The first example of an intramolecular Diels–Alder furan (IMDAF) reaction of iminium salts and its application in a short and simple synthesis of the isoindolo[1,2-a]isoquinoline core of the jamtine and hirsutine alkaloids

1-(2-Furyl)-3,4-dihydroisoquinolines, easily prepared from readily available phenethylamines, undergo tandem alkylation/[4+2]-cycloaddition with allyl halides. The reaction proceeds via 2-allyl-1-furyl-3,4-dihydroisoquinolinium salt formation and subsequent intramolecular exo-Diels–Alder reaction of furan with the allyl fragment (IMDAF reaction). The adducts formed include the basic structural element of the isoindolo[1,2-a]isoquinoline alkaloids jamtine and hirsutine.