15b, are described. The key intermediates, 1, 2, 3, 4-tetrahydro-8-methylfluorene-2- carboxylic acid (6a) and its 2-methyl analogue 6b, prepared by cycloaddition reactions, are converted into the corresponding a'-diazomethyl ketones lla and llb and are subjected to intramolecular ketocarbenoid addition and boron trifluoride-ethercatalyzed cyclization leading to cyclopropyl ketones 12a, b and A9J1-gibbenes 13a, b, respectively. Catalytic ...