Constructing the architecturally distinctive ABD-tricycle of phomactin A through an intramolecular oxa-[3+3] annulation strategy

Our efforts in constructing the ABD-ring of phomactin A through an intramolecular oxa-[3+3] annulation strategy is described. This struggle entailed finding a practical and efficient preparation of annulation precursor, and a realization of the unexpected competing regioisomeric pathway. The success entailed accessing the A-ring through Diels-Alder cycloaddition of Rawal’s diene. Furthermore, the discovery that the regioisomers from the annulation existed as atropisomers with respect to the D-ring olefin and that they could be equilibrated to the desired ABD-tricycle, allowing large quantities of tricycle to be accessed.