Emde degradation

A (ies-base, C22H2gON2, m.p. 143-4 , des-base-A, identical with (4) from the Emde degradation of a methylstrychnidinium salt (see above). Formula (XV) for dfi5-base-A has been modified recently the ethylenic linkage is now placed at —C instead of at... 

The Hofmann and Emde degradation of tetrahydro-j8-carboline derivatives has been reported in a number of instances, but only in one... 

Acid-catalyzed hydrolysis of the latter followed by Jones oxidation furnished racemic peshawarine (43) (Scheme 12). Simanek et al. (59) transformed the same amino acetal 47, obtained in optically active form from the Emde degradation of rhoeadine methiodide (48), to ( )-43, also by hydrolysis and oxidation. However, the optical activity was lost during hydrolysis (Scheme 12). 

Several syntheses of peshawarinediol (44) were carried out. The dex-trarotatory enantiomer was synthesized by a Czech group (57-59) from both rhoeagenine methiodide (45) and rhoeageninediol methiodide (51) by Emde degradation (Scheme 11). The same reaction performed on isorhoeageninediol resulted in (—)-44 (58,61). Racemic peshawarinediol (44) was synthesized (52) in way similar to that of ( )-43 by using urethane 52 and dithian 26... 

Several syntheses of secoquettamines have been performed. Seco compounds 234 and 235 were semisynthesized from quettamine (236) by Hofmann and Emde degradations, respectively (179). Chattopadhyay and Shamma (184) conducted a total synthesis of these bases with the intermediacy of quettamine (236) (Scheme 36). In this approach Reissert compound 237 served as substrate. On reaction with 4-benzyloxybenzaldehyde 237 supplied the addition product 238, which after N-methylation and sodium borohydride reduction afforded amino carbinol 239. Compound 239 was cyclized to... 

Tetramethoxydehydrolaudanosoline iodide (14), now named 0-methylcryp-taustoline iodide, was used in Hofmann and Emde degradations (Scheme 3). The... 

Scheme 3. Emde degradation of 0-methylcryptaustoline iodide by Robinson.

EMDE DEGRADATION. Modification of the Hofmann degradation method for reductive cleavage of the carbon-nitrogen bond by treatment of an alcoholic or aqueous solution of a quaternary ammonium halide with sodium amalgam. Also used as a catalytic method with palladium and platinum catalysts. The method succeeds with ring compounds not degraded by the Hofmann procedure. 

Methylation of the phenolic OH in the product of Emde degradation decinine (32) with trimethylanilinium hydroxide (24) resulted in cleavage the lactone ring to yield derivative 33. 

The lactone ring in decinine (2) was reduced to the cyclic ether (34) with diborane generated from sodium borohydride and boron trifluoride. The Emde degradation of (34) afforded a piperidine derivative (35a). The Cyanogen bromide N-demethylation of the methyl ether (35b) followed by... 

Finally, one has to mention the work of Levy and co-workers who described the semi-synthesis of D-ring seco-rhazinilam analogues from (-)-tabersonine using an Emde degradation and /nCPBA oxidation [90]. The. veco-analogue 50 is only twice less active than rhazinilam on the inhibition of microtubules disassembly, illustrating that the absence of the D-ring is not strictly deleterious to the antitubulin activity [91,92]. 

The application of the Emde degradation conditions (0.1 N KOH/C2H5OH, H2/Pt) to the quaternary curare alkaloid, mavacurine iodide (VIII/94), led to the so-called e2-dihydromavacurine (VIII/95), a tertiary base, Scheme III/18. Protonation (e.g. HC1/H20) or methylation (CH3I) of VIII/95 led to the trans-annular reaction products, VIII/96 and VIII/97, respectively. The quaternary compound, VIII/96, returns to tertiary VIII/95 (reversible Hofmann elimination) in the presence of base or on tic (silica gel) [55]. 

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). 

The Hofmann and Emde degradations led to many interesting transformations, none of which, however, helped to shed light on the structural problem. 

The Emde degradation of tylophorine methiodide yields a product identical with that obtained from tylophorineisomethiodide. When tylo-phorinemethine is submitted to the Emde degradation, a compound, C26H33O4N (mp 155°-156°), is obtained which may be formulated as IX. 

Emde degradation The Emde degradation consists in treating a quaternary halide in alcoholic or aqueous solution with sodium amalgam. The quaternary chloride (la) in the Emde degradation affords the same product (2) as is obtained by the Hofmann degradation of the quaternary base (lb). Further degradation of (3) by... 

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