PURPOSE: To produce decarboxy-7,9-dihydrodendrobine useful for synthesizing natural (-)-dendrobine efficiently and selectively by taking advantage of chirality.
CONSTITUTION: (S)-Carvone of formula I is sterically selectively reduced to give a secondary alcohol derivative of formula II. The compound is converted to a phthalimide derivative of formula III wherein X is phthaloyl by inversion under a Mitsunobu reaction condition. The phthaloyl group of the compound is removed, carbamoylation and alkylation are successively carried out to give an N,N-disubstituted carbamic acid ester of formula III wherein X is CH2C≡CH or CO2Me. The compound is treated with dicobalt octacarbonyl, the prepared complex of formula IV is treated with 4-methylmorpholin-N-oxide and Pauson- Khand ring formation is promoted to give a tricycloenone derivative of formula V. A tricyclocarbamic acid ester (one of formula VI where X=H) is obtained from the compound through a tricycloketone derivative of formula VI and a dithian derivative and reduced to give the objective compound of formula VII.
INOMATA KOHEI
OGASAWARA KUNIRO
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