Reduction aluminum, amalgamated

Reduction of dihyro compounds to the tetrahydro derivatives is sometimes possible. For example, thiazolines are reduced to thiazolidines by aluminum amalgam. 

Benzopinacol has been prepared by the action of phenylmag-nesium bromide on benzil 1 or methyl benzilate. Usually it has been obtained by reduction of benzophenone, the reducing agents being zinc and sulfuric acid or acetic acid, aluminum amalgam, and magnesium and magnesium iodide. The present... 

C. Reduction of )3-Keto Sulfoxides with Aluminum Amalgam (//)... 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

The sonochemical-promoted aluminum amalgam reduction of P-nitro alcohols provides an improved yield and accelerated conversion to the corresponding amino alcohols.108... 

That propargylic starting materials are often employed in modern allene hydrocarbon chemistry is not surprising and the following examples are just a small selection from a much larger synthetic effort. Thus, the sulfones 61 are first cleaved in an aluminum amalgam-mediated reduction to the intermediates 62, which lose sulfur dioxide under the reaction conditions and furnish the trisubstituted allenes 63 in good to excellent yields (75-95%) (Scheme 5.7) [18]. 

A different approach to the stereospecific synthesis of sulfinamides described by Johnson (117,118) is based on the conversion of suitable chiral tetracoordinate sulfur compounds into sulfinamides. It was shown (117) that optically active methyl phenyl sulfoximide undergoes a clean and stereospecific reduction to the corresponding sulfinamide by means of aluminum amalgam. On the other hand,... 

Oxidative cyclization, substituted stil-benes to phenanthrenes, 46, 91 Oximes, reduction with lithium aluminum hydride, 48, 23 Oximinomalononitrile, from nitrosation of malononitrile, 48,1 reduction with aluminum amalgam, 48,2 ... 

B. N-t-Butylhydroxylamine. Caution Since hydrogen may he liberated during the reduction with aluminum amalgam, the reaction should he conducted in a hood. Also, the aluminum amalgam may he pyrophoric. Consequently, it should he used, immediately and not allowed to become dry. 

Reductions with aluminum are carried out almost exclusively with aluminum amalgam. This is prepared by immersing strips of a thin aluminum foil in a 2% aqueous solution of mercuric chloride for 15-60 seconds, decanting the solution, rinsing the strips with absolute ethanol, then with ether, and cutting them with scissors into pieces of approximately 1 cm [141,142]. In aqueous and non-polar solvents aluminum amalgam reduces cumulative double bonds [143], ketones to pinacols [144], halogen compounds [145], nitro compounds [146, 147], azo compounds [148], azides [149], oximes [150] and quinones [151], and cleaves sulfones [141, 152, 153] and phenylhydrazones [154] (Procedure 30, p. 212). 

Nitroso compounds are usually not obtained directly but rather by reoxidation of hydroxylamino compounds or amines. Hydroxylamino compounds are prepared by electrolytic reduction using a lead anode and a copper cathode [573], by zinc in an aqueous solution of ammonium chloride [574 or by aluminum amalgam [147], generally in good yields. 

In addition to deoxygenation sulfoxides undergo reductive cleavage at the carbon-sulfur bond when heated in tetrahydrofuran with aluminum amalgam. Keto sulfoxides were thus converted to ketones in usually quantitative yields (the keto group remained intact) [141]. 

For the reduction to pinacols aluminum amalgam [825] or low valence state titanium chloride [207] were used. Under different conditions the titanium... 

Metal amalgams may be used for reduction of the keto groups in keto esters provided the medium does not cause hydrolysis of the ester. Because of that aluminum amalgam in ether is preferable to sodium amalgam in aqueous solutions. Diethyl oxalacetate was reduced to diethyl malate by sodium amalgam in 50% yield and with aluminum amalgam in 80% yield [148], Stereospecific reduction of a- and fi-keto esters to optically pure hydroxy esters was achieved by biochemical reduction in moderate to good yields. Saccharomyces cerevisiae converted methyl 2-keto-2-phenylacetate to methyl... 

Reduction of oximino esters, i.e. oximes of keto esters, is very useful for the preparation of amino esters. Reductions are very selective since the oximes are easily reduced by catalytic hydrogenation over 10% palladium on carbon in ethanol (yield 78-82%) I094, by aluminum amalgam in ether (yields 52-87%) [750, 70P5], or by zinc dust in acetic acid (yield 77-78%). None of these reagents attacks the ester group. The last mentioned reaction gives an N-acetyl derivative [1096. ... 

REDUCTION WITH ALUMINUM AMALGAM Reduction of Aliphatic-Aromatic Ketones to Pinacols [144]... 

Aluminum amalgam reduces aUphatic 53 aromatic nitro compounds to hydroxylamines in consistently good yields (equation 51) and this can be the method of choice for large-scale reductions. 

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