Catalysts containing lithium

A) in Scheme l).9 Furthermore, asymmetric Diels-Alder reactions have been developed in LPDE solutions or using hetero-bimetallic catalysts containing lithium ions (compound... 

A remarkable process was reported by Mori that forms aniline from dinitrogen (Equation (26)).106 Titanium nitrogen fixation complexes were generated from reactions of titanium tetrachloride or tetraisopropoxide, lithium metal, TMS chloride, and dinitrogen. These complexes generated a mixture of aryl and diarylamines in yields as high as 80% when treated with aryl halide and a palladium catalyst containing DPPF ... 

Reactions of allylic electrophiles with stabilized carbon nucleophiles were shown by Helmchen and coworkers to occur in the presence of iridium-phosphoramidite catalysts containing LI (Scheme 10) [66,69], but alkylations of linear allylic acetates with salts of dimethylmalonate occurred with variable yield, branched-to-linear selectivity, and enantioselectivity. Although selectivities were improved by the addition of lithium chloride, enantioselectivities still ranged from 82-94%, and branched selectivities from 55-91%. Reactions catalyzed by complexes of phosphoramidite ligands derived from primary amines resulted in the formation of alkylation products with higher branched-to-linear ratios but lower enantioselectivities. These selectivities were improved by the development of metalacyclic iridium catalysts discussed in the next section and salt-free reaction conditions described later in this chapter. 

Triple bonds in side chains of aromatics can be reduced to double bonds or completely saturated. The outcome of such reductions depends on the structure of the acetylene and on the method of reduction. If the triple bond is not conjugated with the benzene ring it can be handled in the same way as in aliphatic acetylenes. In addition, electrochemical reduction in a solution of lithium chloride in methylamine has been used for partial reduction to alkenes trans isomers, where applicable) in 40-51% yields (with 2,5-dihydroaromatic alkenes as by-products) [379]. Aromatic acetylenes with triple bonds conjugated with benzene rings can be hydrogenated over Raney nickel to cis olefins [356], or to alkyl aromatics over rhenium sulfide catalyst [54]. Electroreduction in methylamine containing lithium chloride gives 80% yields of alkyl aromatics [379]. 

In the Mukaiyama aldol additions of trimethyl-(l-phenyl-propenyloxy)-silane to give benzaldehyde and cinnamaldehyde catalyzed by 7 mol% supported scandium catalyst, a 1 1 mixture of diastereomers was obtained. Again, the dendritic catalyst could be recycled easily without any loss in performance. The scandium cross-linked dendritic material appeared to be an efficient catalyst for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene. The Diels-Alder adduct was formed in dichloromethane at 0°C in 79% yield with an endo/exo ratio of 85 15. The material was also used as a Friedel-Crafts acylation catalyst (contain-ing7mol% scandium) for the formation of / -methoxyacetophenone (in a 73% yield) from anisole, acetic acid anhydride, and lithium perchlorate at 50°C in nitromethane. 

For reasons of space diolefin polymerization has not been included in this Chapter. Some information and pertinent references are summarized here. 1,3-E>ienes can be polymerized by lithium alkyls or by Ziegler-Natta type catalysts, containing titanium or cobalt, nickel, and neodymium. Industrially important products are 1,4-cis-polybutadiene (>2 Mt/a) and 1,4-cis-polyisoprene (>1 Mt/a). They are... 

Some catalysts contain oxides of lithium, beryllium and vanadium as promoters. 

Additionally, if the initiation reaction is more rapid an the chain propagation, a very narrow molecular weight distribution, MJM = 1 (Poisson distribution), is obtained. Typically living character is shown by the anionic polymerization of butadiene and isoprene with the lithium alkyls [77, 78], but it has been found also in butadiene polymerization with allylneodymium compounds [49] and Ziegler-Natta catalysts containing titanium iodide [77]. On the other hand, the chain growth can be terminated by a chain transfer reaction with the monomer via /0-hydride elimination, as has already been mentioned above for the allylcobalt complex-catalyzed 1,2-polymerization of butadiene. 

