Studies directed toward the total synthesis of azaspiracid. Construction of the C1–C19 carbon backbone and synthesis of the C10, C13 nonnatural transoidal bisspirocyclic ring system

The efficient entry to the C1–C19 carbon backbone of azaspiracid is outlined utilizing a key Julia coupling strategy. Spirocyclization of a C12 sulfone substrate induced formation of the unprecedented, nonnatural transoidal bisspiroketal. Construction of the bisspirocyclic array at C10 and C13, in the absence of the C12 sulfone, led to formation of the cisoidal orientation of the bisspirocycle, with the nonnatural stereochemistry at C13.