598
M. Guiso et al. / Tetrahedron Letters 43 (2002) 597–598
Scheme 2. (a) N,N,N-Diisopropyl-ethylamine, tert-butyldimethylsilyl-chloride, anhydrous DMF; (b) Ph3PꢀCH2, anhydrous
DMSO (see text); (c) Ac2O/Py. Ref. 18.
We chose to utilise the acetyl derivative 310 because it is
well known that the Heck reaction gives better yield if
phenolic functions are protected.9
11. 3,5-Diacetoxy-stirene 2: 1H NMR (CDCl3) l (Hz): 7.04
(2H, H-4 and H-8) 6.84 (1H, d, J=2.0, H-6); 6.66 (1H,
dd, Jtrans=17.7, Jcis=11.0, H-2); 5.75 (1H, d, Jtrans=17.7,
H-1a); 5.33 (1H, d, Jcis=11.0, H-1b); 2.30 (6H, s, 2CH3-
CO).
The 3,5-diacetoxy-stirene, 2,11 (Scheme 2) was obtained
by acetylation of the 3,5-dihydroxy-stirene 412 which
was achieved by Wittig reaction between 3,5-dihydroxy-
benzaldehyde, 5, previously protected as di-tert-
butyldimethylsilyl-ether 613 and a methylen-triphenyl-
phosphorane solution, prepared by suspending NaH in
anhydrous DMSO as reported by Greenwald et al.14
1
12. 3,5-Dihydroxy-stirene 4: H NMR (CDCl3) l (Hz): 6.56
(1H, dd, Jtrans=17.7, Jcis=10.8); 6.46 (2H, H-4 and H-8);
6.25 (1H, pt, H-6); 5.67 (1H, d, Jtrans=17.7, H–1a); 5.23
(1H, d, Jcis=10.8, H-1b).
13. 3,5-Bis-(tert-butyldimethyl)silyloxy-benzaldehyde 6: 1H
NMR (CDCl3) l 9.86 (1H, s, H-1); 6.98 and 6.92 (1H,
dd, H-3 and H-7); 6.63 (1H, t, H-5); 0.99 (18 H, s, 2
tert-Bu-Si); 0.23 (12H, s, 4 CH3-Si).
The Heck reaction was carried out using 1 mol% of
Pd(OAc)2, based upon the aryl halide, as catalyst, PPh3
as ligand (P/Pd 3.5 mol), Et3N as base and acetonitrile
as solvent.15 The reaction was carried out for about 17
h and the fully acetylated resveratrol 716 was obtained
(70% yield) besides small amounts of partially deacetyl-
ated ones. Subsequently, compound 7 was deacetylated
to obtain resveratrol 1.17
14. Greenwald, R.; Chaykovsky, M.; Corey, E. J. J. Org.
Chem. 1963, 28, 1128–1129.
15. Experimental procedure. Compounds 2 (90 mg) and 3 (85
mg) were dissolved in acetonitrile (2 ml); Et3N (1 ml),
Pd(OAc)2 (0.7 mg) and PPh3 (5.4 mg) were added. The
mixture was stirred under an Ar stream and heated at
85°C for 17 h. Small additional portions of 3, solvent and
base were added during the reaction time and product
formation was checked by thin-layer chromatography on
silica gel (hexane–diethyl ether, 6:4) to follow the disap-
pearance of 2. The mixture was frozen, acidified by
diluting with about 20 ml 1N HCl and twice extracted by
diethyl ether. The organic layer, washed by brine, dried
and evaporated under reduced pressure gave crude 7
which was purified on silica-gel in hexane–diethyl ether,
4:6, by carrying it at the top of the column adsorbed on
silica-gel. The successive removing of acetyl groups was
Acknowledgements
Financial support from MIUR.
References
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a catalytic amount of sodium
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and H-6); 2.27 (3H, s, CH3-CO).
18. All isolated compounds afforded satisfactory elemental
analysis.