Synthetic Study of Natural Metabolites Containing a Benzo[ c ]oxepine Skeleton: Heterocornol C and D.

A versatile strategy for the enantioselective synthesis of a benzo[ c ]oxepine structural core containing natural secondary metabolites was developed. The key steps of the synthetic approach include ring-closing alkene metathesis for seven-member ring construction, the Suzuki-Miyaura cross-coupling reaction for the installation of the double bond and Katsuki-Sharpless asymmetric epoxidation for the introduction of chiral centers. The first total synthesis and absolute configuration assignment of heterocornol D ( 3a ) were achieved. Four stereoisomers, 3a , ent - 3a , 3b and ent - 3b , of this natural polyketide were prepared, starting with 2,6-dihydroxy benzoic acid and divinyl carbinol. The absolute and relative configuration of heterocornol D was assigned via single-crystal X-ray analysis. The extension of the described synthetic approach is further presented with the synthesis of heterocornol C by applying the ether group reduction method to the lactone.