A Cycloaldol Approach to the Isobenzofuran Core of the Eunicellin Diterpenes

A novel cycloaldol approach to the isobenzofuran core common to many of the eunicellin diterpenes is described. The cycloaldol precursor was prepared by aldol addition of (S)-(+)-carvone and methacrolein followed by etherification to a glycolate ester. Chemoselective enolization of the glycolate ester led to the cycloaldol adduct in high yield and diastereoselectivity. An oxidative rearrangement−allylic diazene rearrangement sequence established the requisite cis ring fusion.