Tricyclic [10]annulenes. Part 2. Synthesis of 7b-methyl-7bH-cyclopent[cd]indene

Abstract

Four routes have been developed to the tricyclic [10]annulene, 7b-methyl-7bH-cyclopent[cd]indene (1), starting from the diester (2a), the tricyclic nitrile (6), or the tricyclic ketone (9). The best overall procedure involves the ketones (9a) and (15). The 2-substituted annulene nitrile (7), aldehyde (8), acid (17), amide (18), and ester (19) have also been prepared. The spectral properties of these and of (1) are consistent with a 10π-electron aromatic structure. When heated (1) rearranges to the 2aH-isomer (23).