Concise synthesis of the ABC-ring system of the azafluoranthene, tropoisoquinoline and proaporphine alkaloids. An olefin hydroacylation/ Pomeranz-Fritsch cyclization approach

TEODORO S. KAUFMAN; TEODORO S. KAUFMAN; ENRIQUE L. LARGHI; ENRIQUE L. LARGHI; DIDIER F. VARGAS; DIDIER F. VARGAS

SYNTHESIS-STUTTGART

GEORG THIEME VERLAG KG

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 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 in situ desulfonylation.