Phenanthro[4,5-bcd]furan derivatives. VI. Some electrophilic substitution reactions and hydrogenation of 4H-cyclopenta[def]phenanthrene, phenanthro[4,5-bcd]furan, and 4H-benzo[def]carbazole.

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Some electrophilic substitution reactions and hydrogenation of 4H-cyclopenta[def]phenanthrene (1a), phenanthro[4,5-bcd]furan (1b), and 4H-benzo[def]carbazole (1c) have been investigated. The bromination of 1a and 1b with bromine gave the corresponding 8-bromo derivatives. The bromination of 1c however gave the 1,3,5,7-tetrabromo derivative as the sole product. The benzoylation of 1a and 1b afforded the corresponding 1-benzoyl derivatives, but in the case of 1c, the 1,7-dibenzoyl derivative was obtained together with the 4-benzoyl derivative. It appears that ortho- and para-orientation of the nitrogen atom in 1c is much stronger than that of the methylene group or the oxygen atom in 1a or 1b. Hydrogenation of 1a, 1b, and 1c with palladium–charcoal catalyst afforded the corresponding 8,9-dihydro derivatives (4a, 4b, and 4c). The reduction of 1a and 1c with sodium–ethanol gave 4a and 4c. The reduction of 1b however gave the 3,3a,8,9,9a,9b-hexahydro derivative. It appears that facile hydrogenation of the carbon-carbon double bonds at the 8,9-positions in 1a, 1b, and 1c are due to strain in the fused ring system.