IMDA-Radical Cyclization Approach to (+)-Himbacine

A formal total synthesis of the selective muscarinic receptor antagonist himbacine is presented. Key C−C bond-forming steps include an intramolecular Diels−Alder reaction, Stille coupling reactions, and a 6-exo-trig acyl radical cyclization to a conjugated enyne. An unexpected secondary alcohol to chloride conversion is witnessed during attempted thionocarbonate formation.