Hydride agents

After a metal hydride complex was prepared from LAH and quinine (1 1), irradiation of a mixture of the resulting solution containing the above chiral hydride agent and the enamide (133) led to the formation of two optically active lactams 158 [6%, [a]D —63° (c = 0.48, CHC13)] and 155 [ 13%, [a]D — 102° (c = 0.44, CHC13)] with 37% optical purity. Reduction of the lactam 155 with LAH furnished (—)-xylopinine (20) in 48% chemical yield. 

MECHANISM 20.9 THE REDUCTION OF KETONES OR ALDEHYDES WITH HYDRIDE AGENTS... 

LiAKOBujaH. A selective reducing agent for converting RCOCl to aldehydes and reducing steroid ketones. See aluminium hydride. 

Hi at 500" C. Stable crystalline compound, gives LiOH and Hi with water (may ignite in moist atmosphere). Used as a source of Hi, as a reducing agent, and for the preparation of hydrides. 

LiAlH4, lithium tetrahydridoaluminate ("lithium aluminium hydride . so-called) is an excellent reducing agent in ether solution for both organic and inorganic compounds it may be used to prepare covalent hydrides SiH ether, for example... 

It is a colourless gas which decomposes on heating above 420 K to give metallic tin, often deposited as a mirror, and hydrogen. It is a reducing agent and will reduce silver ions to silver and mercury(II) ions to mercury. SnSn bonding is unknown in hydrides but does exist in alkyl and aryl compounds, for example (CH3)3Sn-Sn(CH3)3. 

Group V hydrides are reducing agents, the reducing power increasing from NH3 to BiHa, as thermal stability decreases. 

Both the acid and its salts are powerful reducing agents. They reduce, for example, halogens to halides, and heavy metal cations to the metal. Copper(H) ion is reduced further to give copper(I) hydride, a red-brown precipitate ... 

These closely resemble the corresponding sulphides. The alkali metal selenides and tellurides are colourless solids, and are powerful reducing agents in aqueous solution, being oxidised by air to the elements selenium and tellurium respeetively (cf. the reducing power of the hydrides). 

Lithium aluminium hydride, LiAlH, is a very active reducing agent, and is used particularly for the ready reduction of carboxylic acids (or their esters) to primary alcohols R-COOH -> R CH,OH. 

Some of the functional groups which are reduced by lithium aluminium hydride, the reduction product together with the theoretical mols of reducing agent required (in parenthesis) are listed below —... 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

Common reducing agents are hydrogen in the presence of metallic or complex catalysts (e.g. Ni, Pd, Pt, Ru, Rh), hydrides (e.g. alanes, boranes, LIAIH, NaBHJ, reducing metals (e.g. Li, Na, Mg, Ca, Zn), and low-valent compounds of nitrogen (e.g. NjHj, NjHJ, phosphorus (e.g. triethyl phosphite, triphenyiphosphine), and sulfur (e.g. HO-CHj-SOjNa = SFS, sodium dithionite = Na S O. ... 

Hajos, A. 1979, Complex Hydrides and Related Reducing Agents in Organic Synthesis, Elsevier Amsterdam New York... 

For most laboratory scale reductions of aldehydes and ketones catalytic hydro genation has been replaced by methods based on metal hydride reducing agents The two most common reagents are sodium borohydride and lithium aluminum hydride... 

Carboxylic acids are exceedingly difficult to reduce Acetic acid for example is often used as a solvent in catalytic hydrogenations because it is inert under the reaction con ditions A very powerful reducing agent is required to convert a carboxylic acid to a pri mary alcohol Lithium aluminum hydride is that reducing agent... 

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