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Synlett 2009(10): 1579-1582  
DOI: 10.1055/s-0029-1217333
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

One-Pot Synthesis of Stilbenes from Alcohols through a Wittig-Type Olefination Reaction Promoted by Nickel Nanoparticles

Francisco Alonso*, Paola Riente, Miguel Yus*
Departamento de Química Orgánica, Facultad de Ciencias and Instituto de Química Orgánica (ISO), Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
Fax: +34(96)5903549; e-Mail: falonso@ua.es; e-Mail: yus@ua.es;
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Received 30 January 2009
Publikationsdatum:
02. Juni 2009 (online)

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Abstract

A series of stilbenes has been synthesised in one pot from benzyl alcohols and benzylidenetriphenylphosphorane through a Wittig-type olefination reaction in the presence of nickel nanoparticles.

Key words

alcohols - Wittig - olefination - stilbenes - nickel nanoparticles

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General Procedure for the Wittig-Type Olefination with Alcohols Promoted by Nickel Nanoparticles
n-BuLi (1.6 M, 625 µL, 1.0 mmol) was added dropwise to a suspension of commercially available benzyltriphenyl-phosphonium chloride (583 mg, 1.5 mmol) in THF (2 mL) at 0 ˚C. While the corresponding ylide was being formed (ca. 20 min), nickel(II) chloride (130 mg, 1 mmol) was added over a suspension of lithium (14 mg, 2 mmol) and DTBB (13 mg, 0.05 mmol) in THF (2 mL) at r.t. under argon. The reaction mixture, which was initially dark blue, changed to black indicating that nickel(0) had been formed. After 10 min, the requisite benzyl alcohol (1 mmol) and the initially prepared ylide suspension were added to the NiNP suspension. The reaction mixture was warmed up to reflux and monitored by GLC-MS. The resulting mixture was diluted with EtOAc (10 mL), filtered through a pad containing Celite, and the filtrate was dried over MgSO4. The residue obtained after removal of the solvent (0.02 bar) was purified by column chromatography (silica gel, hexane, or hexane-EtOAc) to give the pure stilbene. The diastereo-meric ratio was determined on the basis of the GC and ¹H NMR analyses.
Stilbene was characterized by comparison of its physical and spectroscopic properties with those of a commercially available sample (Aldrich). 1-(4-Methylphenyl)-2-phenyl-ethene, [²7] 1-(3-methylphenyl)-2-phenylethene, [²8] 1-(2-methylphenyl)-2-phenylethene, [²7] 1-(4-trifluoromethylphenyl)-
-2-phenylethene, [²9] 1-(3-trifluoromethylphenyl)-2-phenyl-ethene, [³0] 1-(4-methoxyphenyl)-2-phenylethene, [³¹] 1-(3-methoxyphenyl)-2-phenylethene, [³¹] 1-(2-methoxyphenyl)-2-phenylethene, [³²] 1-(2-furyl)-2-phenylethene, [³³] 1-(1,3-di-methoxyphenyl)-2-phenylethene, [³¹] and 1-(1,2,3-trimethoxy-phenyl)-2-phenylethene [³4] were characterised by comparison of their physical and spectroscopic data with those described in the literature.

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Following the general procedure but using double the amount of lithium metal (28 mg, 4 mmol) and adding successively the phosphonium salt and the alcohol to the NiNP suspension.

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This assertion is made on the basis that in every redox process a species is oxidised at the same time that the oxidant agent is reduced. In the present case, we assume that dehydrogenation of the alcohol occurs leading to the intermediate aldehyde (the ‘oxidation’ product). However, other species resulting from a reduction step are not detected.