Stereoselective Total Syntheses of Guanacastepenes N and O

Total syntheses of (+/-)-guanacasteenes N and 0 were accomplished with 2-cycloheptenone as starting material. The six- and five-membered rings of the,core [5, 7, 6] ring skeleton Were constructed with an intramolecular Diels-Alder reaction and alpha-carbonyl radical cyclization. The quaternary Centers and their stereochemistry were established with sequential Cu(I)-mediated conjugate additions. A sequence with dihydroxylation, conjugate addition, and beta-elimination was devised to incorporate all Oxygen functionalities at positions. The total synthesis is adaptable for the synthesis of enantiopure guanacastepenes N and O using chiral intermediate (R)-3-vinyl-2-cycloheptenol obtained from lipase-catalyzed kinetic resolution.