Facile Strategy to Access the Indolo[2,3-a]quinolizidine Framework: Synthetic Study on Tangutorine^[1]

^§ These authors have contributed equally to this manuscript.

Abstract

An asymmetric synthetic approach to indolo[2,3-a]quinolizidine framework has been developed involving Horner–Wadsworth–Emmons olefination and reductive amination as the key steps. Further, the developed strategy was explored towards the synthesis of tangutorine using Evans aldol reaction for the preparation of desired aldehyde.

Key words

indolo[2,3-a]quinolizidine - Horner–Wadsworth–Emmons reaction - piperidine - tangutorine

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Conditions attempted for intramolecular C3 acylation:
• 15a MeSO₃H, 70 °C, 4 h – inseparable mixture of polar compounds.
• 15b pTSA, toluene, reflux, 12 h – no product.
• 15c PPA, 70 °C, 12 h – no reaction progress.