Synthesis of (±)-Cathenamine and (±)-19-Epicathenamine, Isolated as Their C-21a-Cyano Derivatives

Recent progress in the chemistry of monoterpenoid indole alkaloids derived from secologanin

“…16 The same group have previously prepared O-Boc-Z-geissoschizine 36 which they have now converted into the key biosynthetic heteroyohimbine intermediates cathenamine 41 and 19-epicathenamine 40 via N-oxide 37. 17 The labile enamines were trapped as their cyanide adducts, as first described by Brown and Leonard some time ago. 18 Brown's rationalisation 19 that H-19a alkaloids must be formed from Zalkene intermediate 38 and H-19b alkaloids from E-alkene 39 was reiterated and it was stated that alkene isomerisation must therefore occur before formation of the major cyanide adduct 21-cyanotetrahydroalstonine 43 (15%) with H-19b stereochemistry.…”