Synthesis of (-)-conocarpan by two routes based on radical cyclization and establishment of its absolute configuration.
Two independent routes for the total synthesis of the bioactive neolignan (-)-conocarpan are described. The first (98% ee) is based on formal radical cyclization onto a benzene ring, and involves a 5-exo-trigonal closure onto a double bond restrained within a 6-membered ring. The second route (88% ee), which is shorter, is based on 5-exo-trigonal cyclization of an aryl radical onto a pendant terminal double bond. The two routes differ in their degree of stereoselectivity. The absolute configuration originally assigned to (+)-conocarpan had previously been called into question on the basis of empirical chiroptical rules; the present chemical work confirms the need for revision, and the assigned absolute configurations of several compounds correlated with (+)-conocarpan must also be changed.
Clive
Derrick L J
DL
Chemistry Department, University of Alberta, Edmonton, Alberta T6G 2G2, Canada. derrick.clive@ualberta.ca
Stoffman
Elia J L
EJ
D001572:Benzofurans / Q000138:chemical synthesis* / Q000737:chemistry; D003500:Cyclization; D005609:Free Radicals / Q000737:chemistry; D015394:Molecular Structure
D001572:Benzofurans; D005609:Free Radicals; C447284:conocarpan