A macrocyclic β-iodoallenolate intermediate is key: synthesis of the ABD core of phomactin A.

An enantioselective strategy for the synthesis of phomactin natural products is described. The Lewis acid triggered cyclization of a β-iodoallenolate embedded in a 12-membered macrocycle was used to obtain a highly functionalized bicyclo[9.3.1]pentadecane in good yield and high diastereoselectivity. This iodoenone contains the substituents of the AD ring system of the phomactin family of natural products, appropriate for further functionalization. Synthesis of the oxadecalin core of phomactin A from the AD iodoenone intermediate was achieved. In this unusual strategy, rings A and B are both fashioned within a macrocyclic precursor.