Reactivity of β-carbolines and cyclopenta[b]indolones prepared from the intramolecular cyclization of 5(4H)-oxazolones derived from L-tryptophan

4-(1H-Indol-3-ylmethyl) -2-trichloromethyl-1,3-oxazol-5(4H)-one (4) was shown to undergo an intramolecular reaction in the presence of TFA, to afford a beta-carboline 5 and a cyclopenta[b]indolone 6 by nucleophilic addition at C-2 and C-5, respectively. The distribution of these two products was found to be dependent on the reaction temperature, with lower temperatures favouring the formation of the beta-carboline 5. Subsequent reactions performed on the beta-carboline 5 led to the formation of canthine and canthin-6-one derivatives. These syntheses both involved methyl 1-formyl-beta-carboline-3-carboxylate (20), a useful precursor which was prepared in 54% yield, by a four-step procedure, from readily available L-tryptophan. The cyclopenta[b]indolone 6 readily under-went oxidative deamidation to afford cyclopenta[b]indole-2,3-dione (37), while substitution by alcohols afforded the alkoxy derivatives 40 and 41. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).