Lewis acid mediated condensation reactions of α,β-unsaturated acids with 4-hydroxy-2-pyrones. A concise structural assignment of Fleischmann’s α,α-bispyrone and Praill’s α,γ-bispyrone

Unambiguous assignments of Fleischmann’s α,α-bispyrone 3 and Praill’s α,γ-bispyrone 6 have been carried out by exploring Lewis acid mediated condensation reactions of α,β-unsaturated carboxylic acids with 4-hydroxy-2-pyrones. This protocol is shown to be useful for synthesis of a BCDE-ring tetracyclic analog of arisugacin.