7, 7-Dimethyltricyclo[3.3.0.0^{2, 8}]octan-3-ones as Synthetic Intermediates. VI. An Improved Formal Synthesis of (±)-Descarboxyquadrone via Highly Regioselective Cyclopropane Ring Opening of Tricyclo[3.3.0.0^{2, 8}]octan-3-one

Abstract

The cyclopropane ring opening reaction of 7, 7-dimethyl-3-oxotricyclo[3.3.0.0^{2, 8}]octane-5-acetic acid (5) was examined. A regioselective C(1)-C(2) bond cleavege of 5 proceeded smoothly under acidic conditions to give a bicyclo-[3.2.1]octan-3-one derivative 7 in good yield, as a result of neighboring-group participation of the carboxyl group. The lactone 7 was then successfully transformed into the 1, 4-diketone 9, a useful intermediate for total synthesis of (±)-descarboxyquadrone (4).