Neat total synthesis of six monoterpenic alkaloids of the actinidine series

Abstract

A concise enantiopure synthesis of six monoterpenic alkaloids of the actinidine series possessing a cyclopenta[ c]pyridine skeleton, (+)-deoxyrhexifoline ( 4), (+)-boschniakinic acid ( 5), (+)-boschniakine ( 6), (−)-plantagonine ( 7), (−)-indicaine ( 8) and (−)-tecostidine ( 9) is reported starting with the chiral precursor 3-bromo-5-((4 R)-phenyloxazolin-2-yl)pyridine ( 10). It involves a C-4 regioselective connection of a butene appendice and an intramolecular 5- exo- trig Heck annulation sequence followed by hydrogenation of the exocyclic alkene. Mixture of (3 R)- and (3 S)-7-((4 R)-phenyloxazolin-2-yl)cyclopenta[ c]pyridines was separated by HPLC before being transformed into enantiopure natural products ( 4– 9) by modification of the oxazoline group.