Template-directed C-H insertion: Synthesis of the dioxabicyclo[3.2.1]octane core of the zaragozic acids

[GRAPHICS] The preparation of (+/-)-24, a model for the core of the zaragozic acids, i s reported. The pivotal reaction in this endeavor is the dirhodium(ll)catal yzed intramolecular C-H bond insertion of 2-diazoacetyl-1,3-dioxane 4, a tr ansformation which generates four of the six stereocenters present in the c ore structure. A novel method for the diastereoselective synthesis of pyruv ic acid acetals was also developed and employed in the preparation of 4 fro m xylitol derivative 7.