Acid-Promoted Redox-Annulation toward 1,2-Disubstituted-5,6-dihydropyrrolo[2,1-α]isoquinolines: Synthesis of the Lamellarin Core

An efficient synthesis of a variety of 1,2-disubstituted-5,6-dihydropyrrolo[2,1-α]isoquinoline
derivatives via an acid-promoted cyclization reaction between 1,2,3,4-tetrahydroisoquinoline
(THIQ) and substituted α,β-unsaturated aldehyde derivatives
is reported. This cycloaddition allows access to structurally diverse
multisubstituted dihydropyrrolo[2,1-α]isoquinolines in moderate
to good yields, which was the core scaffold of marine natural alkaloid
lamellarins.