V. T. H. Nguyen, P. Langer / Tetrahedron Letters 46 (2005) 1013–1015
1015
concentrated in vacuo. The residue was purified by
chromatography. Synthesis of 6b: Starting with (2-meth-
oxy)phenylboronic acid (296 mg, 1.95 mmol), potassium
phosphate (509 mg, 2.40 mmol), Pd(PPh3)4 (52 mg,
0.045 mmol), 5b (510 mg, 1.5 mmol) and dioxane (5 mL),
6b was isolated by chromatography (silica gel, n-hexane/
EtOAc = 20:1) as a colourless solid (320 mg, 73%), mp =
92 °C. 1H NMR (300 MHz, CDCl3): d = 2.24 (s, 3H,
CH3), 2.31 (s, 3H, CH3), 2.32 (s, 3H, CH3), 3.51 (s, 3H,
CH3O), 3.74 (s, 3H, CH3O), 6.89 (d, 1H, Ar), 6.92–6.98
(m, 1H, Ar), 7.00 (s, 1H, Ar), 7.14–7.18 (dd, 1H, Ar),
7.28–7.31 (dd, 1H, Ar). 13C NMR (75 MHz, CDCl3):
d = 15.6 (CH3), 17.6 (CH3), 20.9 (CH3), 51.4 (CH3), 55.5
(CH3), 110.5 (CH), 120.3 (CH), 128.6 (CH), 129.8
(CH), 130.0 (C), 130.6 (CH), 131.9 (C), 133.5 (C), 133.9
(C), 134.8 (C), 137.7 (C), 156.4 (C), 170.4 (C). IR (KBr,
Acknowledgements
Financial support from the Ministry of Education
of Vietnam (scholarship for V.T.H.N.) and from
the Deutsche Forschungsgemeinschaft is gratefully
acknowledged.
References and notes
1. Alternariol: (a) Raistrick, H.; Stilkings, C. E.; Thomas, R.
Biochemistry 1953, 55, 421; autumnariol and autumnarin-
iol: (b) Tamm, C. Arzneim.-Forsch. 1972, 22, 1776;
altenuisol: (c) Pero, R. W.; Harvan, D.; Blois, M. C.
Tetrahedron Lett. 1973, 14, 945.
2. (a) Sayer, J. M.; Haruhiko, Y.; Wood, A. W.; Conney, A.
H.; Jerina, D. M. J. Am. Chem. Soc. 1982, 104, 5562; (b)
Gunawardana, Y. A. G. P.; Kumar, N. S.; Sultanbawa,
M. U. S. Phytochemistry 1979, 18, 1017.
3. Alo, B. I.; Kandil, A.; Patil, P. A.; Sharp, M. J.; Siddiqui,
M. A.; Snieckus, V. J. Org. Chem. 1991, 56, 3763, and
Refs. 6–10 cited therein.
4. Hurtley, W. R. H. J. Chem. Soc. 1929, 1870.
5. Harris, T. M.; Hay, J. V. J. Am. Chem. Soc. 1977, 99,
1631.
cmÀ1): m ¼ 2997 (m), 2949 (m), 1719 (s), 1600 (m), 1497 (s),
~
1464 (s), 1436 (s), 1269 (s), 1239 (s), 1634 (s, 1108 (s), 1048
(s), 1269 (s), 1239 (s), 1164 (s), 1108 (s), 1048 (s), 772 (s).
UV–vis (nm): kmax (lg e) = 210.3 (4.59), 281.0 (3.63). MS
(EI, 70 eV): m/z (%) = 285 ([M+1]+, 2), 284 (M+, 17), 253
(21), 210 (43), 182 (15), 152 (4), 28 (100). HRMS (ESI):
calcd for C18H21O3 ([M+1]+): 285.14907. Found:
285.14871.
13. General procedure for the synthesis of 7: To a CH2Cl2
solution of 6 was added BBr3 at 0 °C. The solution was
allowed to warm to 20 °C during 18 h. To the solution was
added an aqueous solution of KO-t-Bu (0.1 M) and the
solution was stirred for 15 min. The organic and the
aqueous layer were separated and the latter was extracted
with CH2Cl2. The combined organic layers were dried
(Na2SO4), filtered and the filtrate was concentrated in
vacuo. The product was purified by chromatography
(silica gel, n-hexane/EtOAc = 25:1) as a colourless solid.
