Sodium borohydride-Palladium charcoal

The partial reduction of the nitro group to the hydroxylamine function in ethyl (V-(3-nitro-2-pyridyl)oxamate 1 by sodium borohydride/palladium on charcoal in aqueous sodium hydroxide and ensuing cyclization affords the corresponding 1 -hydroxypyrido[2,3-b]pyrazine-2,3(1//,4//)-dione 2.6... 

Dibenz[/>,e]azepines, e.g. 15, are reduced readily to the 5,6-dihydro derivatives, e.g. 16, with hydrogen and palladium on charcoal, or Raney nickel, at room temperature,28,104 with sodium in ethanol,104 with sodium borohydride in methanol,104 and with lithium aluminum hydride in diethyl ether.115... 

Reduction of 2,2-bisf3 -nltro-4 -(4"-phenylsulfonylphenoxyl)phenyl1 propane. Compound 9, 200 mg (0.55 meg) was dissolved in a mixture of 30 mL of dichloromethane (DCM) and 30 mL of methanol and 240 mg of 10% palladium on charcoal was added. After purging the solution with argon for 30 min, 520 mg (13.6 mmol) of sodium borohydride was added portionwise over 10 min. The reaction mixture was stirred under argon for 1 hr before addition of 30 mL of DCM. The mixture was filtered, the filtrate evaporated, and the residue extracted with DCM. Evaporation of the extract yielded 140 mg (76.2%) of 2,2-... 

Palladium catalysts resemble closely the platinum catalysts. Palladium oxide (PdO) is prepared from palladium chloride and sodium nitrate by fusion at 575-600° [29,30]. Elemental palladium is obtained by reduction of palladium chloride with sodium borohydride [27, 31], Supported palladium catalysts are prepared with the contents of 5% or 10% of palladium on charcoal, calcium carbonate and barium sulfate [32], Sometimes a special support can increase the selectivity of palladium. Palladium on strontium carbonate (2%) was successfully used for reduction of just y, (5-double bond in a system of oc, / , y, (5-unsaturated ketone [ii]. 

Hydrogenation using Raney nickel is carried out under mild conditions and gives cis alkenes from internal alkynes in yields ranging from 50 to 100% [356, 357, 358, 359, 360]. Half hydrogenation of alkynes was also achieved over nickel prepared by reduction of nickel acetate with sodium borohydride (P-2 nickel, nickel boride) [349,361,362] or by reduction with sodium hydride [49], or by reduction of nickel bromide with potassium-graphite [363]. Other catalysts are palladium on charcoal [364], on barium sulfate [365, 366], on... 

On rare occasions the aldehyde group in an a,/l-unsaturated aromatic aldehyde was reduced to a methyl group. 6-Benzyloxyindole-3-carboxaldehyde was transformed to 6-benzyloxy-3-methylindole by sodium borohydride in isopropyl alcohol in the presence of 70% palladium on charcoal (yield 89%) [784]. 

A very short and elegant synthesis of the 16-rtiembered dilactone ( )-pyrenophorin (515) has been accomplished by the dipolar cycloaddition reaction of a trialkylsilyl nitronate (81TL735). Nitromethane was added to 3-buten-2-one and the carbonyl group of the product reduced with sodium borohydride. The nitro alcohol (511) was converted to the acrylate (512) which was then subjected to a dimerization-cyclization reaction by treatment with chlorotrimethylsilane and triethylamine in dry benzene. Hydrogenation of the mixture of isoxazoline products (513) over palladium on charcoal followed by double dehydration of the intermediate bis-/3-hydroxyketone (514) led to ( )- and meso-pyrenophorin (Scheme... 

Note. (1) Addition of the reagents in this order prevents the possible ignition of hydrogen which can take place on addition of dry palladium-charcoal to solutions of sodium borohydride. 

The C5 aldehyde intermediate is produced from butadiene via catalytic oxidative acetoxylation followed by rhodium-catalyzed hydroformylation (see Fig. 2.30). Two variations on this theme have been described. In the Hoffmann-La-Roche process a mixture of butadiene, acetic acid and air is passed over a palladium/tellurium catalyst. The product is a mixture of cis- and frans-l,4-diacetoxy-2-butene. The latter is then subjected to hydroformylation with a conventional catalyst, RhH(CO)(Ph3P)3, that has been pretreated with sodium borohydride. When the aldehyde product is heated with a catalytic amount of p-toluenesulphonic acid, acetic acid is eliminated to form an unsaturated aldehyde. Treatment with a palladium-on-charcoal catalyst causes the double bond to isomerize, forming the desired Cs-aldehyde intermediate. 

While the condensation of enamine 37 with methyl OY7 s-2-butenoate, followed by acid hydrolysis and sodium borohydride reduction affords lactone 38 with reasonable efficiency, the cyclodehydrative ring contraction of this intermediate with PPA gives a mixture of bicyclo[3.3.0]octenones in abysmal (< 5 %) yield.66 To circumvent this difficulty and enable the large scale production of 39,2-carbo-methoxy-4,4-dimethylcyclohexanone was initially transformed to tram diacid 40 under Favoiskii conditions (Scheme 14). Conversion to the diacid chloride and condensation with lithium dimethylcuprate resulted in formation of the diacetyl derivative. In basic solution, the latter is reported to experience epimerization and aldol cyclization with dehydration in 82 % yield. With hydrogen and palladium on charcoal, the essentially quantitative production of 39 was achieved.66 ... 

