Lithium derivatives Reducing agents

Most classical reducing agents leave the pyrimidine nucleus unaffected, as does sodium borohydride lithium aluminium hydride usually gives a di- or tetra-hydro derivative, according to substituent(s) present (70HC(16-S1)322). 

Oral progestational activity is retained when the ketone at the 3 position is reduced to an alcohol. Treatment of ethindrone (13-6) with the bulky reducing agent lithium aluminum-tri-ferf-butoxy hydride leads to attack from the more open a face and the formation of the 3 3 hydroxy derivative (14-1). Acylation under forcing conditions affords the 3,17-diacetate derivative, ethynodiol diacetate (14-2) [17]. 

When the reaction between a trialkylborane and carbon monoxide (8-24) is carried out in the presence of a reducing agent such as lithium borohydride or potassium triisopropoxy-borohydride, the reduction agent intercepts the intermediate 73, so that only one boron-to-carbon migration takes place, and the product is hydrolyzed to a primary alcohol or oxidized to an aldehyde.333 This procedure wastes two of the three R groups, but this problem can be avoided by the use of B-alkyl-9-BBN derivatives (p. 785). Since only the 9-alkyl group... 

Lithium aluminum hydride usually reduces carbonyl groups without affecting carbon-carbon double bonds. It is, in addition, a good reducing agent for carbonyl groups of carboxylic acids, esters, and other acid derivatives, as will be described in Chapter 18. 

Alcohols are at a fairly low oxidation level compared to other oxygen-containing functional groups and consequently are readily prepared by reduction. Large numbers of reductive methods have been reported for the preparation of alcohols. Carboxylic acids and esters react vigorously with lithium aluminum hydride (LAH) to produce primary alcohols. Carboxylic acids, but not esters, are also reduced easily by borane, which is die only reducing agent diat reacts faster widi carboxylic acids dian widi esters or odier acid derivatives. 

Carboxylic acids, acid halides, esters, and amides are easily reduced by strong reducing agents, such as lithium aluminum hydride (LiAlH4). The carboxylic acids, acid halides, and esters are reduced to alcohols, while the amide derivative is reduced to an amine. 

Carboxylic acids and their derivatives can be reduced to alcohols, aldehydes, and amines. Because they are relatively difficult to reduce, acid derivatives generally require a strong reducing agent such as lithium aluminum hydride (LiAlH4). 

Acid chlorides are more reactive than other acid derivatives, and they are reduced to aldehydes by mild reducing agents such as lithium tri-ferf-butoxyaluminum hydride. Diisobutylaluminum hydride (DIBAL-H) reduces esters to aldehydes at low temperatures, and it also reduces nitriles to aldehydes. These reductions were covered in Sections 18-9,18-10, and 20-13. 

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