Synthesis of 2,3‐dihydro‐I H,4 H, 6 H‐furo[3,4‐b]pyrrolo[1,2‐a]quinoline‐6a(7H)‐carbonitrile; a novel type of intramolecular tetrahydrofuran formation

Appropriately 4-substituted 1,2,3,3a,4,5-hexahydro-3a-(methoxymethyl)pyrrolo[1,2-a]quinolines 3 cyclize to 2,3-dihydro-1H,4H,6H-furo[3,4-b]pyrrolo[1,2-a]quinoline-6a(7H)-carbonitrile (5) upon heating in polar solvents, the reaction being accelerated by lithium bromide. The formation of the annulated tetrahydrofuran ring of 5 takes place via intramolecular attack of the oxygen atom of the methoxymethyl substituent at C-3a on the electrophilic carbon atom at C-4. The structure of 5 was confirmed by single-crystal X-ray structure determination.