A Common C-2-Symmetric 2,2'-Biphenol Building Block and its Application in the Synthesis of (+)-di-epi-Gonytolide A

A variety of biaryl polyketides exhibit remarkable bioactivities. However, their synthetic accessibility is often challenging. Herein, the enantioselective preparation and synthetic application of an axially chiral 2,2'-biphenol building block is outlined that represents a common motif of these intriguing natural products. Based on the highly regioselective and scalable bromination of a phenol precursor, a coupling process by Lipshutz cuprate oxidation was developed. A copper-mediated deracemization strategy proved to be superior to derivatization or kinetic resolution approaches. Key steps in the overall building block synthesis were rationalized through DFT studies. Utilizing the 2,2'-biphenol, a highly diastereoselective five step synthesis of formerly unknown (+)-di-epi-gonytolide A was developed, thus showcasing the building block's general potential for the synthesis of natural products and their derivatives. En route, the first enantioselective construction of a chromone dimer intermediate was established.