Borohydride, lithium sodium

Lithium Borohydride. Lithium borohydride [16949-15-8] LlBH, is made by metathesis between sodium borohydride and lithium chloride (20) ia isopropylamine. 

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). 

Facial selectivities in the nucleophilic addition of bicyclic ketones have recently been examined comprehensively [71, 72]. Mehta and his colleagues studied the facial selectivities of 2,3-exo,exo-disubstituted 7-norbomanones 14a and 14b [73-75]. In the reduction of 14a and 14b with sodium borohydride, lithium aluminum hydride. 

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... 

Davis, W. D., L. S. Mason, and G. Siegeman The Heats of Formation of Sodium Borohydride, Lithium Borohydride and Lithium Aluminium Hydride. J. Amer. chem. Soc. 71, 2775 (1949). 

The importance of reactions with complex, metal hydrides in carbohydrate chemistry is well documented by a vast number of publications that deal mainly with reduction of carbonyl groups, N- and O-acyl functions, lactones, azides, and epoxides, as well as with reactions of sulfonic esters. With rare exceptions, lithium aluminum hydride and lithium, sodium, or potassium borohydride are the... 

Opening of a bottle where some particles of lithium aluminum hydride were squeezed between the neck and the stopper caused a fire [68]. Lithium aluminum hydride must not be crushed in a porcelain mortar with a pestle. Fire and even explosion may result from contact of lithium aluminum hydride with small amounts of water or moisture. Sodium bis(2-methoxy-ethoxy)aluminum hydride (Vitride, Red-Al ) delivered in benzene or toluene solutions also may ignite in contact with water. Borane (diborane) ignites in contact with air and is therefore kept in solutions in tetrahydrofuran or in complexes with amines and sulfides. Powdered lithium borohydride may ignite in moist air. Sodium borohydride and sodium cyanoborohydride, on the other hand, are considered safe. ... 

Complex hydrides can be used for the selective reduction of the carbonyl group although some of them, especially lithium aluminum hydride, may reduce the a, -conjugated double bond as well. Crotonaldehyde was converted to crotyl alcohol by reduction with lithium aluminum hydride [55], magnesium aluminum hydride [577], lithium borohydride [750], sodium boro-hydride [751], sodium trimethoxyborohydride [99], diphenylstarmane [114] and 9-borabicyclo[3,3,l]nonane [764]. A dependable way to convert a, -un-saturated aldehydes to unsaturated alcohols is the Meerwein-Ponndorf reduction [765]. 

Chemical reduction of aromatic aldehydes to alcohols was accomplished with lithium aluminum hydride [5i], alane [770], lithium borohydride [750], sodium borohydride [757], sodium trimethoxyborohydride [99], tetrabutylam-monium borohydride [777], tetrabutylammonium cyanoborohydride [757], B-3-pinanyl-9-borabicyclo[3.3.1]nonane [709], tributylstannane [756], diphenylstan-nane [114], sodium dithionite [262], isopropyl alcohol [755], formaldehyde (crossed Cannizzaro reaction) [i7i] and others. 

Further reduction of quinones - acquisition of four or more hydrogens per molecule - was achieved with lithium aluminum hydride which reduced, in yields lower than 10%, 2-methyl-1,4-naphthoquinone to 1,2,3,4-tetrahydro-l,4-dihydroxy-2-methylnaphthalene and to l,2,3,4-tetrahydro-4-hydroxy-l-keto-2-methylnaphthalene [931]. Lithium aluminum hydride [931], sodium borohydride, lithium trie thy Iborohydride and 9-borabicyclo[3.3.1Jnomine [100] converted anthraquinone to 9,10-dihydro-9,10-dihydroxyanthracene in respective yields of 67, 65, 77 and 79%. 

Other reagents used for reduction are boranes and complex borohydrides. Lithium borohydride whose reducing power lies between that of lithium aluminum hydride and that of sodium borohydride reacts with esters sluggishly and requires refluxing for several hours in ether or tetrahydrofuran (in which it is more soluble) [750]. The reduction of esters with lithium borohydride is strongly catalyzed by boranes such as B-methoxy-9-bora-bicyclo[3.3.1]nonane and some other complex lithium borohydrides such as lithium triethylborohydride and lithium 9-borabicyclo[3.3.1]nonane. Addition of 10mol% of such hydrides shortens the time necessary for complete reduction of esters in ether or tetrahydrofuran from 8 hours to 0.5-1 hour [1060],... 

Use of more efficient solvents (tetrahydrofuran, isopropyl ether, dimethoxyethane) or more soluble metal hydride reagents (sodium borohydride, lithium tributoxy aluminum hydride, sodium bis(2-methoxyethyl) aluminum hydride) favors the alternative reduction pathway to the hydroquinone. 

Semicarbazones are used as protecting groups as a consequence of their stability to reducing agents such as potassium borohydride,102 sodium boro-hydride89 and lithium borohydride.186 Semicarbazones are cleaved by strong acids and by heating in acetic anhydride-pyridine.145... 

