Sodium cyanoborohydride , combination

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

A valuable application of sodium cyanoborohydride is in the synthesis of amines by reductive amination. What combination of carbonyl and amine components would give the following amines by this method ... 

An interesting procedure has been proposed for the synthesis of amylose-b-PS block copolymers through the combination of anionic and enzymatic polymerization [131]. PS end-functionalized with primary amine or dimethylsilyl, -SiMe2H groups were prepared by anionic polymerization techniques, as shown in Scheme 56. The PS chains represented by the curved lines in Scheme 56 were further functionalized with maltoheptaose oligomer either through reductive amination (Scheme 57) or hydrosilyla-tion reactions (Scheme 58). In the first case sodium cyanoborohydride was used to couple the saccharide moiety with the PS primary amine group. 

Tertiary amine TV-oxides are rapidly deoxygenated by carbon disulphide1112. Oximes are reduced to primary amines by titanium(III) chloride in the presence of sodium cyanoborohydride, NaBTpCN1. The combined action of sodium borohydride and a chiral... 

A combined reductive amination sequence has been developed as a useful way of synthesizing amines, with sodium cyanoborohydride as the reducing agent of choice. This complex metal hydride is a less reactive version of sodium... 

Benzaldehyde (10.6 g) was added to a suspension of (+)-3-amino-6-carboxamido-l,2,3,4-tetrahydrocarbazole (12.35 g) in methanol (100 ml). The mixture was stirred for 1 h, sodium cyanoborohydride (9.3 g) added over 1 h and the clear solution stirred for 24 h. The solution was cooled (ice bath) and formaldehyde (37% aqueous methanolic, 9 1 solution, 5.5 ml) added. After 30 min stirring at room temperature water (100 ml) was added, stirring continued for 30 min followed by extraction with dichloromethane (3 times 150 ml). The combined organic extracts were washed with water (2 times 200 ml), dried (Na2S04), filtered and solvent removed at reduced pressure. The residue was column chromatographed (silica gel, dichloromethane-10% ethanol/dichloromethane) to give 3-N-benzyl-6-carboxamido-3-N-methylamino-l,2,3,4-tetrahydrocarbazole (9.4 g) as a foam. The succinate... 

Since sodium cyanoborohydride is a very mild reducing agent, (his method is particularly suitable for compounds containing reduciblegnoupssuchas COOH, COOR, CN, NOj, C=0. This method is thus more selective than the combination of sodium borohydride in DMF (3, 262). 

There have been two major approaches towards achieving selective reduction of carboxylic acid derivatives to aldehydes (or derivatives) by hydrides. Firstly, hydride reagents themselves have been modified as, for example, sodium borohydride and sodium cyanoborohydride. Sometimes these modifications have led to finely tuned reducing agents, as with the dimethyl sulfide adduct of thexylbromoborane (see later). Secondly, the type of carboxylic acid derivative has been modified for the optimum yield of aldehyde. For example, amides have been made from an assortment of amines in efforts to maximize yields of aldehyde. Best yields of aldehydes are obtained usually by a combination of modified hydride reagent with a modified carboxylic acid derivative. 

Reduction of the heterocyclic ring is readily achieved under acidic conditions formerly, metal-acid combinations were used, but now much milder conditions employ relatively acid-stable metal hydrides, such as sodium cyanoborohydride. Triethylsilane in trifluoroacetic acid is another convenient combination ... 

Reduction of the heterocyclic ring is readily achieved under acidic conditions formerly, metal-acid combinations were used, but now much milder conditions employ relatively acid-stable metal hydrides such as sodium cyanoborohydride. Triethylsilane in trifluoroacetic acid is another convenient combination 2,3-disubstituted indoles give cis indolines by this method. Such reductions proceed by hydride attack on the p-protonated indole - the 3//-indolium cation. Catalytic reduction of indole, again in acid solution, produces indoline initially, further slower reduction completing the saturation. ... 

If procainamide is reacted with dialdehydo-inulin in the presence of sodium cyanoborohydride polymer-drug combinations (VI) are formed which have the drug linked via a stable bond ... 

Regioselective ring opening of epoxides to the less-substituted alcohol, by hydride capture at the better potential carbenium ion centre, is achieved with a sodium cyanoborohydride-boron trifluoride combination anti ring opening is favoured. 

Cyanoborohydride and its modified reagents have been used for reductive dehalogenations. Thus, the combination of sodium or tetrabutylammonium cyanoborohydride, sodium or potassium 9-cyano-9-hydro-9-borabicyclo[3.3.1]nonanate [9-BBNCN] (2) or polymeric cyanoborane (3) in HMPA furnishes an efficient and mild system for the reduction of alkyl halides. The reagents are selective in that other functional groups, including ester, carboxylic acid, amide, cyano, alkene, nitro, sulfone, ketone, aldehyde and epoxide, are essentially inert under the reduction conditions thus, the reduction procedure is attractive for synthetic schemes which demand minimum damage to sensitive portions of the molecule. 

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