Dehydrogenations with selenium

On the assumption that the two alkaloids may have a similar structure and, with that reservation, applying the result of the selenium dehydrogenation experiment to the case of solanocapsine, the authors suggest that the annexed formula (p. 670) aeeounts for all the reae ions of this alkaloid so far observed. 

Hi) Dehydrogenation. j3-Carboline derivatives may be obtained from tetrahydro-)3-carbohnes by zinc dust distillation or high temperatmre dehydrogenation with selenium or palladium black. Many of the complex indole alkaloids may be degraded, with bond cleavage, to yield simple )3-carbolines under these conditions and this approach has become a standard method in structural elucidations. Examples are numerous but outside the scope of this review. 

Recently Swan has employed tetrachloro-o-benzoquinone in the oxidation of the 3,4-dihydro-j8-carbolinium cation 124 to the j8-carbo-linium cation 252. Dehydrogenation with palladium black at 175° or at a higher temperature and with selenium has also been successfully used for the purpose. 

This ester cannot be dehydrogenated with palladium-charcoal, selenium, or chloranil 16 similar attempts to aromatize 4,5,6,7-tetrahydrobenzo[c]thiophene have failed.616 Diethyl 4,5,6,7-tetra-hydrobenzo[c]thiophene-l,3-dicarboxylate forms an adduct with maleic anhydride.6... 

These data indicate a close relationship with ajmalicine, which is supported by chemical evidence. Thus, selenium dehydrogenation gives alstyrine lithium aluminum hydride reduction gives a primary alcohol, akuammigol (I), which possesses a typical indole UV-spectrum, with a deep minimum at 250 m/r. The formulation of this product as an allylic alcohol, stereoisomeric with tetrahydroalstonol, is further shown by its... 

The presence of an ethylidene group in echitamine chloride was also demonstrated by oxidation with periodic acid, which was reported to give acetaldehyde and indole-3-acetaldehyde (78). Alkali fusion and selenium dehydrogenation experiments gave inconclusive results, but the basic fractions were suspected to contain derivatives of jS-carboline (77, 78). Oxidation of echitamine with alkaline potassium permanganate afforded a low-melting base, which was considered to be Nb-methyl-tryptamine (80). 

The only degradations that have so far been carried out with villal-stonine are the drastic ones of potash fusion and selenium dehydrogenation. Alkali fusion yields products characteristic of the indole alkaloids, namely, 2-methylindole, indole-2-carboxylic acid, and a basic fraction which exhibits a typical /3-carboline UV-spectrum a weak base also obtained in this degradation possesses a UV-spectrum closely resembling that of echitamidine. /3-Carboline derivatives, so far unidentified, also appear to be the products of selenium dehydrogenation (35). 

Dehydrogenation of cinchonamine with selenium or palladium-charcoal resulted in fission of the quinuclidine ring and the isolation of dehydrocinchonamine (V), mp 203°, whose spectral characteristics and p/fa were in agreement with its formulation. From the selenium dehydrogenation products, a trace of a crystalline compound was also obtained which, from a single ultimate analysis and UV-spectrum, is considered to be IV (10). 

Huntrabrine methochloride has an ethylidene group, a quaternary IV-methyl, a 5-hydroxyindole chromophore, and a primary hydroxyl group. It underwent a facile Emde degradation, and the resulting tertiary base upon tosylation gave a phenolic-O-tosylate quaternary tosylate. The latter compound, upon selenium dehydrogenation, afforded uncharacterized products, one with a sempervirine-like UV-spectrum and another with a 2-pyridylindole chromophore. All these results are interpreted as supporting the structure XLVI (see Table I) for huntrabrine methochloride (27). 

Selenium dehydrogenation of rauniticine gives alstyrine similarly obtained from ajmalicine. These alkaloids differ only in that raunitidine is a monomethoxyrauniticine. Their IR-spectra (3.4 p) indicates a C/D trans junction with the C-3-H axial. That the D/E junction is cis follows... 

The most puzzling of the Rauwoljia alkaloids is rauwolfinine, mp 235°-236°, [a]D — 35° (EtOH), which was first reported in 1954 (54) from a variety (Cochin) of R. serpentina and has been the subject of three additional papers (55) culminating in an analysis of its NMR-spectrum (56). Rauwolfinine was said to be an indoline alkaloid with one C methyl, and upon zinc dust or selenium dehydrogenation gave iV-methylharman. Rauwolfinine with 4 N sulfuric acid (55) was supposed to have afforded an indole [specifically, an indole aldehyde characterized as its 2,4-dinitro-... 

Sulfur and selenium react with many organic molecules. For example, saturated hydrocarbons are dehydrogenated. The reaction of sulfur with alkenes and other unsaturated hydrocarbons is of enormous technical importance hot sulfurization results in the vulcanization (formation of S bridges between carbon chains) of natural and synthetic rubbers. 

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