Sodium cyanoborohydride, and

Richter utilized a reductive amination in their synthesis of the natural product (+)-hapalindole Q [294], Employing 10 equivalents of sodium cyanoborohydride and 40 equivalents of ammonium acetate in a methanol/THF mixture (150 °C, 2 min), the primary amine was obtained as a 6 1 mixture of diastereomers. Transformation to the isothiocyanate completed the total synthesis of (+)-hapalindole Q (Scheme 6.150). 

Synthesis of a C(8)-C(18) segment of the larger fragment of lb using the same basic strategy is depicted in Scheme 25. Here, hydroxy ketone 176 was subjected to syn-selective (dr of crude product=90 10) reductive amination [42] with sodium cyanoborohydride and benzylamine followed by tetrahydro-oxazine formation using aqueous formaldehyde. The resulting heterocycle 182 was then converted to unsaturated ester 184 by successive desilylation, oxidation, and entirely (Z)-selective Horner-Wadsworth-Emmons olefination. Re-... 

The overall carbon-nitrogen framework was confirmed by synthesis. Reductive amination of the triketone (336) (429) with sodium cyanoborohydride and ammonium acetate formed a mixture of four isomeric pyrrolizidines. Pure sam-... 

Stractures of 3-alkyl-5-methylindolizidines, found in thief ants, Solenopsis species (Table II), arrived at by gas chromatographic and mass spectral analysis were confirmed by coinjection and direct comparison with the synthetic sample. Indolizidine 15a from S. conjurata exhibits characteristic peaks at miz 152 (M — CHj) and 138 (M — C2H5, a base peak) as well as a parent peak at m/z 167 in the mass spectram. It corresponds to an isomer of 3-ethyl-5-methylindolizidine (15) which was prepared as a mixture of four stereoisomers by reductive amination of triketone 391 with ammonium acetate-sodium cyanoborohydride and sodium borohydride (Scheme 47). 

Schkeryantz and Pearson (59) reported a total synthesis of ( )-crinane (298) using an intramolecular azide-alkene cycloaddition (Scheme 9.59). The allylic acetate 294 was first subjected to an Ireland-Claisen rearrangement followed by reduction to give alcohol 295, which was then converted into the azide 296 using Mitsunobu conditions. Intramolecular cycloaddition of the azide 296 in refluxing toluene followed by extrusion of nitrogen gave the imine 297 in quantitative yield. On reduction with sodium cyanoborohydride and subsequent reaction with... 

In the reductive animation method, it is important to use reagents and reactants of high purity. The carbohydrate sample should not contain carbohydrate contaminants, as, if they were present, an adsorbent containing more than one type of ligand would be obtained. The sodium cyanoborohydride should be of high purity, because reduction of the Schiff base may not occur with impure preparations. Special procedures have been developed for purifying sodium cyanoborohydride, and these should be employed.25... 

Dialkylpyrrolidines. These compounds can be prepared by reductive amination of 1,4-diketones with sodium cyanoborohydride and ammonium acetate (4, 448-449). 1-Pyrrolines are usually formed also, but they can be reduced to pyrrolidines by NaBH4 in a second step.1... 

Indolines are produced in good yield from 1-benzenesulfonylindoles by reduction with sodium cyanoborohydride in TFA at 0°C (Equation 5) (89TL6833). If acyl groups are present at C-2 or C-3 in the substrate, they are reduced to alkyl groups. Indole is also reduced to 2,3-dihydroindole by sodium cyanoborohydride and acetic acid or triethylamineborane and hydrochloric acid. An alternative method for preparing indolines involves treatment of indoles with formic acid (or a mixture of formic acid and ammonium formate) and a palladium catalyst (82S785). Reduction of the heterocyclic ring under acidic conditions probably involves initial 3-protonation followed by reaction with hydride ion. 

One of the starting materials, the bromoindolinemesylate 183 was obtained from the commercially available 5-hydroxyindole by mesylation followed by successive treatment of the resulting indole derivative with sodium cyanoborohydride and bromine. Coupling of 183 with the known boronic acid 184 in the presence of zero valent palladium complex led directly to the lactam 185, the intermediate carbinolamine 186 formed initially in the reaction suffering facile aerial oxidation during work-up. On reduction with sodium (2-methoxyethoxy)aluminium-hydride, the amide 185 yielded the aminophenol 187 which on chromatography underwent oxidative aromatisation to 182 in 54% yield. 

