Partial synthesis of 6β-eudesmanolides and 6β-guaianolides from 6α-eudesmanolides: Synthesis of analogues of artepaulin, colartin and tannunolide D

Abstract

Epimerization at C-6 of polyfunctionalized 6α-eudesmanolides was achieved by chemical means, to obtain 6β-eudesmanolides and, after rearrangement, 6β-guaianolides. The epimerization process consists of the LiA1H 4 reduction of a 6α-lactone, selective protection of the hydroxymethylene group at C-12, oxidation and reduction at C-6 to epimerize this carbon, deprotection at C-12 and finally, lactonization with tetrapropylammonium perruthenate (TPAP) and 4-methylmorpholine N-oxide (NMO) in yields over 80%. The rearrangement of 1β-hydroxy-6β-colartin allow us to obtain 2,3-dihydro-6β-tannunolide D.