Dimethoxy stilbene

Fig. 28 Derivative cyclic voltammograms for the oxidation of 4,4 -dimethoxy-stilbene in acetonitrile at 25°C (a) and — 30°C (b). Voltage sweep rate = 100 V s". (BU4NBF4) = 0.1 M. (Aalstad et al., 1981a)...

S Ljunggren, E Johansson. The kinetics of hgnin reactions during oxygen bleaching. Part 2. The reactivity of 4,4 -dihydroxy-3,3 -dimethoxy-stilbene and (3-aryl ether structures. Nordic Pulp Pap Res / 5 148-154, 1990. 

Laudanosine contains four methoxyl groups. By exhaustive methyla-tion it yields trimethylamine and laudanosene (tetramethoxy-o-vinyl-stilbene), CH2=CH—C6H2(OCH3)2—CH=CH—C6H3(OCH3),. On oxidation with manganese dioxide and sulphuric acid it furnishes, in addition to the interesting by-product 2 3 6 7-tetramethoxy-9 10-dihydroanthracene, veratraldehyde and 4 5-dimethoxy-2 )3-methyl-... 

Intermediates generated at an electrode surface may react while still near the electrode. If so, one side of the intermediate may be wholly or partly shielded from attack by other reactants by the electrode itself. Such behavior is particularly common in the electrochemical oxidation of aromatic compounds since, as we have already seen with coumarin, aromatic compounds are generally tightly adsorbed parallel to the electrode surface at potentials positive of the p.z.c. For example, electrochemical oxidation of the stilbenes in alkaline methanol affords a mixture of dl and meso-1,2 dimethoxy-1,2-diphenylethane (1) 10>. It is found that c/s-stilbene affords a mixture of isomers of 1 in which the... 

Cohare and co-workers reported that aristolactam BU (22) was prepared, following Kupchen s method, by Perkin condensation of 6-bromo-3,4-di-methoxy phenyl acetic acid (119) and o-nitrobenzaldehyde (120) (Scheme 14). The 2-bromo-4,5-dimethoxy-2 -nitro-ds-stilbene-a-carboxylic acid (121) was obtained. The nitro group of 121 was reduced with ferrous sulfate and ammonium hydroxide, and the resulting 2-bromo-4,5-dimethoxy-2 -amino-cw-stilbene-a-carboxylic acid (122) without purification was submitted to the Pschorr phenanthrene synthesis to yield l-bromo-3,4-dimethoxyphen-anthrene-lO-carboxylic acid (123). The phenanthrylamine 124 was prepared from 123 via a Schmidt reaction, and, by treatment with n-butyllithium and CO2, 124, afforded 22 (42). 

The postulation that the structure of one dimer is 2,4 -dihydroxy-3,3 -dimethoxy-5-ethylbibenzyl is, of course, based on NMR data, on the proposal that phenylcoumarane structures are common in lignin [see (/)], and on evidence that they are cleaved to stilbenes by alkali (14) and eliminate 7-methylol units (2) as formaldehyde by mechanisms quite analogous to those above. Although there are some modest surprises in the structure of dimers isolated so far, it is gratifying how well these results fit into our long-standing concepts of lignin structure and reactions. 

SYNS (trans)-2,5-DIMETHOXY-4 -AMINOSTILBENE 4-(2,5-DIMETHOXYPHENETHYL)ANILINE 4-(2-(2,5-DIMETHOXYPHENYL)ETHYL)BENZENAMINE 4-(2,5-DIMETHOXY)STILBENAi nNE 2,5-DIMETHOXY-4 -STILBEN AMINE... 

Fig. (4). A combination of 3,4-methylenedioxy-5,4 -dimethoxy-3 -amino-( -stilbene with the des-Doe tetrapeptide unit of the tubulin assembly inhibitor dolastatin 10...

The retrosynthesis of Aara-e-viniferin (445) by Thomas et al. indicated that the y-butyrolactone (823) was a key intermediate, which later converted from the corresponding stilbene by manganese triacetate-mediated oxidative lactonization (Scheme 18) [407]. In subsequent papers, they described the FeCb-promoted tandem pericyclic synthesis of catechol analogs of restrytisol C. 3,4-Dimethoxy-12-acetoxy stilbene (824), which was synthesized by Heck coupling, was treated with FeCb to give the unnatural stilbene dimers 585 and 586 (Scheme 19) [288]. 

Treatment of 3,4-dimethoxy-12-benzyloxymethyl stilbene under the same condition gave catechol analogs of ampelopsin F and of restrytisol C (587, 588) [289]. 

Proof of the structure [xi] was sought and found by the oxidation of phenyldihydrothebaine with alkaline potassium permanganate, which resulted in the production of benzaldehyde, benzoic acid, and 4-methoxyphthalic acid. By exhaustive methylation of the methyl ether the optically active (+)-3 4-dimethoxy-2-(5-methoxy-2-vinylphenyl) stilbene [xn] (prepared by Freund [1], but stated to be optically inactive) was obtained, and permanganate oxidation of this afforded 5 6 5 -trimethoxydiphenaldehyde [xm] (also obtained by the ozonoly-sis of [xn]) and 5 6 5 -trimethoxydiphenic acid [xrv] (also obtained by oxidation of [xm]). This acid was identified with an authentic specimen prepared in stages from 4-acetoxy-3 6-dimethoxyphenanthrene quinone (acetylthebaolquinone [xv]) [6-7, 9-10],... 

Unsaturated Lignin Model Compounds Double bonds in lignin model compounds are attacked by peracetate ions. Dehydro-di-woeugenol (XXI, Figure 12.9) reacted with epoxidation of the aliphatic double bond and formation of the diol. The double bonds in stilbenes [59] and coniferaldehyde [90] are also cleaved. FemUc acid (IVa) and its ethyl ester reacted slowly at 50°C the methyl ether, 3,4-dimethoxy cinnamic acid, was much less reactive and was almost quantitatively recovered [55]. The reactions of ferulic acid and its ethyl ester (both in the trans form) were accompanied by trans-cis isomerization, perhaps an indication of reversible phenoxy radical formation. HomovanilUc acid (XXXa) was also formed the proposed mechanism involved epoxidation of the a-P double bonds followed by decarboxylation. 

Bei der Belichtung von 4-Methoxycarbonylamino-2, 5 -dimethoxy-trans-stilben (IV) entstehen die beiden Dimeren V und VI in vergleichbaren Mengen. Die Quantenausbeute der Dimerisierung (A = 365/366 nm 0,03 m Losung in Benzol) betragt

[Pg.330]

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