Reduction with aluminum amalgam

A number of sensitive substances can be advantageously reduced by aluminum amalgam since the reaction medium can in this case easily be kept exactly neutral. It is often possible to reduce only one of the conjugated double bonds of fulvenes and indene and fluorene derivatives of analogous structure.27 The process is particularly suitable for hydrogenation of unsaturated esters28,29 that might be hydrolysed in alkaline solution. 

Aluminum amalgam, prepared by Wislicenus method,28 and moist ether are usually used, being allowed to react with the unsaturated compound for 1-2 days with occasional addition of a little water. 

Benzylindene. 1 -Benzylideneindene (5 g) is dissolved in ether and treated, until decolorized, with freshly prepared aluminum amalgam (15 g) with occasional addition of a little water. This requires 6-24 h. The mixture is filtered, the residue is well washed with ether, the solution is dried and freed from ether by distillation, and the residue is fractionated. The resulting benzylindene distils between 183° and 185° at 13 mm. 

Benzylidenefluorene, furfurylidenefluorene, and other derivatives can be similarly reduced.27 

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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. 

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

The oximes of 4,5,6,7-tetrahydrobenzo[6]thiophen-4-one and -7-one undergo the Beckmann rearrangement to give 146 354 451 and 147 (R = H),362 respectively. Compound 147 (R=C1) may be prepared similarly and by treating 2-chloro-4,5,6,7-tetrahydrobenzo[ ]thio-phen-7-one with ammonia in the presence of PPA.356 The oxime of 4,5,6,7 -tetrahydrobenzo [6]thiophene- 4-one affords 4-aminobenzo [6]-thiophene in a modified Leuckart reaction.241,355 The same oxime may be converted into 4-amino-4,5,6,7-tetrahydrobenzo[ ]thiophene by reduction with aluminum amalgam in methanol.452 The parent ketone also affords 4-amino-4,5,6,7-tetrahydrobenzo[6]thiophene on reaction with formamide at 165°, followed by acidic hydrolysis of the resulting 4-formylamino compound.355... 

The aldehyde is also obtained by the hydroformylation of allylbenzene.6 An alternative method involves benzylation of 2-ethylthiazoline followed by reduction with aluminum amalgam and cleavage with mercuric chloride.( A sixth method of preparation is the phenylation of 2-vinyl-5,6-... 

Vinylic sulfoxide (30) is desulfurized to (31) with f-butyllithium (equation 80), and sulfone (32) affords triphenylethylene on reduction with aluminum amalgam or lithium aluminum hydride (equation 81). ... 

The initial syntheses of Cypridina luciferin and its analogues were performed in low yields by reaction of appropriate 2-aminopyrazines with a-keto acids, followed by reduction with aluminum amalgam or catalytic hydrogenation, and treatment of the product with dicyclohexyl-carbodiimide. For example, 2-amino-5-phenylpyrazine (36) on reaction with pyruvic acid gave the product 37, which was reduced to give an intermediate formulated as 38, which was then cyclized to give the 0x0 compound 39 in 7% yield. It was later discovered that these products could be obtained in high yield in one step by reaction of aminopyrazines such as 36 with a-keto aldehydes such as pyruvaldehyde (MeCOCHO). Condensation of the appropriate aminopyrazine with... 

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