Methyl stilbene, trans

Cfs-butene should lead initially to the anti form trrms-butene should lead initially to the syn form and 1-butene should give rise initially to both. The equilibrium distribution of syn and anti forms usually differs greatly from the equilibrium distribution of cis- and frans-butene for cobalt complexes 59, 60) the syn form, precursor of irans-butene, is by far the most stable. By way of contrast for the corresponding carbanion, the cis anion seems by far the more stable. This preference for the cis carbanion is presumed to be the source of the high initial cis-to-trans ratio in the initial products of base catalyzed isomerization. In the base catalyzed isomerization of more complex cf-s-olefins (cfs-S-methyl-stilbene), the ions corresponding to syn and anti are not interconvertible and cis-trans isomeriza-... 

Starting Olefin trans-Stilbene trans-Stilbene °C acetone -78 acetophenone 0 1, 4-Trioxolane 3,3-dimethyl- 5-phenyl 3-methyl-3,5- diphenyl Formula C10H12O C15H14O ... 

Scheme 5 Enantioselective hydrogenation of trans-methyl stilbene 70 with PHOX-based Ir catalyst bearing different counterions...

Clear evidence that the geometry of the transition state is not constant has been provided by studies of eclipsing effects . Assuming anti stereospecificity, the threo and erythro isomers of the 1,2-diphenyl-l-propyl-X systems undergo bimolecular elimination to give the trans- and cw-a-methyl stilbenes respectively (75). 

Methyl 3-phenylpropionate 203-093-8 Methyl cinnamate 203-095-9 Benzyl isobutyrate 203-096-4 Di benzyl 203-098-5 Eccobrite RB Eccobrite RB-6 Stilbene trans-Stilbene Tinopal UNPA-GX 203-104-6 Ethyl cinnamate 203-105-1 Benzyl butyrate 203-106-7 Benzyl isovalerate 203-109-3 Benzyl cinnamate 203-113-5... 

Nucleophilic attack by a carbanion on a rhodium-acetylene complex has been postulated in the reaction of tolane with MeMgBr in the presence of (Ph3P)3 RhBr (Michman and Balog, 1971). This interpretation is supported by the known formation of rhodium-alkyne complexes under these conditions (Muller and Segnitz, 1973) and by the predominant formation of trans-a-methyl-stilbene. Additional study of the scope of this reaction would seem worthwhile since recycling of the rhodium-containing by-product (Ph3P)3 RhOH, should be possible. 

Although trans epoxides ean be obtained via epoxidation of aeyelie cti-eonjugated olefins under speeified eonditions, a direet method based on the epoxidation of trans-olefins would be valuable. The Katsuki group reeently identified eatalyst 15 as an effieient catalyst for the direet epoxidation of trans-olefins. Crucial to the sueeess of the eatalyst is the inherent adoption of a deeply folded eonformation eoupled with the use of ehlorobenzene as solvent. While only a limited number of substrates have been examined to date using catalyst 15, the results are very promising. For example, trans- -methyl styrene is epoxidized in 91% ee, trans-P-n-butyl styrene in 95% ee, and trans-stilbene in 87% ee. 

Die Reduktion von cis- und frarcs-a,/3-Diacetoxy-stilben in DMF/Tetrabutylammo-niumjodid an Quecksilber (-1,5 V vs. Ag/AgJ) fiihrt zu Tolan und bei —1,8 Volt zu trans-Stilben2. 2-Oxo-4-methyl-l,3-dioxolan wird an Graphit mit Lithiumperchlorat als Leitsalz unter C-O-Spaltung zu Propen reduziert3 ... 

If return occurs during the bromination of cw-stilbenes and rotation around the C-C bond is faster than collapse of the intermediates to dibromides, this process will lead to fra j-stilbene (Scheme 9). We used this test to check the possibility of return in the bromination of unsubstimted, 4-methyl, 4-trifluoromethyl-, and 4,4 -bis(trifluoromethyl)-stilbenes in DCE (ref. 24). All these olefins gave clean third-order rate constants spanning 7 powers of 10. For each cis-trans couple the cis olefin was brominated 3.5 to 5.5 times faster than the trans isomer. Reactions for products analysis were performed at initial molar ratios of Br2 to olefin of 1 to 2, so that products arose only from the cis olefin, the trans isomer being accumulated in the reaction medium. 

Chemically inert triplet quenchers e.g. trans-stilbene, anthracene, or pyrene, suppress the characteristic chemiluminescence of radical-ion recombination. When these quenchers are capable of fluorescence, as are anthracene and pyrene, the energy of the radical-ion recombination reaction is used for the excitation of the quencher fluorescence 15°). Trans-stilbene is a chemically inert 162> triplet quencher which is especially efficient where the energy of the first excited triplet state of a primary product is about 0.2 eV above that of trans-stilbene 163>. This condition is realized, for example, in the energy-deficient chemiluminescent system 10-methyl-phenothiazian radical cation and fluoranthene radical anion 164>. 

Up to about 10 percent of crs-stilbene was obtained when trimethyl-dioxetane 129 was decomposed in the presence of trans-stilbene 182) the electronic excitation energy of the excited carbonyl compounds formed in the cleavage of 129 (see Section V.) was transferred to trans-stilbene, so effecting the photochemical trans-cis isomerization. When bis (2.4-dinitrophenyl) oxalate reacted with hydrogen peroxide (see Section V. C. in the presence of o-tolyl-propane-1.2-dione 130, 2-methyl-2-... 

