3,4-Dihydro-Β-Carbolines: II. THE EXHAUSTIVE METHYLATION OF 3,4-Dihydro-Β-Carboline

Abstract

The n~ethiodide of 3,4-dihydro-0-carboline yields a dimeric anhydro base which, on heating, disproportionates to a 0-carboline and a tetrahydro-p-carboline derivative, and on nlethylation is co11verted to 3-[3-forrnylindolyl]-~-ethyltrin1ethylan1111oni~n iodide.Although a large number of 1-substituted 3,4-dihydro-@-carbolines have beell synthesized (1, 2), the parent base itself (11, R=H) has not been well characterized. 3,4-Dihydro-P-carboline was first obtained (3) by degradation of evodiainine. I t was isolated a s a tarry mass, which yielded a picrate, and was identified by oxidation to Pcarboline (4). Atteinptecl synthesis by conventioiial Bischler-Napieralslti ring closure of NB-forii~~7ltryptarnine (I, R = H ) gave an uiicharacterized product in 2y0 yield (2). The base was later obtained by this inethod in 36y0 yield as an amorphous powder of indeterminate melting point, yielding a picrate and a perchlorate (5).Crude 3,4-dihydro-p-carboline (11, R = H ) has now been obtained in SOY0 yield froill NB-forniyltryptarnine (I, R = H ) , using polyphosphoric acid as the dehydrating agent. The conipound resisted purification because of its sensitivity towards aqueous acid and its tendency to polymerization. Analysis of the free base was unsatisfactory. The inethiodide, however, showed the expected composition. 9-Methyl-3,4-dihydro-P-carboline (11, R = CHJ, obtained from N8-for~nyl-1-inethyltryptamine (I, R = CH3), behaved similarly. The ultraviolet absorption curves of both compounds (Fig. 1) were similar to those of 1-alkyl-3,4-dihydro-P-carbolines (6), and the infrared spectra were also consistent with the assigned structure.