Stilbene aldehyde, trans

The effect of substrate structure on product profile is further illustrated by the reactions of cis- and trons-stilbene oxides 79 and 83 with lithium diethylamide (Scheme 5.17) [32]. Lithiated cis-stilbene oxide 80 rearranges to enolate 81, which gives ketone 82 after protic workup, whereas with lithiated trans-stilbene oxide 84, phenyl group migration results in enolate 85 and hence aldehyde 86 on workup. Triphenylethylene oxide 87 underwent efficient isomerization to ketone 90 [32]. 

Stilbenes that are used as fluorescent whitening agents are photolytically degraded by reactions involving cis-trans isomerization followed by hydration of the double bond, or oxidative fission of the double bond to yield aldehydes (Kramer et al. 1996). 

Shing and coworkers reported arabinose-derived uloses (59, 60) as epoxidation catalysts, and phenyl stilbene can be epoxidized by 60 in up to 90% ee (Fig. 20) [113-115]. In 2003, Zhao and coworkers reported aldehyde 61 to epoxidize trans-stilbene in up to 94% ee [116]. 

As stoich. [Ru(0)((N 0)p7CH3CN it oxidised primary alcohols to aldehydes, secondary alcohols to ketones, alkenes to aldehydes, tetrahydrofuran to y-butyrolactone. Styrene, cis- and tran -stilbenes gave benzaldehyde and adamantane gave 1-adamantol exclusively, while cyclohexanol gave cyclohexanone, suggesting that the complex is an effective oxidant for unactivated C-H bonds [636]. Immobilisation of the catalyst within Nation films on a basal plane pyrohtic graphite electrode was achieved, but the... 

As complex/aq. H O /CH Cl they epoxidised unfunctionalised alkenes RCH=CHj to a mixture of the epoxide and the aldehyde RCHO with e.e. values from 4% to 41%. Thus (Z)-2-methylstyrene gave the cw-epoxide with only traces of the trans-isomer [928, 929]. The reagent [RuCl(PNNP)]Vaq. H O /CH Cl epoxidised cis-stilbene, Z-2-methylstyrene and 1,2-dihydro-napthalene [844]. 

For epoxidations, electron-rich alkenes react more readily, in case of p-substituted styrenes, with a concomitant increase in the amount of aldehyde by-product, suggesting formation of an unsymmetric intermediate. However, cw-stilbene is converted to cis-stilbene oxide in 82% yield, and the intermediate, if any, must be short-lived. Under the same conditions, the reaction of trans-stilbene is slow. A close parallel approach of the double bond to the active heme site seems to be essential for epoxidation. 

The process development for this efficient Aggarwal-type sulfur-ylide epoxidation has recently been summarized in review [226], Several detailed studies of the reaction mechanism have also recently been reported [227-230]. In particular, a comprehensive experimental and computational investigation of the reaction mechanism has been performed by the Aggarwal group [227, 228]. The two dia-stereoselective pathways for synthesis of trans- and cis-stilbene oxides, as representative examples, are shown in Scheme 6.103 [228]. The initial step is addition of the sulfur ylide to the C=0 double bond of the aldehyde with formation of the cor-... 

Synthesis of OPV3 38 by the Horner-Wadsworth-Emmons reaction To a solution of aldehyde 6 (7.77 g, 40 mmol) and diphosphonate 37 (7.57 g, 20 mmol) in THF (200 mL) cooled in an ice-bath was added t-BuOK (4.94 g, 44 mmol) in small portions during 10 min. After stirring for 6 h at room temperature under a nitrogen atmosphere, the mixture was poured into H20 (300 mL). The yellow precipitate was filtered off, washed with H20 and dried. The product was dissolved in a minimum amount of boiling THF containing I2 (0.1 mM). The mixture was refluxed for 12 h and then slowly cooled to room temperature. The pure trans-stilbene 38 crystallized [10a]. 

