Lithium catalysis

Several new methods for the preparation of 1-haloalkynes have been described. High yields of bromo compounds, e.g. 28, are obtained by treatment of alkynes with triphenylphosphine/carbon tetrabromide, or with a concentrated aqueous solution of potassium hypobromite and potassium hydroxide (equation 1). 1-Iodoalkynes are produced from terminal alkynes and bis(pyridine)iodine(I) tetrafluoroborate in methanol in the presence of sodium methoxide (equation 2) or from alkynes with a mixture of iodine, potassium carbonate, copper(I) iodide and tetrabutylammonium chloride under phase-transfer catalysis. Lithium acetylides 29 (R = Ph, t-Bu, HOCH2 etc.) react with zinc iodide and bis(trimethylsilyl) peroxide to yield 1-iodoalkynes. The method has been... 

The cyclization step requires Lewis acid catalysis lithium chloride, formed during an attempt at silylation, is sufficient. The stereochemical course under these conditions (retention at the carbanionic center, inversion at C-3) was rigorously proven by stereospecific deuteration, and an X-ray structure analysis of amino ketone 171, as well [57]. Surprisingly, the use of the stronger Lewis acids f-BuMe2SiOTf or Bp3-OEt2 caused the formation of the opposite enantiomer ent-169 [57] the reasons are still unknown. The cyclopropanes 169 are easily depro-tonated by sec-butyllithium/TMEDA and substituted by many electrophiles with complete retention [57]. The reactions are quite general diastereomers are formed from 2-monosubstituted dicarbamates [108]. 

Vanadium oxide (VOx) is relevant to a multitude of catalytic reactions [1]. Amongst various open, metastable VOx phases containing organic species or metal cations, vanadium oxide nanotubes (VOx-NTs) and derivatives thereof can be prepared via hydrothermal synthesis. Thanks to their unique layered stmcture and the simultaneous presence of vanadium in various oxidation states, VOx-NTs are interesting with re rd to catalysis, lithium intercalation in batteries and sensor applications [2,3,4],... 

Aryl sulfides are prepared by the reaction of aryl halides with thiols and thiophenol in DMSO[675,676] or by the use of phase-transfer catalysis[677]. The alkenyl sulfide 803 is obtained by the reaction of lithium phenyl sulfide (802) with an alkenyl bromide[678]. 

The first successhil use of lithium metal for the preparation of a i7j -l,4-polyisoprene was aimounced in 1955 (50) however, lithium metal catalysis was quickly phased out in favor of hydrocarbon soluble organ olithium compounds. These initiators provide a homogeneous system with predictable results. Organ olithium initiators are used commercially in the production of i7j -l,4-polyisoprene, isoprene block polymers, and several other polymers. 

Ca.ta.lysts, A small amount of quinoline promotes the formation of rigid foams (qv) from diols and unsaturated dicarboxyhc acids (100). Acrolein and methacrolein 1,4-addition polymerisation is catalysed by lithium complexes of quinoline (101). Organic bases, including quinoline, promote the dehydrogenation of unbranched alkanes to unbranched alkenes using platinum on sodium mordenite (102). The peracetic acid epoxidation of a wide range of alkenes is catalysed by 8-hydroxyquinoline (103). Hydroformylation catalysts have been improved using 2-quinolone [59-31-4] (104) (see Catalysis). 

The product described here, 4-(4-chlorophenyl)butan-2-one, was previously prepared in the following ways a) by reduction of the corresponding benzalacetone, b) by catalyzed decarbonylation of 4-chlorophenylacetaldehyde by HFeiCO) in the presence of 2,4-pentanedione, - c) by reaction of 4-chlorobenzyl chloride with 2,4-pentanedione under basic catalysis (K2CO3 in EtOH), d) by reaction of 4-chlorobenzyl chloride with ethyl 3-oxobutanoate under basic catalysis (LiOH), - and e) by reaction of 3-(4-chlorophenyl )-propanoic acid with methyl lithium. - ... 

Resoles are usually those phenolics made under alkaline conditions with an excess of aldehyde. The name denotes a phenol alcohol, which is the dominant species in most resoles. The most common catalyst is sodium hydroxide, though lithium, potassium, magnesium, calcium, strontium, and barium hydroxides or oxides are also frequently used. Amine catalysis is also common. Occasionally, a Lewis acid salt, such as zinc acetate or tin chloride will be used to achieve some special property. Due to inclusion of excess aldehyde, resoles are capable of curing without addition of methylene donors. Although cure accelerators are available, it is common to cure resoles by application of heat alone. 

In addition to the formulation parameters mentioned above, selection of the base used for catalysis has strong implications. Bases commonly used are sodium hydroxide, potassium hydroxide, lithium oxide, calcium hydroxide, barium hy-... 

As an alternative to lithium enolates. silyl enolates or ketene acetals may be used in a complementary route to pentanedioates. The reaction requires Lewis acid catalysis, for example aluminum trifluoromethanesulfonate (modest diastereoselectivity with unsaturated esters)72 74 antimony(V) chloride/tin(II) trifluoromethanesulfonate (predominant formation of anti-adducts with the more reactive a,/5-unsaturated thioesters)75 montmorillonite clay (modest to good yields but poor diastereoselectivity with unsaturated esters)76 or high pressure77. 

The Diels-Alder reaction of nonyl acrylate with cyclopentadiene was used to investigate the effect of homochiral surfactant 114 (Figure 4.5) on the enantioselectivity of the reaction [77]. Performing the reaction at room temperature in aqueous medium at pH 3 and in the presence of lithium chloride, a 2.2 1 mixture of endo/exo adducts was obtained with 75% yield. Only 15% of ee was observed, which compares well with the results quoted for Diels-Alder reactions in cyclodextrins [65d]. Only the endo addition was enantioselective and the R enantiomer was prevalent. This is the first reported aqueous chiral micellar catalysis of a Diels-Alder reaction. 

Initially the LP-DE effect was ascribed to the high internal pressure generated by the solubilization of the salt in diethyl ether [34]. Today the acceleration is explained in terms of Lewis-acid catalysis by the lithium cation [35]. The contribution of both factors (internal pressure and lithium cation catalysis) has also been invoked [36]. 

Catalysis by lithium perchlorate in dichloromethane Diels-Alder reactions and 1,3-Claisen rearrangements [100]... 

With aliphatic amines, the decomposition catalysis is moderate with heterocyclic aromatic amines (pyridine, quinoline), 0.1 % of amine is sufficient to cause maleic anhydride to decompose. An accident has also been mentioned with NaOH. This decomposition also takes place in the presence of sodium, lithium, ammonium, potassium, calcium, barium, magnesium and beryllium cations. 

Lithium fefrafc/s-(3,5-ditrifluoromethyl)borate, which provides an unsolvated lithium cation in noncoordinating solvents, exhibits a several thousandfold catalysis of the reaction of cyclopentadiene and methyl vinyl ketone.37 Lithium tetrafluoroborate is also an effective catalyst and in some instances has worked when LiC104 has failed, such as in the intramolecular reaction shown below.38... 

Dyashkovskii and Shilov [Kinetics and Catalysis, 4 (808), 1963] have studied the kinetics of the reaction between ethyl lithium and ethyl iodide in decalin solution. 

Metal complexes of pinene-fused boratabenzene ligands, analogous to chiral metallocenes that have found application in catalysis and enantioselective synthesis, have been prepared.122-124 With late transition metals such as Mn and Fe, the complexes are obtained as mixtures of diastereomers (e.g., 97) with the sterically less congested exo form predominating, but the bis(ligand) Zr complex 98 was obtained as the pure exo,exo product.124 A lithium... 

---