Borohydride reduction, table

Pt/C, PtSn/C and PtSnCu/C electrocatalysts were prepared by borohydride reduction (Table 1). 

Sodium borohydride reductions of gold(I) complexes give Au clusters at RT if sodium borohydride in ethanol is dropped slowly into a suspension of the Au(I) complex in the same solvent. The immediate coloring of the reaction mixture (mostly red), even after only a few drops of the borohydride have been added, indicates fast formation of Au clusters. In view of the complicated composition of these compounds the fast formation is surprising. The use of H2 and CO with HjO as reducing agents in the synthesis of gold clusters has been described (see Table 1, Method A, 8.2.2.2). 

Potassium borohydride reduction of runanine (17) yielded dihydro-runanine (24), the H-NMR spectrum of which (Table II) exhibited a triplet (64.25), the proton bearing the hydroxyl group coupling with those of C-5 (35). The optical activity of runanine (17), [a]D —400°, was similar to that of hasubanonine (5), [a]D —214° (3) therefore, it was concluded that the ethylamine linkage must have the same configuration as hasubanonine [C-13 (R) and C-14 (S)]. From these results, structure 17 was proposed for runanine (35) however, no application of mass spectral data to the structure elucidation was presented (35). 

In order to determine whether or not added steric effects in using a-methylbenzyl contributed to the induction of R configuration in the sodium borohydride reduction, the same sequence of reactions was carried out employing RS-a-methylbenzylamine. Analysis of the products from both reaction sequences gave the results summarized in Table 2. 

TABLE 9.4 Hydrogenation of Nitrobenzene over Platinum Metal Catalysts Produced In Situ by Borohydride Reduction 2 ... 

This is a common method for preparing transition-metal hydrides (see Table I) " . Borohydride reduction is complex, e.g., RujfCOjj with NaBH in THF gives over a dozen products, but a few useful mechanistic generalizations can be offered. Syntheses of metal hydrides proceed through intermediate borohydride complexes. Electron-pair bases (an ethereal solvent may be sufficient) are then necessary to complex and remove BHj. In a few examples the borohydride complexes are observable ... 

EPA. 1997b. Method 7742 Selenium (Atomic absorption, borohydride reduction). In Status tables for SW-846, third edition. U.S. Environmental Protection Agency. 

Comparable results were obtained from a structural study of a wheat-starch dextrin. The major fraction from aqueous ethanol solution (37%) was purified by acetylation, and then the deacetylated product was subjected to (a) methylation and hydrolysis, and (6) periodate oxidation, sodium borohydride reduction, and hydrolysis. Both procedures indicated a chain-length of about 8 D-glucose residues. Furthermore, the methylation products were identical with those in Table II, again showing the highly branched structure of the dextrin. 

The stereoselectivity of the hydride reduction of conjugated cyclohexenones has also been subjected to close examination from both experimental and theoretical viewpoints. Much of the work has involved polycyclic systems, e.g.. steroids which have little conformational flexibility and in which axial and equatorial directions of approach can be clearly defined. With small" hydride donors, these substrates show an even clearer preference for axial attack than the corresponding cyclohexanones. For examples involving reductions with lithium aluminum hydride and sodium borohydride, see Table 10. 3/(-Acetylcholest-5-en-7-one and cholest-2-en-l-one are notable in that the analogous saturated substrates are attacked from the equatorial direction115 l16. The reduction of 17/i-hydroxy-4-androsten-3-one (testosterone) to 4-androstene-3/1,17/j-diol with d.r. 90 10 can be compared with the sodium borohydride reduction of 17/i-hy-droxyandrostan-3-one (dihydrotestosterone) to androstane-3/ ,17/ -diol with d.r. 81 19 (see p 4030). 

Saito and co-workers isolated an alkaloid from the roots of Securinega virosa which they originally called virosine 53). It was later renamed dihydronorsecurinine to avoid confusion (see footnote e, in Table I) 61). Dihydronorsecurinine was shown to be identical with the sodium borohydride reduction product of norsecurinine (Section III, A). Since the absolute configuration of the latter has been established, the structure and absolute stereochemistry of dihydronorsecurinine is fully represented by formula 165a (Scheme 27) 62). 

One of the most attractive features of borohydride reductions is that under microwave-enhanced conditions they can be performed in the solid state, and rapidly. We were attracted by the work of Loupy et al. [71], and in particular Varma and Saini [72, 73] who have shown that irradiation of a number of aldehydes and ketones in a microwave oven in the presence of alumina doped NaBH4 for short periods of time, led to rapid reduction (0.5-2 min) in good yields (62-93%). In our study [74], seven aldehydes and four ketones were reduced (Table 18.3). Again reduction was complete within 1 min, the products were of high purity (>95%) and of high isotopic incorporation (95%, same as the NaBD4), and the reactions completely selective. 

The first two entries in Table 23.2 illustrate reactions that involve nucleophilic addition to the carbonyl group of the open-chain form which, although present in small amounts, is continuously replenished as it reacts. Entry 1 is the sodium borohydride reduction of the carbonyl group of the aldose o-galactose. The reaction is a general one other... 

Table I. Product distribution from borohydride reduction of 3 mercurated cyclic peroxides.

A large number of sodium borohydride reductions have been performed and some of the results appear in Table 3. After careful evaluation, the solvent of choice was 1,2 dichloroethane to which... 

Table 3. Sodium Borohydride Reductions of Ketones in 1,2-dichloroethane (Note 1)...

The structure of batrachotoxin was confirmed by a partial synthesis from batrachotoxinin A. This proved feasible using a mixed anhydride prepared from 2,4-dimethylpyrrole-3-carboxylic acid and ethyl chlorofor-mate (Scheme I). A variety of analogs of batrachotoxin were prepared in a similar manner. These compounds are documented in Table 4. A dihydro-batrachotoxin was prepared by sodium borohydride reduction (Scheme II) and apparently is subject to allylic rearrangement to other dihydroproducts 251). 

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