Synthesis of the core of apicularen A by transannular conjugate addition

The synthesis of the core of the myxobacteria metabolite apicularen A by a novel transannular 1,4-addition is described. The key step involved acid mediated transannular conjugate addition of the C13 hydroxyl into the α,β-unsaturated ketone in macrolactone 18 to provide the trans-pyranone 19 and the cis-isomer 20 in a ratio of 9:1, respectively.