Molecular sieves substituted

The reaction of a halide with 2-butene-1,4-diol (104) affords the aldehyde 105, which is converted into the 4-substituted 2-hydroxytetrahydrofuran 106, and oxidized to the 3-aryl-7-butyrolactone 107[94], Asymmetric arylation of the cyclic acetal 108 with phenyl triflate[95] using Pd-BINAP afforded 109, which was converted into the 3-phenyllactone 110 in 72% ee[96]. Addition of a molecular sieve (MS3A) shows a favorable effect on this arylation. The reaction of the 3-siloxycyclopentene 111 with an alkenyl iodide affords the. silyl... 

The method outUned above was initially investigated for the introduction of isolated Ti(IV) sites onto a sihca substrate for use in selective oxidation catalysis. Since the development of a silica-supported Ti(lV) epoxida-tion catalyst by Shell in the 1970s, titania-sihca materials have attracted considerable attention [135,136]. Many other titania-sihca materials have been studied in this context including, but not hmited to, TSl and TS2 (titanium-substituted molecular sieves), Ti-/i (titanium-substituted zeolite). 

For example, direct fluorinations with elemental fluorine are kept imder control in this way, at very low conversion and by entrapping the molecules in a molecular-sieve reactor. As with some other aromatic substitutions they can proceed by either radical or electrophilic paths, if not even more mechanisms. The products are dif ferent then this may involve position isomerism, arising from different substitution patterns, when the aromatic core already has a primary substituent further, there may be changed selectivity for imdefined addition and polymeric side products (Figure 1.31). It is justified to term this and other similar reactions new , as the reaction follows new elemental paths and creates new products or at least new... 

An extremely versatile catalyst for a variety of synthetically useful oxidations with aqueous hydrogen peroxide is obtained by isomorphous substitution of Si by Ti in molecular sieve materials such as silicalite (the all-silica analogue of zeolite ZSM-5) and zeolite beta. Titanium(IV) silicalite (TS-1), developed by Enichem (Notari, 1988), was the progenitor of this class of materials, which have become known as redox molecular sieves (Arends et al., 1997). 

ESEEM measurements of perdeuterated all-trany-p-carotene imbedded in activated Cu-substituted MCM-41 molecular sieve revealed (Gao et al. 2005) that two deuterons of the carotenoid interact with the Cu2+ at a distance of 3.3 A. Possible double bonds of P-carotene with one deuterium at each carbon that could interact with Cu are C7=C8, CH-C12, 05=05, 02 - C1T, and C8 =C7. 

Lawrence, J., A. L. Focsan et al. (2008). Pulsed ENDOR studies of carotenoid oxidation in Cu(II)-substituted MCM-41 molecular sieves. J. Phys. Chem. B 112 1806-1819. 

Prakash, A. M., H. M. Sung-Suh et al. (1998). Electron spin resonance evidence for isomorphous substitution of titanium into titanosilicate TiMCM-41 mesoporous molecular sieve. J. Phys. Chem. B 102 857-864. 

Hasegawa and co-workers illustrated the syntheses of substituted phenazine-5,10-dioxides 236 by a dehydrative condensation between benzofuroxan 234 and dihydroxybenzene derivatives 235 catalyzed by molecular sieves at room temperature <00H2151>. 

Narasaka et al.16 reported that 53 catalyzes Diels-Alder reactions of 54-type substrates with diene in the presence of 4 A molecular sieves (Scheme 5-18). A remarkable solvent effect on the enantioselectivity is observed. High enantio-selectivity is attained using mesitylene as the solvent. As shown in Scheme 5-18, the reaction of 54a with isoprene proceeds smoothly in this solvent, affording product 55a with 92% ee. Other 3-(3-substituted acryloyl)-l,3-oxazolidin-2-ones 54b-d also give good results (75-91% ee) when reacted with cyclopentadiene. 

These structures are unique for several reasons. First, they represent three new multidimensional 12-MR systems, which are rare even among zeolites. Second, the amount of framework substitution by metals such as Mn2+ and Mg2+ was unknown prior to this series. Also, the ease of forming both gallium and aluminum phosphates appear to be comparable. Finally, it would appear the charge-matching approach has proven to be a successful strategy for the synthesis of new molecular sieves. It is not clear whether these materials are thermally or hydrothermally stable but they do represent novel pore structures that should impart some unusual properties. 

The catalyst was prepared from the corresponding chiral diol and TiCl2(OPr-/)2 at room temperature in the presence of 4 A molecular sieves. Without molecular sieves, stoichiometric amounts of the titanium complex were required to obtain an equally high enantioselectivity. A remarkable solvent effect was observed. Various cycloadducts were only obtained with high optical yields when non-polar solvents were employed252,253. For example, 4-substituted 4-cyclohexene-1,2-dicarboxylate derivatives 408 were obtained with ee values ranging from 91 to 94% in the reactions of 91a, 399 and 407 with 17b in toluene/... 

Titanosilicates molecular sieves, especially TS-1, have been widely studied for the selective oxidation of a variety of organic substrates, using aqueous H202. ° Recently, there have been attempts to substitute aqueous H2O2 by a mixture of H2 and O2 in the presence of metals such as Pd, Pt, Au, etc. Selectivities of 99% for propylene oxide formation from propylene were observed by Haruta and co-workers over Au-containing catalysts. We had also found that the epoxide selectivity in the epoxidation... 

Most of the catalytic interest in the AlP04-based molecular sieves have centered on the SAPOs which have weak to moderate Bronsted acidity, and two have been commerciahzed SAPO-11 in lube oil dewaxing by Ghevron and SAPO-34 in methanol-to-olefins conversion by UOP/Norsk Hydro. Spurred on by the success of TS-1 in oxidation catalysis, there is renewed interest in Ti, Co, V, Mn and Cr substituted AlP04-based materials, for a review of recent developments in the AlP04-based molecular sieves see [35]. 

Flanigen, E.M. and Grose, R.W. (1971) Phosphorus substitution in zeolite frameworks. Adv. Chem. Ser., 101 (Molecular Sieve Zeolites-I), 76-101. 

Figure 22 Mechanism of 2-propanol oxygenation in an iron-substituted aluminophos-phate molecular sieve.

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