Synthesis of $\pm$-pyrenolide B

Abstract

In the synthesis of the title compound 12, the important intermediate 7 was obtained in good yield from the easily available ethyl 5,5-ethylenedioxy-2-oxocyclohexane1 --c arboxylate (1) via ring enlargement of the bicyclic enol ether 5 (Scheme). Its reduction (NaBH,, CeCI, in EtOH) and subsequent protection with (t-Bu)Me2Si resulted in the highly functionalized ten-membered lactone 9. Introduction of the (2)-configurated double bond, followed by deprotection and elimination of H20, gave (A)-pyrenolide B (12) in 16% overall yield.