Reinvestigation of the Biomimetic Cyclization of 3,5-Diketo Esters: Application to the Total Synthesis of Cyercene A, an α-Methoxy-γ-Pyrone-Containing Polypropionate

Abstract

The biomimetic cyclization of 3,5-diketo esters was reinvestigated for the synthesis of α-methoxy-γ-pyrones. 3,5-Diketo esters were selectively synthesized via the aldol reaction of commercially available methyl 2-methyl-3-oxopentanoate with an aldehyde followed by the oxidation with AZADOL® and PhI(OAc)2. The DBU-promoted intramolecular transesterification of 3,5-diketo esters showed excellent reactivity in MeOH, to give the corresponding γ-hydroxy-α-pyrones in high yields under mild reaction conditions. Based on the present cyclization scheme, the total synthesis of cyercene A was achieved.