NaBHi-Pd-C. Aromatic nitro compounds are not normally reduced by NaBHi but can be reduced smoothly in solution in water or methanol with sodium borohydride catalyzed by 10% palladium charcoal. Azobenzene is reduced by this method to hydrazobenzene and not to aniline. 

In an attempt to prepare cyclic hydroxylamines Coutts et al. (76CJC993) (Scheme 108) reduced an aqueous alkaline solution of 4-[(2-nitrophenyl)thio]pyrazol-3-ones 385a,b with sodium borohydride in the presence of 10% palladium-on-charcoal. The products were a mixture of spiro[l,3-benzothiazole-2,4 -pyrazol]-3 -ones 390a,b and... 

A different reduction was employed by Coutts et al. on (t-(2-nitrophenylthio) esters to give hydroxamic acid derivatives (84), sodium borohydride with palladium-charcoal being used to effect the cyclization.128... 

Coutts et al. unsuccessfully attempted to prepare benzothiazines by reductive cyclization of /J-keto sulfides with sodium borohydride or palladium-charcoal. They isolated only the/ -(2-nitrophenylthio) alcohols,136 in contrast to the successful synthesis of the desired ring by the same reduction of /J-(2-nitrophenylthio) esters.128 A wide range of /3-keto sulfides has been successfully reduced to dihydro-1,4-benzothiazines, using tin and hydrochloric acid, in either glacial acetic acid or ether solution.21... 

Hydrogenation of tetrazolo[l,5-6][l,2,4]triazines 6 with a palladium on charcoal catalyst stopped after the absorption of 1 molar equivalent of hydrogen and the 7,8-dihydro derivative was isolated. Reduction of the same compounds with sodium borohydride in methanol produces the corresponding 5,6,7,8-letrahydro compounds.376... 

The reductive animation of 3-oxo-l,2.3.4-tetrahydrocarbazole with (S)-phenylethylamine and sodium borohydride leads to (37 )-3-[(l.S )-phenylethylamino]-l,2,3,4-tetrahydrocarbazole in 39.7% yield. The cleavage of the phenylethyl group is accomplished by a transfer hydrogenation, with ammonium formate as a hydrogen donor and palladium on charcoal as a catalyst, to give the enantiomerically pure (3/ )-3-amino-l,2,3,4-tetrahydrocarbazole23. 

The reduction of 4-[(2-nitrophenyl)methylidene]pyrazol-3-ones 487a,b by sodium borohydride and 10% palladium-on-charcoal in 1,4-dioxane followed by acetic acid treatment, afforded mixtures containing spiroindolepyrazol-3-ones 489a,b and 4-(2-aminobenzyl)pyrazol-3-ones 490a,b (75CJC3645) (Scheme 150). A plausible explanation for the formation of derivatives 489 is concomitant reduction of the... 

Perhaps the most reliable method for the reductive cyclization of a nitro ester to a hydroxamic acid is that which involves treatment with sodium borohydride in the presence of palladium on charcoal. Although under these conditions aromatic nitro compounds are reduced to amines, o-nitro esters such as 53, in which the ester group is suitably oriented with respect to the nitro group, give good yields of cyclic hydroxamic acids (54). Coutts and his co-... 

JV-Alkylanthranilium salts, like their parent anthranils, are readily reduced to 2-alkylaminoacylbenzenes. Sodium dithionite,236,237 zinc,237 or iron in acetic acid,238 and palladium charcoal and hydrogen238,239 are the usual reducing agents. Reduction with sodium borohydride produces the synthetically useful benzisoxazolines (170) in high yield233,237 (see Section III,G,1). 

Partial reduction of the nitro group in compounds 69 with either sodium borohydride or hydrogen over a catalyst of palladium on charcoal results in the l-hydroxy-2-oxo compounds 70. °... 

The piperidine was prepared from 2-(2-cyanoethyl)-butryraldehyde (470) via ketal 471, which was reduced with lithium aluminum hydride and reductively alkylated with benzaldehyde over 10% palladium on charcoal to 472. Acid hydrolysis led to spontaneous cyclization and formation of enamine 473. Treatment of this enamine with methyl bromoacetate and reduction of the iminium species with sodium borohydride gave the 1-benzyl-3,3-disubstituted piperidine 474 which was debenzylated with palladium charcoal under acidic conditions to give the desired piperidine, 466 (216). 

Cyanopyridines have been reduced to aminoethylpyridines by a variety of methods, 2- And 4-cyanopyridine are reduced with sodium borohydride to 2-and 4-aminomethylpyridine, respectively. In acidic solutions, the polaro-graphic reduction of 4-cyanopyridine yields 4-aminomethylpyridine. Hydrogenation of 6-chloro-5-cyano-4-methoxymethyl-3-nitro-2-picoline over palladium-charcoal in aqueous hydrochloric acid gives 3-amino-5-aminomethyl-4-methoxymethyl-2-picoline hydrochloride. 3-Amino-5-aminomethyl-2,4-lutidine is prepared in good yield by the catalytic reduction (Pd—C in methanol) of 6-chloro-3-cyano-2,4-dimethyl-3-nitropyri-dine. The hydrogenation of 3-( S-pyridylmethoxy)propionitrile over Raney Nickel yields 3-[(3-aminopropoxy)methyl] pyridine. ... 

---