Phase-transfer catalysis, copper catalysts

This reaction is similar to 13-1 and, like that one, generally requires activated substrates. With unactivated substrates, side reactions predominate, though aryl methyl ethers have been prepared from unactivated chlorides by treatment with MeO in HMPA. This reaction gives better yields than 13-1 and is used more often. A good solvent is liquid ammonia. The compound NaOMe reacted with o- and p-fluoronitrobenzenes 10 times faster in NH3 at — 70°C than in MeOH. Phase-transfer catalysis has also been used. The reaction of 4-iodotoluene and 3,4-dimethylphenol, in the presence of a copper catalyst and cesium carbonate, gave the diaryl ether (Ar—O—Ar ). Alcohols were coupled with aryl halides in the presence of palladium catalysts to give the Ar—O—R ether. Nickel catalysts have also been used. ... 

The reaction with ammonia or amines, which undoubtedly proceeds by the SnAt mechanism, is catalyzed by copper and nickel salts, though these are normally used only with rather unreactive halides. This reaction, with phase-transfer catalysis, has been used to synthesize triarylamines. Copper ion catalysts (especially cuprous oxide or iodide) also permit the Gabriel synthesis (10-61) to be... 

The synthesis of the chiral copper catalyst is very easy to reproduce. The complex catalyses the asymmetric alkylation of enolates of a range of amino acids, thus allowing the synthesis of enantiomeric ally enriched a,a disubstituted amino acids with up to 92% ee. The procedure combines the synthetic simplicity of the Phase Transfer Catalyst (PTC) approach, with the advantages of catalysis by metal complexes. The chemistry is compatible with the use of methyl ester substrates, thus avoiding the use of iso-propyl or ferf-butyl esters which are needed for cinchona-alkaloid catalyzed reactions[4], where the steric bulk of the ester is important for efficient asymmetric induction. Another advantage compared with cinchona-alkaloid systems is that copper(II)(chsalen) catalyses the alkylation of substrates derived from a range of amino acids, not just glycine and alanine (Table 2.4). 

Another report concerning the trifluoromethylation of alkenes under copper catalysis based on gas-phase DFT calculations comes to a different conclusion [50]. This study points to a radical mechanism, with the copper(I) catalyst reducing reagent 1 by means of a single electron transfer (SET) as the key step in the catalytic cycle. 

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