Addition catalyzed

Whereas sulfolane is relatively stable to about 220°C, above that temperature it starts to break down, presumably to sulfur dioxide and a polymeric material. Sulfolane, also stable in the presence of various chemical substances as shown in Table 2 (2), is relatively inert except toward sulfur and aluminum chloride. Despite this relative chemical inertness, sulfolane does undergo certain reactions, for example, halogenations, ting cleavage by alkah metals, ring additions catalyzed by alkah metals, reaction with Grignard reagents, and formation of weak chemical complexes. 

Ring Additions Catalyzed by Alkali Metals. The addition of tributyltin chloride and olefins such as styrene, isoprene, or butadiene to sulfolane is cataly2ed by alkah metals, including sodium and lithium, and by sodium amide (10—13). The addition of tributyltin chloride to sulfolane in the... 

The kinetic principles operating during the initiation and advance of interface-controlled reactions are identical with the behaviour discussed for the decomposition of a single solid (Chaps. 3 and 4). The condition that overall rate control is determined by an interface process is that a chemical step within this zone is slow compared with the rate of arrival of the second reactant. This condition is not usually satisfied during reaction between solids where the product is formed at the contact of a barrier layer with a reactant. Particular systems that satisfy the specialized requirements can, however, be envisaged for example, rate processes in which all products are volatilized or a solid additive catalyzes the decomposition of a solid yielding no solid residue. Even here, however, the kinetic characteristics are likely to be influenced by changing effectiveness of contact as reaction proceeds, or the deactivation of the catalyst surface. 

Figure 3.5 Michael addition catalyzed by the SerlOSAla C. antarctica lipase B mutant.

R. S. E. Conn, A. V. Lovell, S. Karady, L. M. Weinstock, Chiral Michael Addition Methyl Vinyl Ketone Addition Catalyzed by Cinchona Alkaloid Derivatives , J. Org Chem. 1986, 51, 4710-4711. 

Figure 18. Stereochemical model for conjugate additions catalyzed by arenethiolato—copper complexes. [Adapted from (145, 146).]...

Scheme 34 Michael additions catalyzed by one-, two- or threefoldly reduced fullerene.

Espelt, L., Parella, T., Bujons, J., Solans, C., Joglar, J., Delgado, A. and, Clapes, P., Stereoselective aldol additions catalyzed hy dihydroxyacetone phosphate-dependent aldolases in emulsion systems preparation and structural characterization of linear and cyclic iminopolyols from aminoaldehydes. Chem. Eur. J., 2003, 9, 4887. 

This pyridoxal-phosphate-dependent enzyme [EC 2.1.2.5], also known as glutamate formyltransferase, catalyzes the reaction of 5-formiminotetrahydrofolate with L-glutamate to produce tetrahydrofolate and A-formim-ino-L-glutamate. The enzyme will additionally catalyze the transfer of the formyl moiety from 5-formyltetrahy-drofolate to L-glutamate. This protein occurs in eukaryotes as a bifunctional enzyme also having a formiminote-trahydrofolate cyclodeaminase activity [EC 4.3.1.4]. 

Scheme 3.2 Asymmetric conjugate addition catalyzed by chiral phosphine-rhodium complexes [7-11].

Scheme 3.6 Catalytic cycle for the conjugate addition catalyzed by a rhodium-acetylacetonato complex [16].

I 3 Rhodiumllj-Catalyzed Asymmetric Addition of Organometallic Reagents to Electron-Deficient Olefns Tab.3.2 Asymmetric conjugate addition catalyzed by [Rh(OH)((S)-BINAP)]2 [15],... 

Scheme 3.7 Stereochemical pathway in the conjugate addition catalyzed by the rhodium-(S)-BINAP complex [6, 20, 25].

Maddaford reported the diastereoselective synthesis of C-glycosides 29 using conjugate addition catalyzed by cationic rhodium catalysts such as [Rh(COD)2]BF4 (Eq. 1) [24]. Addition of phosphine hgands to the reaction system inhibited the conjugate addition. It is likely that the enone 28 derived from the pyranose is less reactive toward the conjugate addition. 

Here, we will focus on the enzymatic routes since enzymatic preparation of DHAP is usually coupled with the aldol addition catalyzed by the aldolase representing genuine multi-enzyme systems. 

Rare or unnatural monosaccharides have many useful applications as nonnutritive sweeteners, glycosidase inhibitors and so on. For example, L-glucose and L-fructose are known to be low-calorie sweeteners. In addition, rare or unnatural monosaccharides are potentially useful as chiral building blocks for the synthesis of biologically active compounds. Therefore, these compounds have been important targets for the development of enzymatic synthesis based in the use of DHAP-dependent aldolases alone or in combination with isomerases. Fessner et al. showed that rare ketose-1-phosphates could be reached not only by aldol addition catalyzed by DHAP-dependent aldolases, but by enzymatic isomerization/ phosphorylation of aldoses [35]. Thus, for example, L-fructose can be prepared... 

The best chemical and optical yields in the above reactions are obtained by using (S)- or (R)-proline. Some 19-norsteroids are prepared on an industrial scale from products of intramolecular aldol additions catalyzed by (S)-proline 68). 

To obtain a useful fuel cell, polarization must therefore be kept as slight as possible. This can be done by choosing an electrolyte of good conductivity and above all by accelerating the electrode reactions. In low-temperature cells, that operate with aqueous electrolytes the reactions at both cathode and anode can be considerably accelerated by the addition of very active catalysts. These materials are incorporated in the appropriate electrode, so that the electrode not only conducts the current but in addition catalyzes the reaction. The rest of this paper is devoted exclusively to cells of this type. 

Other authors have described the lipase-catalyzed chemoselective acylation of alcohols in the presence of phenolic moities [14], the protease-catalyzed acylation of the 17-amino moiety of an estradiol derivative [15], the chemoselectivity in the aminolysis reaction of methyl acrylate (amide formation vs the favored Michael addition) catalyzed by Candida antarctica lipase (Novozym 435) [16], and the lipase preference for the O-esterification in the presence of thiol moieties, as, for instance, in 2-mercaptoethanol and dithiotreitol [17]. This last finding was recently exploited for the synthesis of thiol end-functionalized polyesters by enzymatic polymerization of e-caprolactone initiated by 2-mercaptoethanol (Figure 6.2)... 

Related studies have recently been reported by the same author on propargyl steres reactions with dicarbonyl compounds or electron-rich arenes [135], to provide an atom-economical functionalization of carbon nucleophiles under catalytic conditions, using a very different method of addition catalyzed by Lewis acids [136]. 

A variety of 1,6-diyne substrates have been investigated for activity in the HSiR3/CO system. A ruthenium complex, Ru3(CO)12, with a tertiary phosphine additive catalyzes the formation of good yields of catechol products in which one molecule of diyne, two molecules of CO, and one or two molecules of silane are incorporated, as seen in Eq. (39).108... 

Scheme 9.—The Reversible Addition Catalyzed by Sialyl Aldolase.

Spirocyclization of amines. Two new syntheses of desamylhistrionicotoxin (1) involve as the key reactions a Michael addition catalyzed by (CH3)3SiI (equation I) and a spirocyclization of an allylic alcohol amine catalyzed by (CH3)3SiI (equation... 

Addition of water to the double bond of the hydroxy-D-glucal would produce D-glucose. Although such addition, catalyzed by sulfuric acid,... 

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