Aryl metal compounds, conversion

Alkyl and Aryl Derivatives of the Alkali Halides Useful Synthetic Reagents as Strong Bases and Potent Nucleophiles. 1. Conversion of Organic Halides to Qrganoalkali-Metal Compounds, 2006,25, 2. 

Asymmetric Transfer Hydrogenation of Ketones. The first reports on asymmetric transfer hydrogenation (ATH) reactions catalyzed by chiral metallic compounds were published at the end of the seventies. Prochiral ketones were reduced using alcohols as the hydrogen source, and Ru (274,275) or Ir (276) complexes were used as catalysts. Since then, many chiral catalytic systems for homogeneous ATH of ketones, imines, and olefins have been developed (37,38,256,257,277-289). The catalytic systems are usually based on ruthenium, rhodium, or iridium, and the ATH of aryl ketones is by far the most studied. Because of the reversibility of this reaction, at high conversions, a gradual erosion of the ee of the product has been frequently reported. An azeotropic 5 2 mixture of formic acid/triethylamine can be used to overcome this limitation. 

Next to the formation of Grignard reagents, the most important application of this reaction is the conversion of alkyl and aryl halides to organolithium compounds, but it has also been carried out with many other metals, (e.g., Na, Be, Zn, Hg, As, Sb, and Sn). With sodium, the Wurtz reaction (10-93) is an important side reaction. In some cases, where the reaction between a halide and a metal is too slow, an alloy of the metal with potassium or sodium can be used instead. The most important example is the preparation of tetraethyl lead from ethyl bromide and a Pb—Na alloy. 

The Birch reduction has been used by several generations of synthetic organic chemists for the conversion of readily available aromatic compounds to alicyclic synthetic intermediates. Birch reductions are carried out with an alkali metal in liquid NH3 solution usually with a co-solvent such as THF and always with an alcohol or related acid to protonate intermediate radical anions or related species. One of the most important applications of the Birch reduction is the conversion of aryl alkyl ethers to l-alkoxycyclohexa-l,4-dienes. These extremely valuable dienol ethers provide cyclohex-3-en-l-ones by mild acid hydrolysis or cyclohex-2-en-l-ones when stronger acids are used (Scheme 1). 

The formation of arylzinc reagents can also be accomplished by using electrochemical methods. With a sacrificial zinc anode and in the presence of nickel 2,2-bipyridyl, polyfunctional zinc reagents of type 36 can be prepared in excellent yields (Scheme 14) . An electrochemical conversion of aryl halides to arylzinc compounds can also be achieved by a cobalt catalysis in DMF/pyridine mixture . The mechanism of this reaction has been carefully studied . This method can also be applied to heterocyclic compounds such as 2- or 3-chloropyridine and 2- or 3-bromothiophenes . Zinc can also be elec-trochemically activated and a mixture of zinc metal and small amounts of zinc formed by electroreduction of zinc halides are very reactive toward a-bromoesters and allylic or benzylic bromides . ... 

There are two general routes to arylsulfonyl chlorides. The first involves the conversion of an already sulfur-substituted aromatic compound to the sulfonyl chloride. Thus arylsulfonic acids or their alkali metal salts yield sulfonyl chlorides by treatment with a variety of chlorinating agents such as phosphorus pentachloride, thionyl chloride, phosgene, and chlorosulfonic acid. Alternatively, substituted thiophenols or aryl disulfides can be oxidized by chlorine-water to the sulfonyl chloride.6... 

The nitro group of aromatic nitro compounds has been removed with sodium bor-ohydride. This reaction involves an addition-elimination mechanism. Reduction of the C—N bond on aromatic amines with Li metal in THF generates the aryl compounds.Sodium nitrite, sodium bisulfite in EtOH/water/acetic acid does a similar reduction.Conversion of the aniline derivative to the methanesulfona-mide and subsequent treatment with NaH and NH2CI gives the same result. The BuaSnH reagent also reduces isocyanides, RNC (prepared from RNH2 by for-mylation followed by 17-31), to a reaction that can also be accomplished... 

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