F. A. Khan, L. Soma / Tetrahedron Letters 48 (2007) 85–88
87
3. (a) Li, J. J.; Gribble, G. W. Palladium in Heterocyclic
Chemistry; Pergamon: Amsterdam, 2000; (b) Zeni, G.;
Larock, R. C. Chem. Rev. 2004, 104, 2285–2310.
column purification, the crude product was directly
carried forward in the next step in a separate experiment
to obtain an 86% overall yield of 5.
4. (a) Hosokawa, T.; Maeda, K.; Koga, K.; Moritani, I.
Tetrahedron Lett 1973, 14, 739–740; (b) Hosokawa, T.;
Ohkata, H.; Moritani, I. Bull. Chem. Soc. Jpn. 1975, 48,
1533–1536; (c) Hosokawa, T.; Yamashita, S.; Murahashi,
S.-I.; Sonoda, A. Bull. Chem. Soc. Jpn. 1976, 49, 3662–
3665; (d) Hosokawa, T.; Miyagi, S.; Murahashi, S.-I.;
Sonoda, A. J. Org. Chem. 1978, 43, 2752–2757; (e)
Hosokawa, T.; Uno, T.; Inui, S.; Murahashi, S.-I. J.
Am. Chem. Soc. 1981, 103, 2318–2323; (f) Hosokawa, T.;
Okuda, C.; Murahashi, S.-I. J. Org. Chem. 1985, 50, 1282–
1287; (g) Hosokawa, T.; Imada, Y.; Murahashi, S.-I. Bull.
Chem. Soc. Jpn. 1985, 58, 3282–3290.
In summary, tribromobenzofuran derivative 5 and tri-
bromobenzopyran derivative 6 were obtained in good
yields via palladium(II)-catalyzed oxidative cyclization
of methyl 2-allyl-4,5,6-tribromo-3-hydroxybenzoate 4.
A complete reversal in the regioselectivity (71:29 to
24:76) was observed by changing the catalyst cocktail.
On the other hand, electrophilic cyclization mediated
by NBS or NIS followed by base treatment led exclu-
sively to benzofuran derivative 5.
5. Roshchin, A. I.; Kel’chevski, S. M.; Bumagin, N. A. J.
Organomet. Chem. 1998, 560, 163–167.
6. Larock, R. C.; Wei, L.; Hightower, T. R. Synlett 1998,
522–524.
Acknowledgements
7. Khan, F. A.; Dash, J.; Jain, D.; Prabhudas, B. J. Chem.
Soc., Perkin Trans. 1 2001, 3132–3134.
8. Khan, F. A.; Choudhury, S. Eur. J. Org. Chem. 2006, 672–
676.
Financial support from the Department of Science and
Technology (DST), New Delhi, is gratefully acknowl-
edged. F.A.K. acknowledges the DST for a Swarnajay-
anti Fellowship. L.S. thanks CSIR, New Delhi, for a
fellowship.
9. (a) Gribble, G. W.; Field, J. A.; Wijnberg, J. B. P. A.
Natural Production of Organohalogen Compounds. In
The Handbook of Environmental Chemistry; Hutzinger, O.,
Gribble, G. W., Eds.; Springer: New York, 2003; Vol. 3,
part P, pp 1–15, 103–119; (b) Gribble, G. W. Naturally
Occurring Organohalogen Compounds—A Comprehen-
sive Survey. In Progress in the Chemistry of Organic
Natural Products; Herz, W., Kirby, G. W., Moore, R. E.,
Steglich, W., Tamm, Ch., Eds.; Springer Wien: New York,
1996; Vol. 68, (c) Gribble, G. W. Chem. Soc. Rev. 1999,
28, 335–346.
References and notes
1. (a) Hou, X.-L.; Yang, Z.; Wong, H. N. C. Furans and
Benzofurans. In Progress in Heterocyclic Chemistry;
Gribble, G. W., Gilchrist, T. L., Eds.; Pergamon: Oxford,
2002; Vol. 14, pp 139–179; (b) Fatome, M.; Andrieu, L.;
Laval, J.-D. Eur. J. Med. Chem. 1977, 383–384; (c)
Shiratsuchi, M.; Kawamura, K.; Akashi, T.; Fujii, M.;
Ishihama, H.; Uchida, Y. Chem. Pharm. Bull. 1987, 35,
632–641; (d) McCallion, G. D. Curr. Org. Chem. 1999, 3,
67–76; (e) Bates, R. W.; Devi, T. R. Synlett 1995, 1151–
1152; (f) Hiroya, K.; Hashimura, K.; Ogasawara, K.
Heterocycles 1994, 2463–2472.
2. (a) Mustafa, A. Benzofurans. In The Chemistry of
Heterocyclic Compounds; Weissberger, A., Taylor, E. C.,
Eds.; John Wiley & Sons: New York, 1974; Vol. 29, (b)
Fringuelli, F.; Taticchi, A. The Diels–Alder Reaction
Selected Practical Methods; John Wiley & Sons: West
Sussex, 2002; p 57; (c) Larock, R. C.; Stinn, D. E.
