Tricyclic [10]annulenes. Part 6. Preparation and properties of 7b-ethyl-and 7b-isopropyl-7bH-cyclopent[cd]indenes

Abstract

Previous syntheses of 7b-methyl-7bH-cyclopent[cd]indene (1a) have been extended to the 7b-ethyl (1b) and 7b-isopropyl (1c) analogues. All three compounds have similar u.v. and n.m.r. spectra, entirely consistent with their delocalised 10π aromatic structure. The 7b-ethyl compound undergoes thermal sigmatropic rearrangement to the 2aH-isomer eleven times faster than the 7b-methyl analogue.