Total synthesis and study of 6-deoxyerythronolide B by late-stage Cĝ€H oxidation

Among the frontier challenges in chemistry in the twenty-first century are the interconnected goals of increasing synthetic efficiency and diversity in the construction of complex molecules. Oxidation reactions of Cĝ€H bonds, particularly when applied at late stages of complex molecule syntheses, hold special promise for achieving both these goals. Here we report a late-stage Cĝ€H oxidation strategy in the total synthesis of 6-deoxyerythronolide B (6-dEB), the aglycone precursor to the erythromycin antibiotics. An advanced intermediate is cyclized to give the 14-membered macrocyclic core of 6-dEB using a late-stage (step 19 of 22) Cĝ€H oxidative macrolactonization reaction that proceeds with high regio-, chemo- and diastereoselectivity (40:1). A chelate-controlled model for macrolactonization predicted the stereochemical outcome of Cĝ€O bond formation and guided the discovery of conditions for synthesizing the first diastereomeric 13-epi-6-dEB precursor. Overall, this Cĝ€H oxidation strategy affords a highly efficient and stereochemically versatile synthesis of the erythromycin core.