Trans—1-alkyl—4-

Peralkylation of mesitylene w ilh 3 gave only reoriented products but no trans-alkylated products. It was found that the undesirable isomerization of 2,4.6-tris-(methyldichlorosilylethyl)mesitylene to the >,5,6- or 4..5,6-isomers could be avoided by carrying out the reaction in hexane solution at room temperature for 12 h. In this reaction, peralkylated product. 2.4.6-tris 2-(methyldichlorosilyl)-ethyllmesitylene, was obtained in 38% yield along with mono- and dialkylated mesitylene without any reoriented products in 7 and 37% yields, respectively. 

Au atom (see Fig. 15b). The high conductance values H represent an all-trans alkyl chain in combination with both sulfurs coordinated to two Au atoms in a bridge geometry (Fig. 15c). The theoretically predicted fourfold increase of the conductance, as compared to an atop-atop all-trans bridge, is close to the experimentally observed increase by a factor of 5. Other possible configurations with all-trans conformations (e.g., atop-bridge, multiple molecular junctions) are assumed to contribute as part of the distribution to the less-dominant peaks in the conductance histograms (e.g., M2, H2, and H3 in Fig. 13). 

Epal A process for making linear aliphatic alcohols by reacting ethylene with triethyl aluminum and oxidizing the products. Similar to Alfol, but incorporating a trans-alkylation stage that permits a wider range of products to be made. Developed by Ethyl Corporation (now Albermarle Corporation) and operated in the United States since 1964. 

Tsai, T.-C., liu, S.-B., and Wnag, I. (1999) Disproportionation and trans-alkylation of alkylbenzenes over zeolite catalysts. Appl Catal A, 181, 355-398. 

Tsai, T.S., and Wnag, I. (2002) Metal zeolite for trans-alkylation of toluene and heavy aromatics. Catal. Today, Ti, 39-47. 

Tsai, T.-C., Chao, P.-H., and Zeng, W.L (2007) Selective naphthene cracking over cascade dual catalyst in heavy aromatics trans-alkylation. Zeolite to Porous MOF Materials International Zeolite of Conference in Beijing, pp. 1611-1616. 

Alkylation with styrene gives 2,6-dialkyl TPB with a selectivity of 90% at 100% conversion. When the alkylation of TBP is completed, an excess of o-xylene is introduced into the reaction system, and 2,6-dialkylphenol is obtained through the trans alkylation without the need for separation of 2,6-dialkyl-4-/6r/-butylphenol (160) [Eq. (20)]. 

They have employed the strategy of intramolecular trans alkylation of azetidin-2-ones since C-4 substituted azetidin-2-one enolates, predominantly yield the C-3, 4-frans-diastereomer upon reaction with electrophiles, [45] thus, providing control of stereochemistry of substituents at the cyclohexyl ring (Scheme 25). 

Photochemical reaction of bifunctional ketoenamines in CC14 with maleic and fumaric acids and esters can be used for stereoselective synthesis of cis and trans alkyl 7-azabicyclo[2.2.1]heptanecarboxylates in good yield330 (equation 248). 

The anomalous products may be obtained by conversion of enamines 85 and 91 to the corresponding enolates 86 and 92 due to the effect of external base or the tetrasubstituted enamine, followed by attack on a second molecule of methyl vinyl ketone affording isomeric enolates 87 and 93. Protonation of these enolates would afford precursors to enones 88 (cis alkyl groups) and 94 (trans alkyl groups). 

Yields and product quality Both the alkylation and trans-alkylation reactions are highly selective—producing few byproducts. The EB product has high purity (99.9 wt% minimum) and is suitable for styrene-unit feed. Xylene make is less than 10 ppm. The process has an overall yield of 99.7%. 

Figure 6 Shape selective trans-alkylation of toluene to benzene and p-xylene.

Figure 7 Shape selective trans alkylation of m-xylene to 1,2,4-trimethylbenzene.

Considerable attention was given to the stereochemistry for the alkylation of metal enolates of y-butyrolactones during the past 1980 s decade. It is well recognized that electrophihc attack on the enolates of -substituted y-butyrolactones is controlled exclusively by the -substituent leading to the trans addition products . However, Iwasaki and coworkers reported the reverse diastereofacial differentiation in the alkylation of the enolates of a, S-dibenzyl-y-butyrolactones. These authors proposed that the factor controlling the selectivity in this case was allylic strain. Also, y-substituted y-lactones give stereoselective trans alkylation . ... 

Enolate (5)—4-Li was generated upon treatment of the heterocycle with lithium diisopropylamide (LDA) in THF solution and under a nitrogen atmosphere. The electrophile was then added at —78 °C to afford the trans-alkylated products with high diastere-oselectivity and in good yields (eq 6, Table 1). 

When the active center is located on the catalyst surface cis-trans conversion of the alkyl may be hindered due to the steric effect of the surface. This results in the stabilization of the active centers (complex F) which have the non-equivalence sites for monomer coordination and can be stereospecific centers, If the ligand environment of the active center permits rapid conversion of the cis-alkyl group (complex F) to the trans-alkyl (complex C) the coordination sites become equivalent in this case, the active center will be nonstereospecific. 

The different catalysts were extensively characterized. XPS indicated that the conventionally prepared sul ted zirconia catalysts contained sulfuric acid. The activity of the catalysts was determined with the gas-phase trans-alkylation of diethylbenzene with benzene and the solvent-free liquid-phase addition of acetic acid to camphene. 

The anhydrous bulk zirconium sulfate preparation did not display any activity in the trans-alkylation of benzene (1) and diethylbenzene (2) to ethylbenzene (3). At 473 K the silica-supported, gas-phase sulfated zirconia showed a very small activity, which rapidly dropped to a negligible level (Fig. 2). The conclusion is that Lewis acid sites are not active with sulfated zirconia catalysts. The low activity of the silica-supported catalyst is due to adsorption of some water leading to Bronsted acid sites. Desorption of water at 473 K leads to the decrease in activity with time. Pre-hydration of the supported catalyst brings about a slightly higher activity as apparent from Fig. 2 the activity drops again due to the loss of water. 

Fig. 3. Conversion of 2 in the trans-alkylation of benzene (1) and diethylbenzene (2) on H2S04/Zr02(prec.) (left-hand side) and on H2S04/Zr02(Gimex) (right-hand side) 473 K and 0 673 K.

In an extension of this method, Koenigs and Knorr subsequently reported that reaction between acylated glycosyl halides (bromides, chlorides, or iodides) with alcohols, in the presence of silver promoters (oxide or carbonate) furnished 1,2-trans alkyl glycosides. 

Yamamoto has also shown that the hydrogen is selectively removed from the trans alkyl group. " Ene reaction of (91) catalyzed by (93) gives (95) in 89% yield in 91% enantiomeric excess. Similar cycliza-tion of (92) gives (96) in 83% yield in 32% enantiomeric excess. The ene reactions of (85), (90), (91) and (92) indicate that rran.r-2-alkenylcyclohexanols are produced selectively in type I reactions (Scheme 16). 

Mixtures of CF3S03H and the triflates of B, A1 or Ga form a new superacid system, i.e. CF3S03H2 + [E(0S02CF3)4]- (E = B, A1 or Ga), which show superior catalytic activity in isomerization of alkanes, in trans-bromination and trans-alkylation of aromatics and in other related Friedel-Crafts reactions as compared with CF3S03H alone30-33. The relative reactivity sequence is B > Ga > Al. The triflates E(0S02CF3)3 were prepared from the reaction of EX3 (X = Br, Cl) with CF3S03H33. 

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