Total Synthesis of (+/-)-Dendrobine

Article abstract of DOI:10.1021/ja00524a027

A total synthesis of (+/-)-dendrobine is described. (E,E,E)-Triene 9a, available stereoselectively in six steps from methyl 4-(diethylphosphono)crotonate, cyclizes by an intramolecular Diels-Alder reaction to afford 75-83percent of a mixture of four perhydroindanols containing 83percent of endo isomers 8a and 8b.Epimers 8a and 8b were transformed into nitrile 25 by two separate routes, each of which involves epimerization of C4, oxidation, angular methylation, and reductive cyanation.Nitrile 25 served as a precursor of amino ester 3 by two separate routes, the most efficient of which proceeded via bromolactone 40.Epoxidation of the trichloroethylurethane 58 prepared from 3 afforded a mixture of two epoxides, both of which were utilized in the synthesis.The minor epoxide, 59 (38-40percent yields), was transformed into dendrobine via methyl ketodendrobinate 57, while the major epoxide 60 (45-48percent yields) was recycled to 58.Additional strategies for the synthesis of dendrobine from 3 are discussed.