mcdonabe

The first synthesis of hebelophyllene E is presented, along with assignment of its previously unknown relative configuration through synthesis of epi-ent-hebelophyllene E. Development of a catalytic enantioselective [2+2] cycloaddition of alkenes and allenoates provides access to the required chiral geminal dimethylcyclobutanes. Key to its success is the identification of a novel oxazaborolidine catalyst, which promotes the cycloaddition in high enantioselectivities with good functional group tolerance (9 examples, up to 97:3 er). Thus, a late-stage cycloaddition using a fully functionalized alkene followed by a diastereoselective reduction allows for a concise entry to this class of natural products.