Methoxy-substituted stilbenes

Both these parameters reflect a moderate stability for BrN3 in methanol. This feature made it impossible to apply the azide clock method to determine the lifetime of the ionic intermediates arising from deactivated alkenes (for example, / ,p -bis(trifluoromethyl)stilbenes). Nevertheless, for a couple of p-methoxy substituted stilbenes and unsubstituted stilbenes the selectivity ratios reported in Table II have been found. (IT)... 

The a-P double bond in hydroxy- or methoxy-substituted stilbenes should also be stable to hydroperoxide ion. It is the electron withdrawing carbonyl group in cinnamaldehydes that makes their double bond susceptible to nucleophilic attack. 

A paper by Gierer et al. [63] probably resolves the mechanism. These workers found that a number of hydroxy- or methoxy-substituted stilbenes would react with hydroxyl radicals, or with a combination of superoxide and hydroxyl radicals. The formation of superoxide and hydroxyl radicals by hydrogen peroxide decomposition is hard to prevent and incomplete chelation of metal ions might explain the inconsistent results reported by the earlier workers. 

The fluorescence of trans-stilbene and four methoxy-substituted stilbene derivatives... 

The first commercial carbocyclic products were derivatives of 4,4 -diaminostil-bene-2,2 -disulfonic acid, e.g., 4,4 -bis(phenylureido)stilbene-2,2 -disulfonic acid disodium salt [2606-93-1] [26] and acylamino- or methoxy-substituted benzoyla-mino derivatives [6], Because of their poor efficiency (i.e., yield of whiteness) and hue, these products have disappeared from the market. 

C.F. Bernasconi et al.. Kinetics of the Reaction of p-Methoxy-a-stilbene with Thiolate Ions - 1st Direct Observation of the Intermediate in a Nucleophilic Vinylic Substitution, J. Am. Chem. Soc., 1984,111,6862. 

The fluorescence of Irons-stilbene and four methoxy-substituted stUbene derivatives has been detected in a variety of solvents [37]. Compared to other stUbene derivatives, trons-3,5-dimethoxystilbene displayed a large quantum yield of fluorescence and a low quantum yield of trans-cis isomerization in polar organic solvents. 

The synthesis of other biologically active thiazoles was described by Ohsumi et al. [50] and is shown in Scheme 16. Condensation of phosphonium bromide and 4-methoxy-3-nitrobenzaldehyde gave a 1 1 mixture of (Z)- and (-E)-stilbenes. ( )-stilbene 64 was purified by crystallization and then converted to bromohydrin 65 by NBS-H2O. Oxidation of the bromohydrin by DMSO-TFAA gave the bromoketone intermediate 66, which was condensed with thiocarbamoyl compounds in the presence of Na2C03 in DMF to give the corresponding 2-substituted thiazole derivatives (67a and b). Compound 67a... 

Such reactions have also been carried out on benzofurans carrying benzyl, fluoro, chloro, bromo, methoxy, cyano, and phenyl groups in the benzo ring. Substitution in the stilbene part of the molecule can also be obtained by the use of Schiff s bases derived from differing benzal-dehydes.26,28,29... 

Derivatives have also been obtained in which the 1,2,3-triazole ring is substituted by chlorine83 and/or methoxy groups,66 as, for example, in the formation of the stilbene 148 from 2-(jP-tolyl)-5,7-dimethyl-benzoxazole (146) and Schiff s base 147. 

Of particular interest are cases in which substituents are present in ortho positions to the reacting methyl group. Apart from o-chloro-substituted derivatives, those with methoxy, carbonamido, sulfonamido, and phenylsulfonyl groups have been reported to undergo reaction.68 The 2-(3-chloro-4 methyIphenyl)-5-methoxybenzotriazole (163) has been found to be particularly reactive, yielding, with Schiff s base 98, the stilbene 164.54... 

The p for stilbene derivatives are much higher than their benzene analogs (JL). To determine the effect of substitution on the nonlinearity, 4-methoxy-41-nitrostilbene... 

Condensations of aryiacetic acids, arylacetates and arylacetonitriles with aromatic aldehydes and ketones proceed under standard Knoevenagel conditions, providing access to stilbenes or substituted stil-benes. - Thus 3-nitrobenzaldehyde and 4-nitrophenylacetic acid react in the presence of different amines to give (130), (131) and (132). The ratio of the products varies greatly with the amine used. (131) and (132) could easily be transformed into (130) in high yield. Reaction of arylacetates with o-hydroxybenzaldehydes yields the corresponding coumarins. The condensation of 2-hydroxy-4-meth-oxybenzaldehyde (133) with pyridylacetates like (134) yields 7-methoxy-3-pyridylcoumarins like (135) (Scheme 20). 

Interest has been shown in the oxides of dicyclopentadiene, as noted earlier, with reports of epoxidations using permaleic, perphthalic, " and peracetic acids. The mechanism of oxidation of fran -stilbene by peroxomonophosphoric acid (H3PO5) in a number of solvents has been investigated. A report on the epoxidation of a number of methoxy- and hydroxy-substituted cinnamaldehydes (24 R = = H, MeO, or OH) concludes with the suggestion that the... 

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