Short total syntheses of both the putative and actual structures of the clerodane diterpenoid (+/-)-sacacarin by double annulation

[GRAPHICS] 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, an d Dieckmann reaction) of a tethered carbon diacid and 3-butyn-2-one. A corr ected structure for sacacarin is proposed, and the structure is proven by s ynthesis.