Sodium borohydride-aqueous base

Sodium borohydride-aqueous base. Enone reduction. 2,6-Di-t-butyl- Formation of aryl radicals. Redn intermediates. Addition to a side-chain 6 Organotelluride anions. Ditellun are useful for phenylseleno removal front... 

In this section, details of an easily controllable, safe method for producing high-purity H2 gas are described. This method of generating H2 gas is particularly suitable for providing a clean source of H2 gas for use as an anodic fuel in fuel cells or as a fuel for internal combustion engines in transportation applications. This compact, portable H2 generator is based on a non-pressurized, aqueous solution of alkaline sodium borohydride (NaBH, tetrahydroborate). As found by Schlesinger et al.,1 when aqueous NaBH... 

Several replacement reactions at C-4 in sydnones may be carried out but aqueous bases must be avoided. Butyllithium can be used to displace bromine from a 3-phenylsydnone the resulting organolithium salt can be carbonylated, will add to ketones, and forms a silyl derivative (80CB1830). A sydnone Grignard derivative can also be made and will add ketones in the normal way (80JCS(Pl)20). Sodium borohydride will reduce a sydnone sulfone, formed by oxidation of a thioether (Table 5) with hydrogen peroxide, back to the unsubstituted sydnone (74T409). 

Another approach for the preparation of dendrimer-noble metal nanoparticles in toluene is a process driven by acid-base chemistry and ion pairing [35]. At first, palladium nanoparticles are prepared by reducing aqueous K2PdCl4 with sodium borohydride in the presence of G4 dendrimer where the pH of dendrimer solution is adjusted to about 2. The low pH protonates the exterior amines to a greater extent than the less basic interior tertiary amines. Accordingly, Pd2+ binds preferentially to the interior tertiary amines and upon reduction palladium particles form within the dendrimer interior. After the complete reduction, the pH of solutions is adjusted back to about 8.5. Then, these nanocomposites can be quantitatively transported from the aqueous phase into toluene containing 10-20% of dodecanoic acid. The transition is visualized by the color change brown aqueous solution of dendrimer-palladium nanoparticles becomes clear after addition of the acid, while the toluene layer turns brown. 

Mitsunobu reaction as well as by mesylation and subsequent base treatment failed, the secondary alcohol was inverted by oxidation with pyridinium dichromate and successive reduction with sodium borohydride. The inverted alcohol 454 was protected as an acetate and the acetonide was removed by acid treatment to enable conformational flexibility. Persilylation of triol 455 was succeeded by acetate cleavage with guanidine. Alcohol 456 was deprotonated to assist lactonization. Mild and short treatment with aqueous hydrogen fluoride allowed selective cleavage of the secondary silyl ether. Dehydration of the alcohol 457 was achieved by Tshugaejf vesLCtion. The final steps toward corianin (21) were deprotection of the tertiary alcohols of 458 and epoxidation with peracid. This alternative corianin synthesis needed 34 steps in 0.13% overall yield. 

A convenient method to affect the oxidation beta to nitrogen in piperidines is based upon the anodic oxidation of A-carboalkoxy piperidines. For example, the electrochemical oxidation of piperidine 108 in the presence of acetic acid and potassium acetate afforded a mixture of isomeric 2-hydroxy-3-acetoxypiperidines 109 in a combined yield of 93%, following an aqueous workup [32]. Reduction with sodium borohydride severed the C-OH bond. Treatment of the resulting acetate 110 with HBr followed by NaOH completed a straightforward synthesis of pseudoconhydrine (111) (Scheme 11). 

A Schiff base is a relatively labile bond that is readily reversible by hydrolysis in aqueous solution and can be chemically stabilized by reduction. The formation of a Schiff base is enhanced at alkaline pH values, but is still not entirely stable unless reduced to a secondary or tertiary amine linkage (Hermanson, 1995). The addition of sodium borohydride or sodium cyanoborohydride will result in reduction of the Schiff base intermediate into a relatively stable secondary amine. Both borohydride and cyanoborohydride have been used for reductive amina-tion purposes, but borohydride will simultaneously reduce the reactive aldehyde groups to hydroxyls and convert Schiff bases present to... 

Compound E has a prominent IR absorption at 1730 cm-1 and gives two singlet peaks in the H NMR spectrum. On reaction with sodium borohydride followed by aqueous acid, compound F is obtained. Compound F, which has a broad IR absorption at 3500-3200 cm-1, reacts with sodium hydride (a base) followed by methyl iodide to give compound G. The mass spectrum of G shows a molecular ion peak at m/z 102 and an intense peak at m/z 45. Propose the structures for compounds E-G. 

Various reactions of the 7-substitutent have been carried out, all of which have their counterparts in indole chemistry." Reduction of the imino compound 13, obtained from DMF-phosphoryl chloride treatment of 11 (R = Me), with potassium borohydride gave the Mannich base 14 (R = Me). Reduction of the aldehyde 12 (R = H) with sodium borohydride in the presence of aqueous dimethylamine gave the amine 14 (R = H), whereas the analogous aldehyde 12 (R = Me) gave only the alcohol 15 (R = Me)." The related alcohol 15 (R = H) was obtained on reducing the aldehyde with sodium borohydride in the absence of dimethylamine. ... 

On treatment of acomonine with potassium permanganate in aqueous acetone, an anhydro-oxy-derivative resulted. This internal carbinol amine ether was converted into the original base by sodium borohydride reduction. Permanganate oxidation of desoxyacomonine gave an oxo-derivative containing a y-lactam. On the basis of this chemical and additional spectral data, the secondary hydroxy-group was located at C-3. 

In reviewing the earlier chemical and spectral data, the presence of the epoxide moiety explains several observations. Excelsine is reduced with Raney nickel in methanolic base to lapaconidine (26), but is inert to reduction with Adams catalyst, sodium borohydride, or lithium aluminium hydride. Treatment of excelsine with boiling aqueous HCl gives an epimeric mixture of chlorohydrins. Hydrolysis with... 

Working with dehydroquinase isolated from E. coli 83-2, Butler et al. [119] demonstrated that the reaction was catalyzed via iminium ion formation, in a manner analogous with the model system shown in Scheme 19. They demonstrated that the enzyme was inhibited in the presence of both substrate and sodium borohydride. The inhibited enzyme did not regain activity upon dialysis. The enzymatic SYN elimination is contrasted with the non-enzymatic, base-catalyzed, trans-eUmination found in aqueous solution, in which the pro-S proton is stereo-selectively removed (Scheme 20). The stereochemistry of proton abstraction in the non-enzymatic case arises from the pro-S proton being in an axial position such that... 

The presence of the epoxide moiety at C-3 and C-4 in excelsine explained the interesting chemical reactions observed earlier. On treatment with acetic anhydride and p-toluenesulfonic acid, excelsine yielded a triacetate derivative, while treatment with acetyl chloride afforded a tetraacetate derivative. On reduction with Raney nickel in methanolic base, excelsine yielded lapaconidine (92), but was inert toward other reducing agents, e.g., lithium aluminum hydride, sodium borohydride, and Adams catalyst. Treatment of excelsine with boiling aqueous hydrochloric acid yielded an epimeric mixture of chlorohydrins with molecular formula C22H34NO6CI. These epimers were hydrolyzed to the crystalline compound C22H33NO6 when treated with aqueous sulfuric acid. This compound formed a tetraacetate derivative for which structure 105 was proposed on the basis of spectral data. 

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