Bioinspired Synthesis of (-)-PF-1018

摘要

The combination of electrocyclizations and cycloadditions accounts for the formation of a range of fascinating natural products. Cascades consisting of 8 pi electrocyclizations followed by a 6 pi electrocyclization and a cycloaddition are relatively common. We now report the synthesis of the tetramic acid PF-1018 through an 8 pi electrocyclization, the product of which is immediately intercepted by a Diels-Alder cycloaddition. The success of this pericyclic cascade was critically dependent on the substitution pattern of the starting polyene and could be rationalized through DFT calculations. The completion of the synthesis required the instalment of a trisubstituted double bond by radical deoxygenation. An unexpected side product formed through 4-exo-trig radical cyclization could be recycled through an unprecedented triflation/fragmentation.