The principal component of the secretion of the poison gland of the European thief ant (Solenopsis fugax) is rrarcs-2-n-butyl-5-n-heptylpyrrolidine, identified by mass spectrometry and synthesis.5 The reductive amination of 1,4-diketones with sodium cyanoborohydride and ammonium acetate has yielded various 2,5-dialkyl-pyrrolidines that occur in the poison glands of ants of Monomorium spp.6... 

Inulin can be modified to compounds that display good heavy metal complexing properties similar to ethylene diamine tetra-acetic acid (EDTA) but with better biodegradation properties (Bogaert et al., 1998). Inulin is first oxidized using sodium periodate to the dialdehyde, and then reduced to a polyol using Pt/C and hydrogen. The polyol can then be modified with carbon disulfide to form xanthate or with S03-pyridine to obtain an inulin sulfate. Alternatively, the dialdehyde can be animated with diaminoethane and sodium cyanoborohydride and the product reacted with monochloroacetic acid sodium salt to form carboxymethylamino inulin. Each of these compounds can be used to precipitate heavy metals. 

The venomous constituent of the cryptic thief ant, Solenopsis xenovenenum, has been identified as the 3-heptyl-5-methylpyrrolizidine (50) from its mass spectrum and the fact that a related pyrrolidine (51) has been isolated from another species of ant.47 This is the first reported occurrence of a 3,5-dialkyl-pyrrolizidine, and its structure was confirmed by synthesis. Reductive amination of the known triketone (52) with sodium cyanoborohydride and ammonium acetate gave a mixture of four isomers of 3-heptyl-5-methylpyrrolizidine, which were separated by preparative g.l.c. The stereochemistry of the ring-junction of each isomer was established from its i.r. and n.m.r. spectra. 

Catalytic hydrogenation reduces the imine (as the protonated iminium ion) but not the ketone from which it is formed. This chemoselectivity (reduction of iminium ions but not ketones) is also displayed by sodium cyanoborohydride and we can add NaCNBH3 to complete our table of reactivity, if we insert imines at the left-hand end. 

During their synthesis of the Dactomelynes, Lee and co-workers employed sodium cyanoborohydride and titanium(IV) chloride95 to accomplish the regiose-lective cleavage of a benzylidene acetal [Scheme 3,57].%... 

Tosylhydrazones (260) of 3-oxo-steroids (and presumably of other suitable carbonyl derivatives) are reduced to saturated hydrocarbons (261) by sodium cyanoborohydride and toluene-p-sulphonic acid in dimethylformamide-sulpho-... 

Reduction of the double bond of vinylogous lactams 42 and 43 with sodium cyanoborohydride and subsequent hydrogenolysis of the resulting thioethers gave rise to the pwntacyclic ketones 44 and 45 as prepared by Biichi (71JA3299 75JA6880). The conversions of the pentacyclic ketones to vindrosine (46) and vindoline (47) involved a five-step sequence (Scheme 5). 

Selective reduction of aliphatic ketones and aldehydes to hydrocarbons,6 Aliphatic ketones and aldehydes can be reduced selectively in high yields to hydrocarbons with sodium cyanoborohydride and p-toluenesulfonylhydrazine in DMF-sulfolane containing p-toluenesulfonic acid at 100-105°. The prior preparation of tosylhydrazones is not necessary because carbonyl groups are reduced slowly by sodium cyanoborohydride. Maximum yields are obtained with a fourfold molar excess of NaBH3CN. Yields are in the range 62-98%. Ester groups, if present, are not affected. Aromatic ketones are not reduced. 

Benzaldoximes (4), obtained from the corresponding benzaldehyde and hydroxylamine, were selectively reduced to the hydroxylamine 5 with sodium cyanoborohydride by the procedure of Borch, Bernstein, and Durst (5). Upon scaling-up this reduction, we found it convenient to dissolve the oxime in methanol containing methyl orange as an indicator. Methanol solutions of sodium cyanoborohydride and hydrochloric acid were then added simultaneously with the rate of acid addition adjusted so as to maintain the red-orange transition point of the indicator. Yields were quite satisfactory, in the range of 60-80%. Reaction of the hydroxylamine with the malonyl dichloride gave the desired compounds (6). 

Several reducing agents have also been used for the reduction of (l-bromoalkyl)cyclopropanes, for example, hexaphenylditin, hydriodic acid, hydrogen over palladium on carbon, lithium aluminum hydride, ° lithium in the presence of terr-butyl alcohol, sodium borohydride, sodium cyanoborohydride, and tributyltin hydride. ... 

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