Palladium dehydrogenation

In a recent variation of this synthesis of the tetrahydro-j8-carboline system, hexahydro derivatives (65) of the salt 55 were cyclized to fully aromatic j8-carbohne derivatives (66a and 66b) on palladium dehydrogenation, presumably by way of an enamine intermediate. ... 

Palladium dehydrogenation of l,2,3,4-tetrahydro-j8-carboline-3-carboxylic acid or its ethyl ester has been reported to take place with loss of the carboxyl or carbethoxyl group, yielding j3-carboline. On the other hand, it has been reported that palladium dehydrogenation of either 1-methyl-1,2,3,4-tetrahydro-j8-carboline-3-carboxylic acid or 1,3-dicarboxyhc acid yields l-methyl-3,4-dihydro-j8-carbohne-3-carboxyhc acid and not l-methyl-jS-carboline. ... 

Palladium dehydrogenation of the hexahydro-jS-carboline derivative dihydrodesoxyajmaline (381) yielded, among other degradation products which included fully aromatic )3-carboline derivatives, the two substituted indoles 382 and 383. ... 

Pictet-Spengler synthesis is another method of preparing isoquinolines. (3-phenylethylamine reacts with an aldehyde to produce an imine, which undergoes acid-catalysed cyclization, resulting in the synthesis of the tetrahydroisoquinoline system. Again, tetrahydroisoquinoline can he aromatized hy palladium dehydrogenation to produce an isoquinoline system. 

The final ring closure again paralleled the olivacine synthesis passing through the intermediate jV-formyl rather than the V-acetyl, amine, to give 1,2-dihydroellipticine (CCXCIII) from which ellipticine was obtained by palladium dehydrogenation (160a). 

Palladium dehydrogenation of the base C16H24O2N2 (CCLXXXIX) leads to the formation of vomipyrine (CCXCVIII) and smaller quantities of base CCXCIX, shown to be an intermediate by being converted into vomipyrine by further treatment with palladium (188, 211). The structure of vomipyrine was proved by synthesis (212). 

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