Reduction by sodium borohydride

Table 7. Summary of Inorganic Reductions by Sodium Borohydride ...

Norbomenone 26 undergoes reduction by sodium borohydride under kinetic conditions to produce 5% exo- (i.e., endo attack) and 95% endo- (i.e., exo attack) 2-norbomeol. This leads to the partial rate constants of 11.4 for exo and 0.6 for endo attack (relative rate with respect to the rate of LiAlH reduction of cyclopen-tanone (1.00)) [80]. In the saturated 2-norbomanone 25, the values are 4.55 for exo and 0.74 for endo attack. Thus, the introduction of the double bond enhances the... 

Addition of lithiated heterocycles to aldonolactones yields carbon-linked nucleosides (56). Thus, the reaction of 2,3 5,6-di-O-isopropylidene-L-gu-lono-1,4-lactone (9b) or 2,3-O-isopropylidene-D-ribono-l,4-lactone (16a) with various lithiated heterocycles gave gulofuranosyl derivatives 53a-g or ribofuranosyl derivatives 54b,c. Gulonolactols 53a-g and ribonolactols 54b,c were acetylated with acetic anhydride in pyridine to yield their acetyl derivatives. The stereochemistry of compounds 53a-g and 54b,c was discussed in terms of the Cotton effect of circular-dichroism curves of the ring-opened alcohols formed upon reduction by sodium borohydride. The configuration at C-l of 53g was proved by means of X-ray analysis (57,58). 

Wee, T. G., Frey, P. A. Studies on the mechanism of action of uridine diphosphate galactose 4-epimerase. Substate dependent reduction by sodium borohydride. J. Biol. Chem. 248, 33—40 (1973). 

Explain the higher reactivity of acetone (propanone) compared to methyl acetate (CH3CO2CH3) toward reduction by sodium borohydride. 

IV,B,2). Successful reduction by sodium borohydride has been reported only for quaternary salts 161228 and 16265 the reported sites of reduction differed. 

The mesomeric quinonemethides and 0-quinonemethides described above are somewhat more stable than the simple p-quinonemethides whose properties are already well known even from classical studies. The o-quinonemethides XX and XVII do not add on water even in solution in aqueous organic solvents their solution in dioxane/water is stable for months. They do not add on methanol or higher alcohols and react only slowly with phenols and organic acids. The addition of water is not catalyzed by mild alkalies the red color of the phenoxide ion (XVIII) prevails for weeks in soda solution. Addition of water occurs more rapidly in strongly alkaline solution. The addition of mineral acids and reduction by sodium borohydride are instantaneous. The addition of HC1 is rapid even at pH 4.0, the conditions used for determining the carbonyl content of lignin by the hydroxylamine hydrochloride reaction 13). 

A triflate group undergoes ready reduction by sodium borohydride. The reaction has been applied to the preparation of methyl 2,3,6-tri-0-benzyl-4-deoxy-a-D-xy/o-hexopyranoside. By using sodium borodeuteride, the 4-deoxy-a-d-(4- 2H)-galactopyranoside was obtained.93... 

The reduction of a pyridinium ion in the presence of hydrogen cyanide has been shown to produce substituted 6-cyano-l,2,5,6-tetrahydropyridines. The cyanide competes with the borohydride ion for reaction with the protonated dihydropyxidine intermediate. The cyanide addition can be reversed, and this reaction, therefore, provides a method of protecting the intermediate dihydropyridine from reduction by sodium borohydride.47"... 

You could comparethis,reactlon with reduction by sodium borohydride (Chapter 6). Hydride is transferred from a boron atom to a carbonyl group but no free hydride is formed. 

Pd-C in both ethanol and DMF, little, if any, selectivity was obtained product ratios were 50 50 in ethanol and 60 40 in DMF. Palladium black in ethanol, which afforded 4-amino-5-nitroveratrole in 70-75% yield from 4,5-dinitroveratrole, provided no selectivity with 2,4-dinitroaniline, as well as with o- and m-dinitrobenzenes both nitro groups were hydrogenated.140 Reduction by sodium borohydride and Pd-C in methanol also does not appear to be selective, as 1,2,4-triaminobenzene is formed.141 It is of interest that over Pt-C in acidic alcohol 2,4-dinitroaniline is selectively hydrogenated at the 4-nitro group to give 4-amino-2-nitroaniline in 70% yield.142... 

One such epidioxypiperazinedione has been reduced to a regular pyrazine. Thus l,4-dibenzyl-2,3-dioxa-5,7-diazabicyclo[2.2.2]octane-6,8-dione (86) underwent reduction by sodium borohydride in ethanol at 20°C during 1 h to afford 3,6-dibenzyl-3,6-dihydroxy-3,6-dihydro-2,5( l//, 4//)-pyrazincdione (86a) in 65% yield, confirmed in structure by dehydration to 3,6-dibenzylidene-3,6-dihydro-2,5(1 H, 4//)-pyrazincdionc (86b).5... 

The other applications are mercury reduction by sodium borohydride (NaBH4) and lead reduction by alkali metal hydride (MH). 

The oxidation of bound hydroxyproline (CLII) to a 4-ketoproline peptide (CLIII), reduction by sodium borohydride to the allohydroxyproline peptide (CLIV), and the action of acid might lead to cleavage (CLV-CLVII)... 

CarbocycUc Steroids.— The Torgov synthesis continues to exhibit its great versatility and was recently employed in the first synthesis of B-homo-oestrone. Condensation of the vinyl alcohol (407) and 2-methy 1-cyclopentane-l,3-dione in the presence of l,4-diazabicyclo[2,2 ]octane and cyclisation with toluene-p-sulphonic acid gave the B-homo-oestrapentaene (409) in 33 % overall yield from 3-methoxybenzosuberone. A three-stage reduction by sodium borohydride, catalytic hydrogenation, and lithium-ammonia afforded 3-methoxy-B-homo-... 

Some years ago, Malmstrom etal. synthesized water-soluble metal phosphine complexes based on water-soluble polymers [41], In order to have solubility in both an acidic and a basic medium, they prepared two different water-soluble polymers. For the first, they made methyl [4-(diphenylphosphino)benzyl]amine (PNH) react with poly(acrylic acid) (PAA) using dicydocarbodiimide (DCC) as the coupling agent, under strict exclusion of oxygen (25). For the second, they reacted (4-carboxy-phenyl)diphenylphosphine with polyethylene imine (PEI) at room temperature (26). The reduction by sodium borohydride was made in situ, followed by the addition of methanesulfonic add and diethyl ether. Then, the methanesulfonic salt of phosphinated polyethylenimine was predpitated. 

The reduction by sodium borohydride in the presence of trifluoroacetic acid90 9 has also been applied to pyrido[2,3-6]pyrazine (9).92... 

The amidine reduction by sodium borohydride is efficient, although longer reaction times (up to 15 hr) may be required depending on the amine used. The mode of decomposition of the intermediate geminal diamine is known to favor preferential expulsion of the less basic amine leaving group.5 In fact, the alkylated amine was obtained with a selectivity higher than 80% (up to 99%) with all the compounds the submitters tested (see Table I). 

We focus first on the inherent reactivity of the carbonyl compound itself. An irreversible processes in which the addition product is stable is the most direct means of comparing the reactivity of carbonyl compounds. In these circumstances, the relative rate of reaction of different carbonyl compounds can be directly compared. One such reaction is hydride reduction. In particular, reductions by sodium borohydride in protic... 

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