First synthesis and structural elucidation of (-)-presphaerene.

The first total synthesis of (-)-presphaerene (1) was achieved from (R)-glyceraldehyde 9 in 19 steps, demonstrating the novel "folding and allylic strain-controlled" intramolecular ester enolate S(N)2' alkylation strategy could be extended to the stereoselective synthesis of cyclopentanoid natural products. The present study also established the relative and absolute stereochemistry of 1, and the absolute structures of co-occurring sphaeroanes from the red alga Sphaerococcus coronopifolius.