Intramolecular Hetero-Diels–Alder Reactions Catalyzed by BiCl3: Stereoselective Synthesis of Benzo-Annelated Decahydrofuro[3,2-h][1,6]naphthyridine Derivatives

A novel, efficient synthesis of a series of functionalized, benzo-annelated decahydrofuro[3,2-h][1,6]naphthyridine derivatives 3 has been achieved. The protocol is based on the intramolecular hetero-Diels–Alder (IMHDA) reaction of in situ formed imines derived from an N-prenylated sugar aldehyde 1 and different aromatic amines 2 in the presence of bismuth(III) chloride as catalyst. The reactions could be run under very mild conditions at room temperature, and were complete within 30 min, affording exclusively and stereoselectively the corresponding trans-fused products 3 in good-to-excellent yields (Table).