Synthesis of the tricyclic indole alkaloids, dilemmaones A and B

Tetrahedron. 2019 Dec 6;75(49):130714. doi: 10.1016/j.tet.2019.130714. Epub 2019 Oct 21.

Abstract

Dilemmaones A-C are naturally occurring tricyclic indole alkaloids possessing a unique hydroxymethylene or methoxymethylene substituent at the C2 position of the indole core and a C6-C7 fused cyclopentanone. Dilemmaone B has been prepared in 5 steps from 5-methylindan-1-one, and dilemmaone A has been prepared in 3 steps from a common precursor, 6-bromo-5-methyl-7-nitroindan-1-one. In both syntheses, key steps include a Kosugi-Migita-Stille cross coupling and a reductive cyclization using hydrogen gas and a transition metal catalyst.