Tetrahedron Lett. 1988, 29, 4687–4690; (d) Xie, X.; Chen,
B.; Lu, J.; Han, J.; She, X.; Pan, X. Tetrahedron Lett.
2004, 45, 6235–6237; (e) Hennings, D. D.; Iwasa, S.;
Rawal, V. H. Tetrahedron Lett. 1997, 38, 6379–6382; (f)
Mphahlele, M. J.; Moekwa, T. B. Org. Biomol. Chem.
2005, 3, 2469–2475; (g) Sanz, R.; Castroviejo, M. P.;
Fernandez, Y.; Fananas, F. J. J. Org. Chem. 2005, 70,
6548–6551; (h) Furstner, A.; Davies, P. W. J. Am. Chem.
Soc. 2005, 127, 15024–15025; (i) Patel, V. F.; Pattenden,
G.; Russell, J. J. Tetrahedron Lett. 1986, 27, 2303–2306; (j)
van Otterlo, W. A. L.; Ngidi, E. L.; de Koning, C. B.
Tetrahedron Lett. 2003, 44, 6483–6486; (k) Grubbs, R. H.;
Chang, S. J. Org. Chem. 1998, 63, 864–866; (l) Barluenga,
J.; Trincado, M.; Marco-Arias, M.; Ballesteros, A.; Rubio,
E.; Gonzalez, J. M. Chem. Commun. 2005, 2008–2010; (m)
North, J. T.; Kronenthal, D. R.; Pullockaran, A. J.; Real,
S. D.; Chen, H. Y. J. Org. Chem. 1995, 60, 3397–3400; (n)
Tiabi, M.; Zamarlik, H. Tetrahedron Lett. 1991, 32, 7251–
7252; (o) Garcias, X.; Ballester, P.; Saa, J. M. Tetrahedron
Lett. 1991, 32, 7739–7742; (p) Schuda, P. F.; Phillips, J. L.
J. Heterocycl. Chem. 1984, 21, 669–672.
10. Illustrative procedure for the palladium(II)-catalyzed
oxidative cyclization of 4 (Table 1, entry 6): o-allylic
phenol derivative 4 (100 mg, 0.23 mmol), LiCl (30 mg,
0.70 mmol), and PdCl2 (1.6 mg, 4 mol %) were added to a
solution of Cu(OAc)2ÆH2O (140 mg, 0.70 mmol) in DMF–
H2O (4 mL:0.1 mL). The suspension was stirred under
atmospheric air at 55–60 ꢁC for 2.5 h. The reaction
mixture was diluted with 20 mL of water containing
5 mL of aq 25% ammonia solution and then extracted
with diethyl ether (3 · 15 mL). The combined organic
layers were sequentially washed with aq 25% NaOH
solution (10 mL), water (15 mL), and brine (15 mL), dried
over anhydrous Na2SO4 and evaporated. The residue was
purified by column chromatography (silica gel pretreated
with 7% AgNO3) to afford 5 (19.7 mg, 20%) and 6 (63 mg,
63%). Overall yield: 83% (ratio 5:6 = 24:76). Compound 5:
colorless crystalline solid; mp 119–121 ꢁC; 1H NMR
(400 MHz, CDCl3): d 6.46 (d, 1H, J = 1.0 Hz), 3.92 (s,
3H, OMe), 2.43 (s, 3H, Me); 13C NMR (100 MHz,
CDCl3): d 166.0, 159.3, 151.7, 128.8, 125.6 123.2, 117.6,
110.4, 103.6, 52.7, 14.1; IR (KBr): 1730, 1600, 1240, 1150,
810 cmꢀ1; Anal. Calcd for C11H7Br3O3: C, 30.95; H, 1.65.
Found: C, 31.25; H, 1.76. Compound 6: white solid; mp
1
94–96 ꢁC; H NMR (400 MHz, CDCl3): d 6.21–6.18 (td,
1H, J = 10.0, 1.9 Hz), 5.89–5.85 (td, 1H, J = 10.0, 3.4 Hz),
4.91–4.90 (dd, 2H, J = 3.4, 1.9 Hz), 3.88 (s, 3H, OMe); 13
C
NMR (100 MHz, CDCl3): d 166.4, 151.0, 132.8, 128.3,
125.1, 120.6, 120.0, 115.7, 113.4, 66.5, 53.0; IR (KBr):
1720, 1410, 1250, 1190, 1160, 1050, 980 cmꢀ1; Anal. Calcd
for C11H7Br3O3: C, 30.95; H, 1.65. Found: C, 30.56; H,
1
1.71. Compound 7a: white solid; mp 56–57 ꢁC; H NMR
(400 MHz, CDCl3): d 5.13–5.06 (m, 1H), 3.88 (s, 3H,
OMe), 3.59–3.56 (dd, 1H, J = 10.7, 4.2 Hz), 3.52–3.43 (m,
2H), 3.25–3.19 (dd, 1H, J = 17.0, 6.6 Hz); 13C NMR
(100 MHz, CDCl3): d 165.9, 157.2, 131.3, 128.4, 125.9,