An Intramolecular Diels–Alder Furan (IMDAF) Approach towards the Synthesis of Isoindolo[2,1-a]quinazolines and Isoindolo[1,2-b]quinazolines

An efficient approach to bridged pentacyclic nitrogen heterocycles via the tandem acylation/intramolecular Diels–Alder furan (IMDAF) reaction of 2-furylquinazolinones is described. Reactions of α,β-unsaturated acid anhydrides with 2-furyl-2,3-dihydroquinazolin-4-ones give 6b,9-epoxyisoindolo[2,1- a ]quinazolines in average yields. In this case, the exo -IMDAF reactions proceed with excellent diastereoselectivity giving five stereogenic centers and three new rings in one synthetic step. Isomeric 2,4a-epoxyisoindolo[1,2- b ]quinazolines are obtained by one-pot, three-component condensation reactions of allylamine, isatoic anhydride and furaldehydes involving the same IMDAF­ reaction as the key step. Some useful transformations including halogenation, hydrogenation, Prilezhaev epoxidation, and esterification of the synthesized epoxyisoindoloquinazolines are also demonstrated.