Synthesis of Vinca Alkaloids and Related Compounds, XXXIV Synthesis of (3S, 14S, 16S)-Bromovincamines and Bromoapovincamines by Regioselective Bromination
By bromination of the iminium salt 2a (X‐Cl), the 9‐bromo derivative 2c (X=ClO4) is obtained in isomerfree state. Bromination of the lactam 8d leads to a ca. 7.5:1 mixture of 11‐bromo (8c) and 9‐bromo (8a) lactams. These precursors have been used to synthesize 9‐, 10‐ and 11‐bromovincamines (11a‐c), and 9‐, 10‐ and 11‐bromoapovincamines (12a‐c).