A facile route to the pentacyclic lamellarin skeleton via Grob reaction between 3-nitro-2-(trifluoromethyl)-2H-chromenes and 1,3,3-trimethyl-3,4-dihydroisoquinolines

The basic structural framework of lamellarin alkaloids, 8,9-dihydro-6H-chromeno[4′,3′:4,5]pyrrolo[2,1-a]isoquinoline derivatives, has been obtained in good yields via Grob reaction between 3-nitro-2-(trifluoromethyl)-2H-chromenes and 1,3,3-trimethyl-3,4-dihydroisoquinolines in refluxing isobutanol. When the reaction was carried out in toluene at room temperature, only Michael adducts, as a mixture of two diastereomers, were isolated.