Reactivity of β‐Carbolines and Cyclopenta[b]indolones Prepared from the Intramolecular Cyclization of 5(4H)‐Oxazolones Derived from L‐Tryptophan

Abstract

Keywords: 5(4H)-Oxazolone / β-Carboline / Cyclopenta [b]indolone / Cyclization / BischlerϪNapieralski reaction / Canthine / Synthesis design 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.

Versatility of Substituted 1‐Formyl‐9H‐β‐carbolines for the Synthesis of New Fused β‐Carbolines via Intramolecular 1,3‐Dipolar Cycloaddition

“…[3] In their efforts to develop new route to canthines, Condie and Bergman have earlier reported the alkylation of methyl 1-formyl-9H-β-carboline carboxylate via allyl bromide in the presence of NaH in DMSO in high yields. [5] However in our hands the experiment did not work well and the desired compound was obtained in minor yields only. Consequently we decided to first install the allyl chain on NH of the β- carboline in 7-9 through allyl bromide and then deprotect the acetal functionality.…”

1-Formyl-9H-β-Carboline: A Useful Scaffold for Synthesizing Substituted- and Fused β-Carbolines

“…In a modified strategy, these workers reported the synthesis of methyl 1-formyl-9H--carboline-3-carboxylate derivatives (2 and 44), by a four-step procedure from readily available L-tryptophan derivatives [23]. The reaction proceeded through an oxazolone intermediate (43) carboline-3-carboxylates (2 and 44) as demonstrated in Scheme 13.…”

Synthesis of some fused β‐carbolines including the first example of the pyrrolo[3,2‐c]‐β‐carboline system

“…We have previously described the high yielding conversion of 1-dichloromethyl-β-carboline (7) to 1-formyl-βcarboline [9] (3 7), conducted under acidic conditions. Reduction of 37 with lithium aluminium hydride gave the diol 38 in moderate yield, whilst the subsequent oxidation with "very active manganese dioxide" consistently gave 39, but in only 58% yield.…”

“…yielding synthesis that requires no purification [9]. In that work, 1-dichloromethyl-β-carboline-3-carboxylate (7) was converted to the corresponding ester 8 in quantitative yield using ethereal diazomethane.…”