Short Total Syntheses of Both the Putative and Actual Structures of the Clerodane Diterpenoid (±)-Sacacarin by Double Annulation

[reaction: see text] The putative structure of the naturally occurring clerodane diterpenoid (+/-)-sacacarin has been prepared in only 10 steps, six of which are C-C bond-forming steps, in a chemo-, regio-, and diastereoselective manner. The key part of the synthesis is the double annulation (double Michael, Pinner, and Dieckmann reaction) of a tethered carbon diacid and 3-butyn-2-one. A corrected structure for sacacarin is proposed, and the structure is proven by synthesis.