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Schiff bases derived from tryptamine react with Brassard's diene in the presence of EtAlCl2 to give functionalised 1,2,5,6-tetrahydropyridines which are subsequently transformed to indolo[2,3-a]quinolizines by Bischler-Napieralski reaction and reduction of the intermediate iminium salts with NaBH4.
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Lock et al. (1993) studied this question.
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