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 β‐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 β‐carboline 5. Subsequent reactions performed on the β‐carboline 5 led to the formation of canthine and canthin‐6‐one derivatives. These syntheses both involved methyl 1‐formyl‐β‐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 underwent oxidative deamidation to afford cyclopenta[b]indole‐2,3‐dione (37), while substitution by alcohols afforded the alkoxy derivatives 40 and 41. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)