Hydrogenation of C02 occurs on a number of solid catalysts with Cu0/Zn0/Al203, methanol can be prepared but the equilibrium yields are less than 40%. The use of hybrid catalysts, containing solid acids, improves the yields by partial dehydration of the methanol to dimethyl ether.56 In situ IR spectroscopy has been used to identify catalytic intermediates in some processes. With Cu/ZrO/Si02, surface bound formate, gem-diolate and methoxide species could be observed before the final hydrolysis to methanol.57 Lithium salt-promoted Rh/Si02 catalysts increased the ethanol content of reduction mixtures from C02 as compared to the unpromoted reactions, but the main product was methane.58... 

Ketones. Although Ni-catalyzed cychzation of iodoaryl-containing lithium enolates shown in Scheme might represent the first example of this class of reactions, subsequent studies have been performed mainly with Pd catalysts. The syntheses of spiro-fused oligocyclic models for fredericamycin A by Ciufolini and co-workers provided some prototypical examples of Pd-catalyzed cycUzalion via intramolecular a-arylation of ketones (Scheme 20). Under appropriate conditions, bromoaryl-containing monoketones can also be converted to spiro-fused bicycles and oligocycles (Scheme 20). 

P-Pinene, a byproduct of the wood and paper industry, is the starting material for an enantioselective synthesis of (i )-citronellal Thermal cycloreversion leads to myrcene. The allylamine obtained by lithiation of myrcene with butyllithium and diethylamine involving an intermediate lithium chelate rearranges stereoselectively in the presence of a chiral catalyst containing the BlNAP-ligand (2,2 -bis-(di-phenylphosphino)-l,r-binapthyl = BINAP) (telomerization) to the enamine, which then readily undergoes acid-catalyzed hydrolysis to (7 )-(+)-citronellal with high enantiomeric excess. 

Iwata et al. also established the direct catalytic asymmetric aldol reaction of thioamides (Scheme 8.39)." Treatment of an aldehyde and thioamide 259 in the presence of the catalyst containing [Cu(MeCN)4]BF4, (7 ,/ )-Ph-BPE, and lithium phenoxide 260 gave (3-hydroxythioamide 261 in good yield with high stereoselectivity. Thioamide features the direct transformation into aldehyde by using a Schwarz reagent (Scheme 8.40)." They converted aldol adduct 261 into (3-siloxyal-dehyde 262, which was further submitted to the direct stereoselective aldol reaction. Both diastereomers 263 and 264 were obtained in good yield. This protocol is effective to synthesize sequential 1,3-polyols. 

Common catalyst compositions contain oxides or ionic forms of platinum, nickel, copper, cobalt, or palladium which are often present as mixtures of more than one metal. Metal hydrides, such as lithium aluminum hydride [16853-85-3] or sodium borohydride [16940-66-2] can also be used to reduce aldehydes. Depending on additional functionahties that may be present in the aldehyde molecule, specialized reducing reagents such as trimethoxyalurninum hydride or alkylboranes (less reactive and more selective) may be used. Other less industrially significant reduction procedures such as the Clemmensen reduction or the modified Wolff-Kishner reduction exist as well. 

Polyester resins can also be rapidly formed by the reaction of propylene oxide (5) with phthaUc and maleic anhydride. The reaction is initiated with a small fraction of glycol initiator containing a basic catalyst such as lithium carbonate. Molecular weight development is controlled by the concentration of initiator, and the highly exothermic reaction proceeds without the evolution of any condensate water. Although this technique provides many process benefits, the low extent of maleate isomerization achieved during the rapid formation of the polymer limits the reactivity and ultimate performance of these resins. 

In this process, the fine powder of lithium phosphate used as catalyst is dispersed, and propylene oxide is fed at 300°C to the reactor, and the product, ahyl alcohol, together with unreacted propylene oxide is removed by distihation (25). By-products such as acetone and propionaldehyde, which are isomers of propylene oxide, are formed, but the conversion of propylene oxide is 40% and the selectivity to ahyl alcohol reaches more than 90% (25). However, ahyl alcohol obtained by this process contains approximately 0.6% of propanol. Until 1984, ah ahyl alcohol manufacturers were using this process. Since 1985 Showa Denko K.K. has produced ahyl alcohol industriahy by a new process which they developed (6,7). This process, which was developed partiy for the purpose of producing epichlorohydrin via ahyl alcohol as the intermediate, has the potential to be the main process for production of ahyl alcohol. The reaction scheme is as fohows ... 

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