Methylamine dissolving metal reduction

Double bonds conjugated with benzene rings are reduced electrolytically [344] (p. 23). Where applicable, stereochemistry can be influenced by using either catalytic hydrogenation or dissolving metal reduction [401] (p. 24). Indene was converted to indane by sodium in liquid ammonia in 85% yield [402] and acenaphthylene to acenaphthene in 85% yield by reduction with lithium aluminum hydride in carbitol at 100° [403], Since the benzene ring is not inert toward alkali metals, nuclear reduction may accompany reduction of the double bond. Styrene treated with lithium in methylamine afforded 25% of 1-ethylcyclohexene and 18% of ethylcyclohexane [404]. 

A variety of ketones or aldehydes may be reduced to an alcohol using dissolving metal reduction. Alcohols other than ethanol are used as solvents, and low boiling amines such as methylamine or dimethylamine can be used in place of ammonia. Other alkali metals such as lithium or calcium also work. Lithium in a mixture of methylamine and ethanol, and calcium metal in methylamine may also be used in these reduction reactions, primarily on large-scale reactions such as those found in industrial laboratories or factories. 

Carbon-carbon double bonds are often stable to dissolved metals. Considerable amounts of norbornane (54) are obtained when either norbomadiene (53) or nor-bornene (56) is reduced by calcium in methylamine-ethylenediamine (Scheme 4.15) [35]. The C-C double bonds in both substrates are highly strained, which enables the reduction to proceed smoothly. In the reduction of diene 53, a tricyclic compound 55 is produced as a by-product in 18% yield. 

Birch reduction11 is the partial reduction of aromatic rings by solvated electrons produced when alkali metals dissolve (and react) in liquid amines. Typical conditions are sodium in liquid ammonia or lithium in methylamine. These electrons add to benzene rings to produce, probably, a dianion 57 that is immediately protonated by a weak acid (usually a tertiary alcohol) present in solution. The anions in the supposed intermediate 57 keep as far from each other as they can so the final product is the non-conjugated diene 58. It is important to use the blue solution of solvated electrons before it reacts to give hydrogen and NaNH2. 

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