Synthesis 2019; 51(09): 1949-1960
DOI: 10.1055/s-0037-1610684
paper
© Georg Thieme Verlag Stuttgart · New York

Unexpected PF6 Anion Metathesis during the Bischler–Napieralski Reaction: Synthesis of 3,4-Dihydroisoquinoline Hexafluorophosphates and Their Tetrahydroisoquinoline Related Alkaloids

a   Laboratorio de Química Orgánica y Biomolecular, CMN, Universidad Industrial de Santander, Parque Tecnológico Guatiguará, Km 2 Vía Refugio, Piedecuesta 681011, Colombia   Email: kouznet@uis.edu.co   Email: vkuznechnik@gmail.com
,
Mario A. Macías
b   Department of Chemistry, Universidad de los Andes, Carrera 1 No. 18A 10, Bogotá 111711, Colombia
,
a   Laboratorio de Química Orgánica y Biomolecular, CMN, Universidad Industrial de Santander, Parque Tecnológico Guatiguará, Km 2 Vía Refugio, Piedecuesta 681011, Colombia   Email: kouznet@uis.edu.co   Email: vkuznechnik@gmail.com
› Author Affiliations
We thank the Colombian Institute for Science and Research (COLCIENCIAS) under the project No. RC-0346-2013 for the financial support.
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Publication History

Received: 22 October 2018

Accepted after revision: 20 December 2018

Publication Date:
18 February 2019 (online)


Abstract

A series of N-phenethylcinnamamides were subjected to the Bischler–Napieralski reaction to furnish diverse 1-styryl-3,4-dihydroisoquinolines. We noticed that the desired products were unstable when the reaction was performed under conventional solvent conditions. However, when [bmim]PF6 was used as the reaction media, the nature of the Bischler–Napieralski reaction promoted an unusual in situ ionic interchange between this ionic liquid and the dihydroisoquinoline core that led to the stabilization of the desired 1-styryl-3,4-dihydroisoquinolines, allowing their isolation as hexafluorophosphate salts. Finally, the one-pot reduction/reductive methylation process afforded the N-methyl derivatives, establishing that our findings can be an efficient and useful strategy for the concise synthesis of tetrahydroisoquinoline alkaloids.

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