STEREOSELECTIVE SYNTHESIS OF THE BIS-TETRAHYDROFURAN FRAGMENT (C-1-C-9) OF ASTELTOXIN

An 18-step synthesis of the chiral bis-tetrahydrofuran fragment 2 of a steltoxin 1 is described. This synthesis proceeds under practically co mplete substrate stereocontrol, starting with compound 5a. From there the chirality centers of 2 are generated with >95% ds each by using a sequence of Claisen rearrangement, chelate Cram Grignard addition, and osmylation reactions. The current synthesis affords 2 in racemic form . The key intermediate 8 was also synthesized with ee > 96%, which sho uld provide access to 2 in both enantiomeric forms.