Regioselective formyloxylation of tetracyclic enone I with HCO2H gave 70% ketone II (R = HCOO), from which II (R = OH) was prepd. II (R = OH) serves as a starting material for cyclopentadiene derivs. III (RR1 = R3R4 = bond, R2 = H; RR4 = R1R2 = bond, R3 = H). The regioselective formyloxylation of I was confirmed by the crystal structure detn. of II (R = HCOO). Reaction of II (R = methanesulfonyl) with KOH-EtOH gave enone IV (X = O). Redn. of IV (X = O) with Dibal followed by dehydration with acidic Al2O3 gave III (RR1 = R3R4 = bond) (V), whereas reaction of tosylhydrazone IV (X = NNHSO2C7H7) with Na-triethylene glycol gave 48% III (RR4 = R1R2 = bond, R3 = H). V forms Diels-Alder products preferentially from its exo face. The crystal structures of the cycloaddn. products of V with maleic anhydride and N-phenyltriazolinedione were reported.