Synthesis of (-)-conocarpan by two routes based on radical cyclization and establishment of its absolute configuration |
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Authors: | Clive Derrick L J Stoffman Elia J L |
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Institution: | Chemistry Department, University of Alberta, Edmonton, Alberta T6G 2G2, Canada. derrick.clive@ualberta.ca |
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Abstract: | 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. |
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