The same authors also reported the dispersion of palladium nanoparticles in a water/AOT/n-hexane microemulsion by hydrogen gas reduction of PdClJ and its efficiency for hydrogenation of alkenes in organic solvents [79]. UV-visible spectroscopy and TEM analysis revealed the formation of Pd nanoparticles with diameters in the range of 4 to 10 nm. Three olefins (1-phenyl-l-cyclohexene, methyl trans-cinnamate, and trans-stilbene) were used as substrates for the catalytic hydrogenation experiments under 1 atm of H2 (Table 9.12). All of the Start-... 

The treatment of the bromoacetal (255) with catalytic amounts ( 10%) of a Co(I) species, generated by the electroreduction of cobaloxime (232) in an Me0H-LiCl04 system at —1.8 V, produces the cis-fused adduct (256) in 60 70% yield (Scheme 96) [392]. Cathodic reduction is used for the synthesis of a [Co(CO)3PBu3] complex in a methanol-methyl formate medium, which catalyzes the alkoxycarbonylation of dichloromethane to dimethyl mal-onate in up to 75% yield [393]. The Co(II) complexes are found to be effective for the homogeneous reduction of gem-dichlorocyclopropanes in the presence of anthracene [394]. The formation of the C—C double bond of (258) may be ascribed to the a-elimination of the Co-H species. Thus, benzalchloride (257) can be converted to a mixture consisting primarily of ds- and trans-stilbenes (258) by the action of electrogenerated Co(I)(salen) (Scheme 97) [395-398]. 

Anthronylidene 64 forms no cycloaddition products with cis- or trans-4-methyl-2-pentene, but [1 -f-2]-cycloaddition is observed with stilbene derivatives. This is also attributed to the reacting triplet state I02,i30-i32) ... 

Kmeshy et al. [96], for the first time reported recyclable catalyst based on polymeric Cr(lll)(X) salen complexes derived from (lR,2R)-(-)-cyclohexanediamine with 5,5 -methylene di-3- erf-butylsalicylaldehyde and X = Cl, NO3, and CIO4 67-69 (Figure 22). These complexes were used in regio-, diastereo-, and enantioselective aminolytic kinetic resolution (AKR) of fra 5-stilbene oxide, trans- S- methyl styrene oxide, and 6-CN-chromene... 

FIGURE 10. Relative quantum yields for exciplex fluorescence (filled symbols) and addition product formation (open symbols) versus solvent dielectric constant for trans-stilbene with di isopropyl methyl amine (0)> ethyldiisopropylamine (A), and triethylamine ( ) in hexane-ethyl acetate and ethyl acetate-acetonitrile mixed solvents. From ref. (114) with permission of the American Chemical Society. 

An analogous cation radical chain process has been proposed for cis to trans isomerization of N-methyl-4-(6-stryl)-pyridinium ions via electron-transfer sensitization by Ru(bpy)-j2+ and metalloporphyrins (145). Quantum yields for isomerization are substantially higher in aqueous anionic micelles versus homogeneous solution due to the higher concentration of cis-styrylpyridinium ions. A radical cation chain mechanism may also account for previous reports of selective cis to trans sensitized photoisomerization of stilbene (25,26). 

On the other hand, the addition of a quaternary ammonium salt to the reaction medium accelerates the isomerization of the radical intermediate [36]. Thus, the epoxidation of c/j-stilbene in the presence of A -benzylquinine salt gives rranr-stilbene oxide with 90% ee as major product (Table 6B.1, entry 24). This protocol provides an effective method for the synthesis of trans-epoxides. In contrast to the epoxidation of c/s-di- and tri-substituted olefins for which complexes 11-13 are the catalysts of choice, the best catalyst for the epoxidation of tetra-substituted conjugated olefins varies with substrates (Table 6B.1, entries 27 and 28) [37]. The asymmetric epoxidation of 6-bromo-2,2,3,4-tetramethylchromene is well-promoted by complex 14 and that of 2-methyl-3-phenylindene, by complex 12a. 

Cavallo et al. from (+)-dihydrocarvone and evaluated in the asymmetric epoxida-tion of several silyl enol ethers [32]. Enantiomeric excess up to 74% was achieved in the epoxidation of the TBDMS trans-enol ether of desoxybenzoin with the fluoro ketone 19d (30 mol% of the ketone catalysts). In earlier work Solladie-Cavallo et al. had shown that the fluoro ketones 19a and 19e can be used to epoxidize trans-stilbene with up to 90% ee (30 mol% ketone catalyst) [33], Asymmetric epoxidation of trans-methyl 4-para-methoxycinnamate using ketone 19e as catalyst is discussed in Section 10.2. 

We acknowledge that although thermochemical estimates will occasionally be used in the current study, we forego the results from quantum chemical calculations largely in the name of brevity. We are forced to use benzalaniline (XIII), there being no enthalpy of formation known for its acyclic counterpart CH2=CH-CH=N-CH=CH2, for either of its isomers CH2=CH-CH=CH-CH=NH and CH2=CH-CH=CH-N=CH2, nor an unequivocal measured value for CH2=NH or any of its methylated derivatives (see the summaries of imine thermochemistry [21, 22]). We additionally note that benzalaniline, taken as its trans-isomer like its hydrocarbon counterpart stilbene (XII), is a conventional,... 

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