Borane-Dimethylamine, 42 Dimethyl phenylsilane, 123 Diphenylsilane, 153 Lithium aluminum hydride-Sodium methoxide, 159 Potassium-Graphite, 252 Raney nickel, 265 Sodium borohydride, 278 Sodium borohydride-Molybdenum(VI) oxide, 279... 

From carbonyl groups Sodium cyanoborohydride-Zinc iodide, 280 From thioketals Lithium aluminum hydride-Bis-(cyclopentadienyl)nickel, 158 From arenesulfonylhydrazones Sodium borohydride, 278 Sodium cyanoborohydride-Zinc iodide, 280... 

Esters are more difficult to reduce, and usually, no reaction takes place with sodium borohydride. However, the potassium borohydride/lithium chloride system was found to reduce esters under microwave conditions in a solvent-free reaction33. The reactions are generally completed in 2-8 min and provide the corresponding alcohols in 55-95% yield (Scheme 4.13). 

Peptide aldehydes 1 can be synthesized effectively by the oxidation of peptide alcohols 15, which are readily available without racemization by reduction of peptide esters 9 with sodium borohydride-lithium chloride (Scheme 5). The peptide alcohols 15 can be readily oxidized to afford enantiomerically pure aldehydes using Parikh-Doering or Dess-Martin reagents. This route is less popular than the previously described reductive methods due to (1) the sensitivity of the aldehydes to further oxidation, (2) racemization under the reaction conditions, and (3) instability of the products under the reaction conditions. 

REDUCTION, REAGENTS Aluminum amalgam. Borane-Dimethyl sulfide. Borane-Tetrahydrofurane. t-Butylaminoborane. /-Butyl-9-borabicyclo[3.3.1]nonane. Cobalt boride— f-Butylamineborane. Diisobutylaluminum hydride. Diisopropylamine-Borane. Diphenylamine-Borane. Diphenyltin dihydride. NB-Enantrane. NB-Enantride. Erbium chloride. Hydrazine, lodotrimethylsilane. Lithium-Ammonia. Lithium aluminum hydride. Lithium borohydride. Lithium bronze. Lithium n-butylborohydride. Lithium 9,9-di-n-butyl-9-borabicyclo[3.3.11nonate. Lithium diisobutyl-f-butylaluminum hydride. Lithium tris[(3-ethyl-3pentylK>xy)aluminum hydride. Nickel-Graphite. Potassium tri-sec-butylborohydride. Samarium(II) iodide. Sodium-Ammonia. Sodium bis(2-mcthoxyethoxy)aluminum hydride. 

Thioxanthene Butyl lithium Sodium borohydride Dimethylamine 1-Methylpiperazine... 

With Sodium Borohydride, Lithium Aluminum Hydride, Tributyltin Hydride, or Other Group IV-Element Hydrides... 

The new metallic hydrides are excellent reducing agents for carbonyl compounds. These hydrides now include lithium aluminum hydride, lithium borohydride, and sodium borohydride. The last reagent may be used in either aqueous or methanolic solutions. It does not reduce esters, acids, or nitriles and, for this reason, is superior for certain selective reductions. Other groups which are unaffected by this reagent include a,/S-double bonds and hydroxyl, methoxyl, nitro, and dimethylamino groups. ... 

Sodium borohydride or sodium borohydride and trifluoroacetic acid reduce 5- or 6-sub-stituted quinoxalines to the 1,2,3,4-tetrahydro compounds 1.2,3,4-tetrahydroquinoxaline is also formed in the reduction of quinoxaline with bis(trifluoroacetoxy)boranc-tetrahydrofuran. The sodium borohydride reduction of 2,3-dimethylquinoxaline 1,4-dioxide in alcohols affords c 3-2,3-dimethyl-l,2,3,4-tetrahydroquinoxaline as the predominant product and identical to that obtained from the reduction of 2,3-dimethylquinoxaline with lithium aluminum hydride. ... 

Oxycellulose and phenylhydrazine gave a yellow compound, which formed a diphenylformazan, showing that the oxycellulose had reacted in one of the two possible hemiacetal forms. Aminophenols and oxycellulose gave derivatives which coupled with diazonium compounds, enabling chemically colored fibers to be prepared. Reduction of oxycellulose oxime with lithium aluminum hydride, sodium borohydride, or sodium amalgam gave an amino-oxycellulose (109) in which up to 25 % of the oxime groups had been reduced. ... 

Hex-5-enyl-l-mercuric bromide (III) is reduced to 1-hexene (IV) by sodium amalgam, whereas sodium borohydride, lithium aluminum hydride, and tri-77-butyltin hydride gave a mixture of IV and methylcyclopentane. This is taken as evidence that sodium amalgam reduction of alkylmercury salts does not proceed via a free radical pathway [72]. 

The indole ring system is not reduced by nucleophilic reducing agents, such as lithium aluminium hydride or sodium borohydride lithium/liquid ammonia does, however, reduce the benzene ring 4,7-dihydroindole is the main product. ... 

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