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Wittig Cyclization of ω‑Hydroxy Hemiacetals: Synthesis of (+)-Aspicilin

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posted on 2017-07-27, 00:00 authored by René Schmidt, Michael Ostermeier, Rainer Schobert
The polyhydroxylated 18-membered lichen macrolide (+)-aspicilin was synthesized in 12 steps and 17% yield (longest linear sequence) starting from d-mannose and (S)-propylene oxide as the source of the stereogenic centers. Key steps were a palladium-catalyzed Csp3X–Csp3ZnX Negishi cross-coupling affording an ω-hydroxy hemiacetal which was macrocyclized via a domino addition–Wittig olefination reaction with the cumulated ylide Ph3PCCO. This synthetic approach also allowed a regioselective glycosylation of 6-OH of aspicilin with d-desosamine, a quick entry to chimeric macrolides with potential antibiotic activity.

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