Clive Derrick L J, Stoffman Elia J L
Chemistry Department, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
Org Biomol Chem. 2008 May 21;6(10):1831-42. doi: 10.1039/b801858h. Epub 2008 Apr 1.
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.
