Total synthesis of (±)-isoclovene

(±)-Isoclovene (I) was prepd. via an intramol. Michael addn. of the hydrindenone II, which was prepd. in 15 steps from the indandione III via stereoselective rearrangement of the spiro[dioxolane-indan] IV [RR1 = EtOC(:CH2) OCH2CH:) to IV (R = EtO2CCH2, R1 = vinyl)