Stilbene from

Large concentrations of halide ions, preferably iodide, favour the formation of /ra/i5-stilbene from benzaldehyde and benzyltriphenylphosphonium halides in methanol with methoxide as base, whereas large concentrations of methoxide ions slightly favour formation of the m-isomer. These effects have been explained by the preferential solvation of P+ by halide ions, leading to greater reversibility of betaine formation. Methoxide ions, on the other hand, are preferentially solvated by methanol. 

For the formation of stilbenes from aryldiazomethanes, Rh2(OAc)4 was shown to be superior to other catalysts such as CufClO or CuBr2 357), LiBr363 or Ce(NH4)2(N03)6 364) in terms of efficiency, Z-selectivity and compatibility with substituents on the aromatic ring of the diazoalkane 358 . Even higher Z-selectivity was provided by the bulky catalyst iodorhodium(III) mew-tetraphenylporphyrin, but reduced yields had to be acknowledged358 . Contrary to copper catalysts, RhjfOAc failed to induce the formation of carbene dimers from secondary aryldiazoalkanes azines were produced instead 358). 

Figure 3.6. Synthesis of chalcone, flavanone, and stilbene from p-coumaric and malonic acids.

Scheme 97 Stilbene from benzalchloride via an a-elimination at cobalt catalysts.

Heo SI, Jin YS, Jung MJ, Wang MH. (2007) Anti-diabetic properties of 2,5-dihydroxy-4,3 -di-(P-D-glucopyranosyloxy)-tra i-stilbene from mulberry Moms bombycis Koidzumi) root in streptozotocin-induced diabetic rats. J Med Food 10 602-607. 

Stilbenes (from the Greek stilbos, glistening, after shiny crystals), are two-ring structures of the C6-C2-C6 type examples are pinosylvin and pinosylvin methyl ether (Fig. 11.2). They play a role as antifeedants for mammals. 

Thiiranes react with benzyne in an efficient synthesis of phenyl vinyl sulfides. The reaction is stereospecific, thus producing ds-(phenylthio)stilbene from cis-2,3-diphenylthiirane and trans-(phenylthio)stilbene from fra .v-2,3-diphenylthiirane (Scheme 24) (84TL2679). 

Figure 3-15. Biosynthesis of stilbene from p-coumaroyl-CoA with three molecules malonyl-CoA, catalyzed by the enzyme stilbene synthase (a E.C. 2.3.1.95).

For general synthetic purposes, any of the direct and sensitized photoisomerization routes can be used in the preparation of (E )-stilbenes from the corresponding (Z)-isomers. However, if really pure (Z)-stilbene 90aZ is required, fluorenone sensitization is highly recommended. Otherwise, trace... 

The quinone methides can also react by elimination of formaldehyde or hydrogen ion at the /3-carbon atom, especially when the formation of conjugated diaryl structures is possible. Examples of this type of reactions are the formation of stilbenes from phenyl coumarans or 1,2-diarylpropane struc-... 

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

Another useful approach to styrenes via sp -sp -coupling reactions, which is beyond the scope of this section, is Meerwein-type arylations in which aryldiazonium salts undergo usually copper(I)- or palladium-catalyzed couplings with electron deficient alkenes, indicating a radical-based mechanism.The method is so useful for the synthesis of stilbenes from unsubstituted styrenes 92 or p>silylstyrenes. 93... 

The stilbenes from the bark of Yucca periculosa F. Baker had growth regulatory activity against the Fall Army worm, an insect pest of com. 3,3, 5,5 -Tetrahydroxy-4-methoxystilbene was found to be the most active compound showing significant effect at 3 pg/g in diets. The results indicate the possible correlation of some antioxidant activities with insect growth and development [498],... 

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