Asymmetric protected 2-oxo-5-isopropyl-cyclohexenecarboxylates as key intermediates towards an EPC synthesis of (+)-heptelidic acid

Asymmetric shielded 2-oxo-5-isopropyl-cyclohexenecarboxylates 3n and 4n which are diastereomers at C-5′ have been prepared by a five step synthesis and separated by chromatography. Conjugate addition of (H₂C=CH)₂CuLi to 3n and 4n gave the adducts 13n (5′R,6′R) and 14n (5′S,6′R) as single diastereomers, respectively. Finally, the (5′R) configurated enoate 3n turned out to be valuable as chiral building block for an EPC synthesis of (+)-heptelidic acid.