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

VARGAS, DIDIER; LARGHI, ENRIQUE; KAUFMAN, TEODORO

SYNTHESIS-STUTTGART

GEORG THIEME VERLAG KG

Lugar: Stuttgard; Año: 2019 vol. 51 p. 2030 - 2038

0039-7881

A straightforward approach toward a decorated cyclopenta[ij]isoquinoline embodying the ABC-ring system characteristic of theazafluoranthene (triclisine), tropoisoquinoline (pareitropone) andproaporphine (prodensiflorin B) alkaloids, is reported. The synthetic sequenceentailed 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 ACringsystem. This was followed by an O-methylation and a reductive aminationof the resulting indanone with aminoacetal. A modified Pomeranz?Fritsch cyclization was next implemented to install ring B, throughsulfonamidation, followed by acid-promoted cyclization and final desulfonylationin situ.