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We report herein the first total syntheses of four natural antibiotics, vermisporin, PF1052/AB4015-A, AB4015-L, AB4015-B, and one hydrogenated natural product derivative, AB4015-A2, that all feature a tetramic acid bearing cis-decalin ring. The construction of the functionalized cis-decalin ring was achieved by a diastereoselective intramolecular Diels-Alder (IMDA) reaction, which proceeded via a rare endo-boat transition state. Through an intramolecular neighboring-group-oriented strategy, the sterically hindered epoxy group in vermisporin, PF1052/AB4015-A and AB4015-L was installed efficiently. A one-pot aminolysis/Dieckmann condensation cascade using l-amino acid derivatives afforded the desired tetramic acid structure. The total synthesis led to the unambiguous verification of the absolute configuration of these natural products.
Dong et al. (Fri,) studied this question.