Total Syntheses of Rhodomolleins XX and XXII: A Reductive Epoxide-Opening/Beckwith-Dowd Approach.

A new TiIII -mediated reductive epoxide-opening/ Beckwith-Dowd rearrangement process efficiently assembles the bicyclo[3.2.1]octane framework of highly oxidized grayanane diterpenoids. By incorporation of a Cu(tbs)2 -catalyzed (tbs=N-tert-butylsalicylaldiminato) intramolecular cyclopropanation, a diastereoselective oxidative dearomatization-induced Diels-Alder cycloaddition and a MeReO3 -catalyzed Rubottom oxidation, this approach has enabled the first total syntheses of rhodomolleins XX and XXII in 23 and 22 steps, respectively.