Lithium as reducing agent

There have been numerous reports on the reduction of activated cyclopropanes with alkali metals either dissolved in liquid ammonia or used in suspension. Most of these reactions were carried out with lithium as reducing agent. In an early study, various substituted cyclopropyl ketones were treated with lithium in liquid ammonia. rranj-l-Acetyl-2-methylcyclopropane (1, R = Me = H R = Me) gave 3,4,4-trimethyl-2-pentanone (3) as the result of... 

Other practical applications of the alkali metals and their compounds include sodium and potassium in living systems, lithium as treatment for bipolar disorder (manic depression), elemental sodium and lithium as reducing agents, lithium in a new generation of batteries, cesium in photoelectric devices, potassium-argon dating, and lithium as a source of tritium to fuel the hydrogen economy. 

Azo, azoxy, and hydrazo compounds can all be reduced to amines. Metals (notably zinc) and acids, and Na2S204, are frequently used as reducing agents. Borane reduces azo compounds to amines, though it does not reduce nitro compounds. " Lithium aluminum hydride does not reduee hydrazo compounds or azo compounds, though with the latter, hydrazo compounds are sometimes isolated. With azoxy compounds, LiAHLj gives only azo compounds (19-48). 

Alkylborohydrides are also used as reducing agents. These compounds have greater steric demands than the borohydride ion and therefore are more stereoselective in situations in which steric factors come into play.72 These compounds are prepared by reaction of trialkylboranes with lithium, sodium, or potassium hydride.73 Several of the compounds are available commercially under the trade name Selectrides .74... 

The use of calcium in place of the rare-earth alloy as the reducing agent gives a product containing from 91 to 93 per cent, of vanadium, while a mixture of calcium and aluminium produces 94 5 per cent, pure vanadium. Lithium has been used as reducing agent, vanadium of 99 per cent, purity being claimed.7... 

Sodium amalgam and elemental lithium have also been used as reducing agents in the preparation of [Ni(PPh3)2(CH2CCH2)]65 and [Ni(PPh3)2(PhCHCHPh)].154... 

In recent years, inorganic hydrides such as lithium aluminum hydride, LiAlH4, and sodium borohydride, NaBH4, have become extremely important as reducing agents of carbonyl compounds. These reagents have considerable utility, especially with sensitive and expensive carbonyl compounds. The reduction of cyclobutanone to cyclobutanol is a good example, and you will... 

Lithium aluminum hydride as reducing agent permits formation of alcohol 40 in the first step. This is then convened to iodide 41. Another reduction with a nucleophilic boron reagent produces an ethyl group at C-13 and thus structure 12. 

With lithium aluminum hydride as reducing agent in tetrahydrofuran, bis[4-inethoxyphenyl] dilellurium was obtained in 93% yield1. 

Dialkyl and diaryl ditellurium compounds are easily reduced to tellurols and tellurolates. Alkali metals in liquid ammonia or in an inert organic solvent, sodium borohydride in methanol, ethanol, alcohol/benzene, THF, DMF, or in a basic aqueous medium, lithium aluminum hydride in dioxane or THF/hexamethylphosphoric triamide, and thiourea dioxide in THF/50% aqueous sodium hydroxide have been used as reducing agents (p. 164). The tellurolates are easily oxidized in air. For this reason they are almost always used in situ. 

The reaction of methyllithium with dimethylzinc in 1 1 and 2 1 molar ratios in diethyl ether solution produces lithium tri- and tetramethyl-zincates.1 Two equivalents of lithium trimethylzincate( 1 -) react with three equivalents of lithium tetrahydridoaluminate(l -), and one equivalent of lithium tetramethylzincate(2 —) reacts with two equivalents of lithium tetra-hydridoaluminate(l —) to give lithium trihydridozincate( 1 -) and lithium tetrahydridozincate(2 —), respectively, in quantitative yields. Both reactions proceed in diethyl ether at room temperature and are complete within 5 min. The compounds are air-sensitive and therefore must be prepared in an airfree atmosphere (nitrogen or argon). They may be used as reducing agents in organic syntheses. 

The tetrahydroborate salts of alkali metals, M[BH4] (M = Li, Na, K),1 are important because they serve as starting materials for the preparation of other boron hydrides2,3 and because they are used frequently as reducing agents.4 The lithium and sodium salts are prepared on a technical scale.5 9 The tetrahydroborate salts of the alkaline earth metals, M[BH4]2 (M = Mg, Ca, Sr, Ba), have not as yet been used extensively however, calcium bis[tetrahydroborate(l-)], Ca(BH4)2,10 is very soluble in tetrahydrofuran (THF) and it therefore has considerable potential application as a substitute for the lithium and sodium salts. 

As shown in equation 2, the lithium enolate oxidation with O2, followed by sodium sulphite reduction, has been applied with success to oxidation of the enolate derived from 1 the nature of the reducing agent has been decisive for the direct preparation of the hepatoprotective agent Clausenamide (2). As a matter of fact, 2 forms when the treatment with O2 is done in the presence of triethyl phosphite as reducing agent, whereas sodium sulphite reduction affords compound 3. It has been postulated that the transformation 1 —3 occurs through the intermediacy of the peroxide 4. 

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