A key step towards EPC synthesis of (+)-heptelidic acid

Absolute configuration of enoates 3n and 4n, which have been prepared as chiral building blocks for the EPC synthesis of the antibiotic (+)-heptelidic acid, was determined by X-ray structure analysis. Conjugate addition of an acetal protected vinylcuprate to the 5'R configurated enoate 3n gave adduct 9n as a single diastereomer in 79% yield. Further, cleavage of the auxiliary and of the acetal protecting group from 9n were studied. Finally, we obtained the silyl protected α-ketoester 13 in enantiomerically pure form, which is a known intermediate for the synthesis of heptelidic acid.