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Furan's Gambit: Electrophile‐Attack‐Triggered Sacrifice of Furan Rings for the Intramolecular Construction of Azaheterocycles

“…Under the same conditions, 2‐(difurylmethyl)benzamides 36 afforded tetracyclic compounds 38 . The reaction proceeds via the intermediate formation of 4‐furylisoquinolones 37 followed by electrophilic attack of the ketone group on the second furan ring (Scheme ) 19,20. The tetracycles 38 were obtained in reasonable yields that did not depend significantly on the substituents on the benzene ring or the N atom, with the exception of the N ‐ tert ‐butyl derivative; in this case the reaction was accompanied by significant tarring, preventing isolation of any product.…”

Synthesis of the 4,10-Dihydro-3H-pyridazino[1,6-b]isoquinolin-10-one System by a Furan Recyclization Reaction

“…4 Over the past years we have developed a general synthesis of benzannelated heterocycles 2 using the recyclization of benzylfurans 1 with different nucleophilic substituents in the ortho position (Scheme 1). 5 This approach allowed us to synthesize substituted benzofurans, 6 indoles, 7 isocoumarins, 8 isoquinolones, 9 and isochromenes. 10 In all cases, recyclization proceeded without formation of 1,4-dicarbonyl compounds; a single masked carbonyl group participated in the new ring formation by interaction with the nucleophile located in the ortho position, the other one was liberated in the side chain as a ketone moiety.…”

Recyclization of Hydrazides of 2-Carboxyphenyldifurylmethanes: Synthesis of Novel 4,10-Dihydro-3H-pyridazino[1,6-b]isoquinolin-10-one System

“…8 In our conditions, if the benzylfuran 3 bears a second furan ring, recyclization is accompanied with a secondary intramolecular carbocyclization leading to tetracyclic derivatives 5 (Scheme 2). 5b, 6,7,9 To broaden the scope of our method for the synthesis of fused-ring heterocyclic compounds we tried to take advantage of the free keto group in further heterocyclizations. We reasoned that the introduction of the second nucleophilic center into a molecule of the starting compound 6 would allow us to redirect the secondary cyclization towards tricyclic compounds 7 according to Scheme 3.…”