sub-
strates on the part of aryl halides (Table 2, entries 8 and 9) facili-
tated diaryl ether formation in 88% and 89% yields, respectively.
The strong electron-donating substrates also afforded the desired
product in 82%,19 80% and 83% (Table 2, entries 6, 7 and 11) yields,
respectively. Unfortunately, the electron-withdrawing substrate on
the part of phenol (Table 2, entry 10) was not found to afford diaryl
ether with aryl iodide.
In addition to aryl iodides, we were delighted to note that
aryl bromides could also be used as efficient substrates under
the present diaryl etherification protocol (Table 2, entries 12–
15). Moreover, aryl bromide that bears an electron-withdrawing
group (Table 2, entry 14) is an equally viable substrate without
much rise in the reaction time and temperature. Electron-donat-
ing substrates however, show a marginal decline in the yields
(Table 2, entry 15). Hence, it is quite evident that the present
protocol is viable enough for the O-arylation of phenols using
otherwise less reactive aryl bromides.13 The products obtained
by this method have been well characterized by physical and
spectroscopic data.
7. Lu, X.; Bao, W. J. Org. Chem. 2007, 72, 3863.
8. Lipshutz, B. H.; Unger, J. B.; Taft, B. R. Org. Lett. 2007, 9, 1089.
9. Marcoux, J.-F.; Doye, S.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 119, 10539.
10. Schareina, T.; Zapf, A.; Cotte, A.; Muller, N.; Beller, M. Tetrahedron Lett. 2008, 49,
1851.
11. Miao, T.; Wang, L. Tetrahedron Lett. 2007, 48, 95.
12. Buck, E.; Song, Z. J.; Tschaen, D.; Dormer, P. J.; Volante, R. P.; Reider, P. J. Org.
Lett. 2002, 4, 1623.
13. Naidu, A. B.; Raghunath, O. R.; Prasad, D. J. C.; Sekar, G. Tetrahedron Lett. 2008,
49, 1057.
14. Fagan, P. J.; Hauptman, E.; Shapiro, R.; Casalnuovo, A. J. Am. Chem. Soc. 2000,
122, 5043.
15. For recent copper-catalyzed direct coupling reactions of aryl halides and
phenols, see: (a) Palomo, C.; Oiarbide, M.; Lopez, R.; Gomez-Bengoa, E. Chem.
Commun. 1998, 2091; (b) Kalinin, A. V.; Bower, J. F.; Riebel, P.; Snieckus, V. J.
Org. Chem. 1999, 64, 2986; (c) Gujadhur, R. K.; Bates, C. G.; Venkataraman, D.
Org. Lett. 2001, 3, 4315; (d) Ma, D.; Cai, Q. Org. Lett. 2003, 5, 3799; (e) Cristau,
H.-J.; Cellier, P. P.; Hamada, S.; Spindler, J.-F.; Taillefer, M. Org. Lett. 2004, 6,
913; (f) Ouali, A.; Spindler, J.-F.; Cristau, H.-J.; Taillefer, M. Adv. Synth. Catal.
2006, 348.
In summary, we have demonstrated that tris-(2-amino-
ethyl) amine is a novel, efficient and commercially available
ready to use tripodal ligand that can be used for diaryl ether-
ification in combination with an air-stable and inexpensive
CuI salt. Notably, we have demonstrated that the present pro-
tocol is equally facile with aryl bromides and tolerant of a
range of functional groups. Further studies to investigate the
applications of tris-(2-aminoethyl) amine as a ligand are in
progress.
16. Bernardo, P. D.; Zanonato, P. L.; Melchior, A.; Portanova, R.; Tolazzi, M.;
Choppin, G. R.; Wang, Z. Inorg. Chem. 2008, 47, 1115.
17. Barre, G.; Tanton, D.; Lastecoueres, D.; Vincent, J.-M. J. Am. Chem. Soc. 2004, 126,
7764.
18. Chen, Y.-J.; Chen, H.-H. Org. Lett. 2006, 8, 5609.
19. Representative procedure: Coupling of 1-iodo-4-methoxy benzene and phenol
(Table 2, entry 6): Into a 25 ml capacity one neck round-bottomed flask was
charged dioxane (3 ml) followed by ligand L (0.085 mmol), CuI (0.085 mmol),
1-iodo-4-methoxy benzene (0.85 mmol), phenol (1.02 mmol) and Cs2CO3
(2.04 mmol). The reaction mixture was stirred with a magnetic stir bar and
heated to 110 °C in an oil bath for 24 h. The completion of the reaction was
monitored by TLC. After the consumption of 1-iodo-4-methoxybenzene is
complete, the reaction mixture was cooled to room temperature and water
(ꢀ15 ml) was added. The crude mixture was extracted with ethyl acetate and
purified by column chromatography on silica gel to afford 4-methoxy-diphenyl
ether (0.140 g, 82%) as colourless oil; Rf 0.68 (in hexane). 1H NMR (CDCl3,
200 MHz) d 7.29–7.41 (m, 2H), 6.90–7.11 (m, 7H) and (3.82 (s, 3H); 13C NMR
(CDCl3, 50 MHz) d 158.6, 156.0, 150.2, 129.7, 122.5, 120.9, 117.7, 115.0, 55.7.
The spectroscopic data are in full agreement with those described in the
literature.15d,e
Acknowledgement
We are thankful to the Head, Department of Chemistry, Dr.
Babasaheb Ambedkar Marathwada University, Aurangabad, for
providing laboratory facilities.