Resonance borohydride proton

It has also been possible to confirm the presence of the reduction product of a Schiff base on the polymer by proton magnetic resonance. For this purpose we have used unmodified poly(ethylenimine), since it too catalyzes the decarboxylation of oxalacetate to its product, pyruvate. Unmodified polyethylenimine was mixed with oxalacetate-4-ethyl ester. One-half of this solution was treated with NaBH4 the second half was exposed to a similar environment but no NaBH4 was added. The borohydride-treated polymer exhibited a strong triplet in the nmr spectrum centered at 3.4 ppm upfield from the HOD resonance. This new feature would be expected from the terminal methyl protons of the oxalacetate ester attached to the polymer. Only a very weak triplet was found in the control sample not treated with borohydride. These observations are strong evidence for the formation of Schiff bases with the polymer primary amine groups. Evidently the mechanistic pathway for decarboxylation by the polymer catalyst is similar to that used enzymatically. 

The direct attack of proton from the solvent on the intermediate dihydropyridine as well as the over-all mechanism of the reduction received support from the extent and position of deuterium labeling in the product from the reduction of l-methyl-4-phenyl-pyridinium iodide (7) with sodium borohydride in dimethylformamide and deuterium oxide. The l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (9) formed was shown by nuclear magnetic resonance (NMR) and mass spectral analysis to contain approximately one deuterium atom located at the 3-position.13,14 This is the result to be expected from the pathway shown in Eq. (3) if the electrophile were a deuteron. 

Treatment of aqueous solutions of bis(ethylenediamine)dichloro-rhodium(III) with sodium borohydride give solutions which the proton magnetic resonance spectrum shows to contain an Rh—H complex (t 31 p.p.m., J Rh—h 31 c.p.s.). Also, the infrared spectrum of the precipitated tetraphenyl boronate shows a band at 2100 cm-1 assigned to an Rh—H stretch. 

We have developed a new synthesis of metal formyl compounds from the addition of metal trialkoxyborohydrides to metal carbonyls (10,11). The formyl proton characteristically appears at very low field, 14-16 8, in the NMR spectrum of metal formyl complexes. This low field resonance has allowed us to rapidly survey the reactions of trialkoxyborohydrides with a series of metal carbonyls. Initially, Na HB(OCH3)3 was used as the borohydride reducing agent, but we have subsequently found that K HB(0-i Pr)3" is a more rapid and eflFective hydride donor (JO). We have obtained NMR evidence for the formation of metal formyl complexes in the reactions of K HB(O-f-Pr)3" with Fe(CO)5 (14.9 8) (C6H50)3PFe(C0)4 (14.8 8, d, / = 44) (C6H5)3PFe(CO)4 (15.5 8, d, / = 24) Cr(CO)6 (15.2 8) W(CO)e 5.9 8) and Re2(CO)io (16.0 8). In some cases we have isolated the metal formyl complexes. In other cases, such a Cr(CO)6, the maximum observed conversion to (CO)5Cr-CHO was 76% after 25 min at room temperature, and the formyl complex underwent subsequent decomposition with a half-life of 40 min at room temperature. 

Bumamicine. This natural constituent isolated in trace quantities from Hmteria eburnea is included here because of its obvious relationship to corynantheol and because it represents a good example of the use of mass spectrometry in structure deduction. Bumamicine had an ultraviolet absorption maximum typical of a 2-acylindole which changed to that of a typical indole upon either sodium borohydride reduction or solution in acid. After the latter experiment the original chromophore was regenerated in basic solution. From the nuclear magnetic resonance spectrum the four aromatic protons, the ethylidene and the N-methyl were identifiable. The recovered alkaloid upon acetylation had an ultraviolet and nuclear magnetic resonance spectrum consistent for an ind N,0-diacetate (probably primary). 

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