Méthylène-indolines, indolénines et indoléniniums—XIII: L'hydroxy-16 déhydro-1 vincadifformine, intérmédiaire dans le réarrangement biomimétique de la vincadifformine en vincamine

Abstract The title compound is a crucial intermediate in the biomimetic conversion of vincadifformine 1 into vincamine 7 . Its configuration at C-16 is established by a combination of chemical and spectroscopic evidence. Iodine oxidation converts 14 into the bridged lactam 18 , thus proving a β configuration for the hydroxy group at C-16. The same reaction applied to vindoline 19 gives 21 identical with one of the compounds obtained by microbiological transformation of 19 . The 13 C NMR spectra of derivatives 3 and 8 (obtained by oxidation of vincadifformine) show that oxidation proceeds with introduction of the substituent at C-16, with a β-configuration. The alcohol 3 however, posesses a different conformation due to strong hydrogen bonding with N-4.