Total Synthesis and Stereochemistry of Alternaric Acid

Determination of the stereochemistry and the total synthesis of alternaric acid 1 has been achieved. The stereostructure of 1 has been elucidated by stereoselective synthesis of four diastereoisomers of the C(9)-C(14) fragment 6, which had been obtained as a degradation product during structural studies. Key reactions of the total synthesis of 1 include the Julia olefination of tertiary aldehyde 6 and phenylsulfone 7 and novel one-pot construction of 3-acyl-4-hydroxy-5,6-dihydro-2-pyrone via Fries-type rearrangement of the O-enol acyl group of β-keto-δ-valerolactone toward the α-position of the δ-lactone. The absolute configuration of alternaric acid has been shown to be that illustrated in structure 1. The modified Fries-type rearrangement method has also been extented to the synthesis of some other compounds containing a tricarbonylmethane structure