Total synthesis and absolute stereostructure of (+)-dysideapalaunic acid

Abstract

The total synthesis of (+)-dysideapalaunic acid, a sesterterpenic aldose reductase inhibitor, has been accomplished. Starting from optically active(8aS)-(+)-3,4,8,8a-tetrahydro-5,8a-dimethylnaphthalene-1,6(2H,7H)-dione, (5S)-(–)-3,4,4a,5,6,7,8,8a-octahydro-5,8a-dimethyl-5-(4methylpent-3-enyl)naphthalen-1(2H)-one ethylene acetal has been synthesized in eight steps involving reductive allylation, deoxygenation, and a Wittig condensation. Transformation of this ethylene acetal via methylation at C-2, Grignard addition, and a Horner–Emmons reaction furnished the required (+)-acid in eight steps. Thus, the absolute stereochemistry of the (+)-acid has been established as (4aS,5S,8aS).