Structure Assignment of Lagunapyrone B by Fluorous Mixture Synthesis of Four Candidate Stereoisomers

Techniques of fluorous mixture synthesis have been used to make four candidate stereoisomers for the natural product lagunapyrone B. A quasiracemic mixture of vinyl iodides whose component configurations at C19−21 were encoded by fluorous silyl groups was fused to a central fragment by a Negishi coupling. A separate quasiracemic mixture of pyrone fragments whose component configurations at C6,7 were also encoded by fluorous silyl groups was synthesized and demixed. Stille coupling of the resulting pure quasienantiomers with the quasiracemic mixture provided two quasi-diastereomeric samples, which were demixed and detagged to provide all four lagunapyrone B stereoisomers. Lagunapyrone was assigned the 6R,7S,19S,20S,21R configuration by comparison of optical rotations.