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■ Synthesis of 5-Substituted Indole Derivatives. Part 4: Naratriptan from α-Anilinoacetaldehyde Dimethylacetal by TiCl₄-Mediated Cyclisation

Béla Pete,* Gyula Simig, László Poszávácz, and László Toke

*Research Group of the Hungarian Academy of Sciences, Department of Organic Chemical Technology, Technical University of Budapest, H-1521 Budapest, Hungary

Abstract

N-Methyl-3-(1-methyl-4-piperidinyl)-1H-indole-5-ethanesulfonamide (Naratriptan, 2) was prepared from N-methyl-N-phenylmethyl-2-(4-aminophenyl)-ethanesulfonamide (3b) through reductive alkylation with dimethoxyacetaldehyde followed by N-acylation and TiCl₄-mediated indolisation, according to Sundberg procedure. The isopropyl group proved to be a useful protecting group for sulfonate esters in a number of transformations but was cleaved in the presence of TiCl₄.