Transformations of the tetracyclic skeleton of eudistomins by neighboring‐group participation in the Mitsunobu reaction

Abstract

AbstractMitsunobu reaction mediated introduction of nitrogen nucleophiles into trans 1‐hydroxy eudistomins afforded in high yields rearranged products instead of the anticipated cis eudistomins due to neighboring group participations. Transannular interaction in the 6,5,6,7‐membered tetracyclic ring system of the sulfur atom in the 1,6,2‐oxathiazepine ring, to give a thiiranium ion containing intermediate, was followed by intermolecular attack of the present nucleophiles to give a 6,5,6,6‐membered tetracyclic ring system, now with a 1,5,2‐oxathiazine ring. Substitution of the hydroxyl group in a trans 1‐hydroxy dethia carba eudistomin derivative (i.e. with a 1,2‐oxazepine ring) also gave rearranged products due to transannular interaction from the bridgehead nitrogen atom, to give via an aziridinium ion intermediate, products with a 6,5,7,6‐membered tetracyclic ring system containing an 1,2‐oxazine ring.