Photo-induced aromatic assembly of benzocycloalka[1,2-b] furan and spiro[furan-2(3H),1′-benzocycloalkane] derivatives

The photo-induced benzannulation of benzocycloalka[1,2-b]furans produced hydrohelicene-type compounds in good yields. A similar photoreaction of the spiro[furan-2(3H),1′-benzocycloalkane]s afforded dihydrophenalene derivatives in moderate yields. Benzo[kl]xanthene was also formed by a similar photoreaction of spiro[furan-2(3H),9′-xanthene]. The reaction pathway was elucidated by the 1H NMR spectrum of the reaction mixture and the alternative synthesis of the intermediate.