Role of conformational effects on the regioselectivity of macrocyclic INOC reactions: Two new asymmetric total syntheses of (+)-brefeldin A

We have gained some insight into the role of conformational effects on the regioselectivity of the macrocyclic intramolecular nitrile oxide cycloaddition observed in our (+)-brefeldin A synthesis. During the course of this regiochemical study, we have developed two novel stereoselective and regioselective schemes for total synthesis of (+)-brefeldin A (i.e. intramolecular nitrile oxide cycloaddition - isomerization and intermolecular nitrile oxide cycloaddition - ring closing metathesis strategies).