Synthetic Efforts and Ultimate Limitation to an Asymmetric Achmatowicz Approach Toward EBC-23.

An effort toward the total synthesis of the polyketide natural product EBC-23 is reported. The asymmetric approach is convergent and uses a late-stage Claisen-like enolate/acid chloride coupling to establish a key 1,3-diketone intermediate. The 1,3-diketone target is an oxidized form of the hydrated natural product, which fails to spiroketalize. The convergent asymmetric synthesis uses an asymmetric Noyori transfer hydrogenation of a ß-furyl ketoester to enantioselectively form a chiral furyl alcohol. An Achmatowicz/Jones/Luche three-step reaction sequence was used to stereoselectively convert the furyl alcohol into the 5-hydroxy-pyran-2-one. The absolute stereochemistry of the 1,3-polyol fragment was established by a Leighton allylation. A subsequent Grubbs cross-metathesis, and Evans acetalation were used to install the 1,3-syn-diol stereochemistry.