Synthesis 2019; 51(09): 2030-2038
DOI: 10.1055/s-0037-1611711
paper
© Georg Thieme Verlag Stuttgart · New York

Concise Synthesis of the ABC-Ring System of the Azafluoranthene, Tropoisoquinoline and Proaporphine Alkaloids: An Olefin Hydroacylation/Pomeranz–Fritsch Cyclization Approach

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Instituto de Química Rosario (IQUIR, CONICET-UNR) and Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina   Email: larghi@iquir-conicet.gov.ar   Email: kaufman@iquir-conicet.gov.ar
› Author Affiliations
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, PUE IQUIR-2016) and Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT, PICT 2014-0445 and PICT 2017-0149).
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Publication History

Received: 10 September 2018

Accepted after revision: 03 December 2018

Publication Date:
29 January 2019 (online)


Abstract

A straightforward approach toward a decorated cyclopenta[ij]isoquinoline embodying the ABC-ring system characteristic of the azafluoranthene (triclisine), tropoisoquinoline (pareitropone) and proaporphine (prodensiflorin B) alkaloids, is reported. The synthetic ­sequence entailed a novel 40% KF/Al2O3-mediated hydroacylation of a 2-allyl-benzaldehyde derivative, obtained in two steps from isovanillin, through O-allylation and Claisen rearrangement to assemble the AC-ring system. This was followed by an O-methylation and a reductive ­amination of the resulting indanone with aminoacetal. A modified Pomeranz–Fritsch cyclization was next implemented to install ring B, through sulfonamidation, followed by acid-promoted cyclization and ­final desulfonylation in situ.

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