Synthesis of (+)-Manoalide via a Copper(I)-Mediated 1,2-Metalate Rearrangement

An enantiospecific synthesis of the phospholipase A2 inhibitor (+)-(4R)-manoalide is reported in which all 25 carbons of the sesterterpenoid skeleton are constructed from 3-furaldehyde, trimethylalane, oxirane, CO, β-ionone, and propargyl bromide. The overall yield for the longest linear sequence (12 steps) is 12%. Key steps include (a) a zirconium-catalyzed carboalumination reaction to construct the C10−C11 trisubstituted alkene, (b) a Cu(I)-mediated 1,2-metalate rearrangement to construct the C6−C7 trisubstituted alkene, (c) a Sharpless kinetic resolution to secure the (4R)-stereochemistry, (d) generation of a 5-stannyl-2,3-dihydrofuran by Mo-catalyzed cycloisomerization of a homopropargylic alcohol, and (e) construction of the hydroxyfuranone ring by photooxidation of a silylfuran.