Total synthesis of phenanthroindolizidine alkaloids via asymmetric deprotonation of N-Boc-pyrrolidine

A concise and efficient enantioselective strategy to synthesize two typical phenanthroindolizidine alkaloids, 14-hydroxyantofine and antofine, was developed, featuring an asymmetric deprotonation/diastereoselective carbonyl addition sequence during which the formation of a chiral C-13a center and connection of pyrrolidine and phenanthrene moieties were achieved efficiently in one step. The absolute configuration of the C-13a stereocenter can be delicately controlled by using different enantiomers of sparteine, both of which are commercially available.