Enantiospecific synthesis of (−)-3-iso-19,20-dehydro-β-yohimbine from secologanin: a route to normal and pseudo stereoisomers of yohimbine

Hydrolysis of secologanin ethylene acetal at pH 7 resulted in stereoselective aldol cyclisation to a cyclohexene aldehyde, which, on reductive amination and cyclisation with tryptamine afforded (−)-3-iso-19,20-dehydro-β-yohimbine, converted into various normal and pseudo isomers of yohimbine.