Synthesis of 7b: Starting with 6b (284 mg, 0.95 mmol) in
CH2Cl2 (3 mL), BBr3 (477 mg, 1.9 mmol) and an aqueous
solution of KO-t-Bu (0.1 M, 10 mL), 7b was isolated by
chromatography as a colourless solid (160 mg, 71%),
mp = 184 °C. 1H NMR (300 MHz, CDCl3): d = 2.35 (s,
3H, CH3), 2.49 (s, 3H, CH3), 2.84 (s, 3H, CH3), 7.25–7.32
(m, 2H, Ar), 7.39–7.45 (m, 1H, Ar), 7.81 (s, 1H, Ar), 8.01–
8.05 (dd, 1H, Ar). 13C NMR (75 MHz, CDCl3): d = 16.2
(CH3), 18.4 (CH3), 22.2 (CH3), 116.9 (CH), 117.8 (C),
118.4 (C), 120.5 (CH), 122.6 (CH), 123.9 (CH), 129.6
(CH), 133.2 (C), 137.7 (C), 142.2 (C), 143.7 (C), 151.2 (C),
6. Bringmann, G.; Reuscher, H. Tetrahedron Lett. 1989, 30,
5249.
7. (a) Chan, T.-H.; Brownbridge, P. J. Chem. Soc., Chem.
Commun. 1979, 578; (b) Molander, G. A.; Cameron, K. O.
J. Am. Chem. Soc. 1993, 115, 830.
8. For a review of 1,3-bis-silyl enol ethers, see: Langer, P.
Synthesis 2002, 441.
9. (a) Chan, T.-H.; Brownbridge, P. J. Am. Chem. Soc. 1980,
102, 3534; (b) Brownbridge, P.; Chan, T.-H.; Brook, M.
A.; Kang, G. J. Can. J. Chem. 1983, 61, 688; for
cyclizations of 1,3-bis-silyl enol ethers with 2-acetyl-1-
silyloxybut-1-en-3-one, see: (c) Dede, R.; Langer, P.
Tetrahedron Lett. 2004, 45, 9177.
10. For Suzuki reactions of salicylate derived triflates with
arylboronic acids, see: Schmidt, J. M.; Tremblay, G. B.;
Page, M.; Mercure, J.; Feher, M.; Dunn-Dufault, R.;
Peter, M. G.; Redden, P. R. J. Med. Chem. 2003, 46, 1289.
11. For BBr3 mediated lactonizations, see: (a) Kanakam, C.
C.; Mani, N. S.; Rao, G. S. R. S. J. Chem. Soc., Perkin
Trans. 1 1990, 8, 2233; (b) Coghlan, M. J.; Kym, P. R.;
Elmore, S. W.; Wang, A. X.; Luly, J. R.; Wilcox, D.;
Stashko, M.; Lin, C.-W.; Miner, J.; Tyree, C.; Nakane, M.
J. Med. Chem. 2001, 44, 2879, see also: (c) Ref. 3; for the
use of HBr, see, for example:(d) Manthey, M. K.; Pyne, S.
G.; Truscott, R. J. W. J. Org. Chem. 1990, 55, 4581.
12. General procedure for the synthesis of 6: A dioxane solution
of the boronic acid, potassium phosphate, Pd(PPh3)4 and
of the triflate 4 was stirred at 110 °C for 4 h. After cooling,
a saturated aqueous solution of NH4Cl was added. The
organic and the aqueous layer were separated and the
latter was extracted with CH2Cl2. The combined organic
layers were dried (Na2SO4), filtered and the filtrate was
160.8 (C). IR (KBr, cmÀ1): m ¼ 3428 (m), 2927 (m), 1726
~
(s), 1606 (s), 1473 (s), 1272 (s), 1210 (s), 1119 (s), 1010 (s),
753 (s). UV–vis (nm): kmax (lg e) = 239.5 (4.59), 265.4
(4.06), 275.1 (4.08), 289.7 (3.83), 299.5 (3.92), 322.2 (3.87).
MS (EI, 70 eV): m/z (%) = 239 ([M+1]+, 16), 238 (M+,
100), 223 (28), 195 (17), 165 (11), 151 (5), 28 (21). HRMS
(ESI): calcd for C16H15O2 ([M+1]+): 239.10721. Found:
239.10736. Anal. Calcd for C16H14O2: C, 80.61; H, 5.92.
Found: C, 80.19; H, 6.18.
14. (a) Langer, P.; Bose, G. Angew. Chem. 2003, 115, 4165.
Angew. Chem. 2003, 42, 4033; (b) Bose, G.; Nguyen, V. T.
H.; Ullah, E.; Lahiri, S.; Go¨rls, H.; Langer, P. J. Org.
Chem. 2004, 69, 9128.