Sodium borohydride carbonyl groups

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... 

Other reagents which have occasionally been used to cleave hydrazides include diborane (which also reduces the carbonyl groups), sodium naphthalenide, 0,0-diethyldithiophosphoric acid, (EtO)2PS2H, - and sulfur monochloride. Nickel-aluminum alloy in aqueous methanolic potassium hydroxide is a good reagent for reductively cleaving a number of N—N bonded compounds, such as A -methyl-A -phenylhydrazine and Af/Z-dimethylnitrosamine. - Nitrosamines have also been cleaved with titanium(IV) chloride-sodium borohydride and lithium aluminium hydride. 

The reduction of the maleic anhydride adduct (303) with lithium aluminium hydride was previously reported to occur selectively to give the lactone (304). The lower selectivity now observed with sodium aluminium hydride (none at all with sodium borohydride) is interpreted as evidence for a complex (305) of the ester and anhydride carbonyl groups with a solvated lithium ion when lithium aluminium hydride is used, leading to selective reduction of the free carbonyl group.Sodium ions are considered not to form so stable a complex. 

Spiradine D. This alkaloid from S. japonica was shown to contain a carbonyl group, an exocyclic methylene group, and an ether group. Sodium borohydride... 

Neither sodium borohydride nor lithium aluminum hydride reduces isolated carbon-carbon double bonds This makes possible the selective reduction of a carbonyl group m a molecule that contains both carbon-carbon and carbon-oxygen double bonds... 

Nucleophilic addition to carbonyl groups sometimes leads to a mixture of stereoisomeric products The direction of attack is often controlled by stenc factors with the nude ophile approaching the carbonyl group at its less hindered face Sodium borohydride reduction of 7 7 dimethylbicyclo[2 2 IJheptan 2 one illustrates this point... 

The enzyme is a single enantiomer of a chiral molecule and binds the coenzyme and substrate m such a way that hydride is transferred exclusively to the face of the carbonyl group that leads to (5) (+) lactic acid Reduction of pyruvic acid m the absence of an enzyme however say with sodium borohydride also gives lactic acid but as a racemic mixture containing equal quantities of the R and S enantiomers... 

The well-known reduction of carbonyl groups to alcohols has been refined in recent studies to render the reaction more regioselective and more stereoselective Per-fluorodiketones are reduced by lithium aluminum hydride to the corresponding diols, but the use of potassium or sodium borohydride allows isolation of the ketoalcohol Similarly, a perfluoroketo acid fluonde yields diol with lithium aluminum hydnde, but the related hydroxy acid is obtainable with potassium borohydnde [i f] (equations 46 and 47)... 

The carbonyl group of carbohydrates can be reduced to an alcohol function. Typical procedures include catalytic hydrogenation and sodium borohydride reduction. Lithium aluminum hydride is not suitable, because it is not compatible with the solvents (water, alcohols) that are requited to dissolve caibohydrates. The products of caibohydrate reduction aie called alditols. Because these alditols lack a car bonyl group, they aie, of course, incapable of forming cyclic hemiacetals and exist exclusively in noncyclic forms. 

Reduction (Section 25.18) The carbonyl group of aldoses and ketoses is reduced by sodium borohydride or by catalytic hydrogenation. The products are called alditols. 

Two classes of aldolase enzymes are found in nature. Animal tissues produce a Class I aldolase, characterized by the formation of a covalent Schiff base intermediate between an active-site lysine and the carbonyl group of the substrate. Class I aldolases do not require a divalent metal ion (and thus are not inhibited by EDTA) but are inhibited by sodium borohydride, NaBH4, in the presence of substrate (see A Deeper Look, page 622). Class II aldolases are produced mainly in bacteria and fungi and are not inhibited by borohydride, but do contain an active-site metal (normally zinc, Zn ) and are inhibited by EDTA. Cyanobacteria and some other simple organisms possess both classes of aldolase. 

Preparation of the prototype starts with the radical side I liain bromination of dichloroacetophenone to give the bromoketone (23). The carbonyl group is then reduced by means of sodium borohydride displacement of halogen by means of isopropylamine... 

Condensation of piperazine with 2-methoxytropone gives the addition-elimination product 12 [2]. Alkylation of the remaining secondary amino group with bromoketone 13, itself the product from acylation of dimethyl catechol, gives aminoketone 14. Reduction of the carbonyl group with sodium borohydride leads to secondaiy alcohols 15 and 16. Resolution of these two enantiomers was achieved by recrystallization of their tartrate salts to give ciladopa (16) [3],... 

Acylation of 14 with cyclobutylcarbonyl chloride followed by the same series of transformations as above leads to intermediate 22. Reduction of the carbonyl group in that molecule with sodium borohydride gives the analgesic agonist/antagonist nalbuphine (23). 7... 

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... 

In the other approach, again harmalane (150) was treated with methyl 2-(di-ethylphosphono)acrylate (174), resulting in iminophosphonate 175. By its sodium borohydride reduction and subsequent lactonization, the amidophospho-nate 176 has been obtained, Wittig-Homer reaction of 176 with acetaldehyde followed by selective reduction of the carbonyl group of the enamide function supplied ( )-deplancheine in good yield (116). 

Sodium borohydride is a much milder reducing agent than lithium aluminium hydride and like the latter is used for the reduction of carbonyl compounds like aldehydes and ketones. However, under normal conditions it does not readily reduce epoxides, esters, lactones, acids, nitriles or nitro groups. 

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