Tricyclic [10]annulenes. Part 7. Preparation, properties, and reactions of 7b-benzyl-7bH-cyclopent[cd]indene

Abstract

The tricyclic [10]annulene containing a central benzyl group, 7b-benzyl-7bH-cyclopent[cd]indene [1d], has been prepared from 7-methoxyindan-1-one by a sequence involving reductive alkylation to give the dienone (6), introduction of an extra double bond, and reaction of the resulting trienone (8) with methoxyvinyl-lithium to give the alcohol (9). Methylation and acid hydrolysis gave the diketone (4) which underwent intramolecular aldol condensation in the key step to give the tricyclic ketone (5). Conversion of (5) into the annulene (1d) was accomplished by reduction of the ketone, dehydration of the resulting alcohol, and final elimination of methanol. The annulene (1d) rearranges to the 2aH-isomer (13) on heating, and is readily nitrated, acetylated, and formylated in the 10π system. The reactivity of compound (1d) is compared and contrasted with that of the methyl annulene (1a).