Several ruthenium complexes bearing chiral Schiff s base ligands have been published. RuL(PPh3)(H20)2], complex C (Fig. 11), with PhIO produced (S)-styrene oxide in 80% ee [61]. Chiral Schiff s base complex D was examined using molecular oxygen with aldehyde, with or without 2,6-dichloropyridine N-oxide as an axial ligand. Styrene oxide was produced in up to 24% ee[62]. A chiral bis(oxazolinyl)pyridine ruthenium complex E with iodosylbenzene diacetate PhI(OAc)2 produced (lS,2S)-fra s-stilbene oxide in 74% ee [63]. Similarly, chiral ruthenium bis(bipyridine) sulfoxide complex F [64] was effective in combination with PhI(OAc)2 as an oxidant and resulted in in 33% ee for (R,R) trans-stilbene oxide and 94% ee for (R,R) trans-/i-Me-styrene (after 75 h at 25 °C). 

Periodic acid is a versatile oxidant since, depending on pH, the redox potential for the periodate-iodate couple varies from 0.7 V in aqueous basic media to 1.6 V in aqueous acidic media.Based on this observation, Villemin and Ricard devised an oxidative cleavage of glycols, in which mcjo-l,2-diphenyl-1,2-ethanediol was oxidized by periodic acid on alumina to benzaldehyde in 82% yield in aqueous ethanol (90% ethanol) at room temperature in 26 h. The same supported oxidant converted aromatics into quinones. In the presence of transition metal complexes (Mn ), a-arylalkenes suffer oxidative cleavage to aldehydes. For example, tran.r-stilbene gives benzaldehyde at room temperature. 

In Figure 3 it is seen that, if a trans-stilhene solution containing benzaldehyde (spectrum I) is ozonized, the CO band due to the aldehyde at 1706 cm. i does not disappear but becomes much stronger (spectrum II). Therefore, a material with a CO band must have been produced which shows the same frequency as that of the aldehyde. Thus a protective action of the double bond against the autoxidation accelerated by ozone is plainly manifest. In the latest measurements it has been found that the stilbene double bond protects benzaldehyde against autoxidation due to oxygen alone thus substances with a double bond may act also as antioxidants. 

Dihydroxylation of the stilbene double bond in the trans isomers of Combretastatin A-1 and A-4 produced diols which by treatment with boron trifluoride in ethyl ether [44] or with trifluoroacetic acid [17] resulted in pinacolic rearrangement to produce an aldehyde. The aldehyde was converted in a variety of derivatives, as illustrated in the Scheme 20, via the following reaction sequence reduction with sodium borohydride to primary alcohol which was derivatized to the corresponding mesylate or tosylate, substitution with sodium azide and final reduction to amine with lithium aluminum hydride. Alternatively the aldehyde was converted to oxime which was catalitically hydrogenated to amine [17]. 

The stilbene obtained from the salt (73) and the aldehyde (74) in methanol was predominantly trans whereas it was predominantly cis when the reaction was carried out in DMF. ... 

The generation of carbenes from tosylhydrazones of thiophene aldehydes, and their reactivity have been discussed in CHEC-I, <84CHEC-I(4)74i>. A few further reactions of such carbenes have been reported. In presence of acrylonitrile, the product could be either the cyclopropane (484) (from the carbene) or the pyrazoline (485) (by cycloaddition of the diazo intermediate) <88H(27)ll4i>. The carbene can similarly be trapped by cis and trans stilbene, dimethyl fumarate or maleate to form the respective cyclopropanes <87BCJ4317>. 

The sodium diethyl phosphite reacts with aromatic aldehydes yielding tran -stilbene-type compounds [380]. 

Ester- and nitrile-stabilized ylid anions are more reactive than the corresponding neutral ylids and react with ketones (even enolizable ones) as well as aldehydes. E a,p- thylenecarboxylic acid esters. 2 eqs. BuLi (in hexane) added to a stirred suspension of startg. diphenylphosphonium bromide in THF, 1 eq. acetone added, and stirring continued at room temp, for 30 min product. Y 43% (Y 10% using 1 eq. BuLi and 0% with PhjP = CHC02Me). F.e. incl. a,p-ethylenenitriles, and trans stereo-selectivity with aldehydes, s. E.G. McKenna, B.J. Walker, J. Chem. Soc. Chem. Commun. 1989, 568-9 (E)-stilbene s. Tetrahedron Letters 29, 485-8 (1988). 

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