Synthesis of (±)-Pyrenolide B

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-oxocyclohexane-1-carboxylate ( 1 ) via ring enlargement of the bicyclic enol ether 5 (Scheme). Its reduction (NaBH₄ in EtOH) and subsequent protection with (t-Bu)Me₂Si resulted in the highly functionalized ten-membered lactone 9 . Introduction of the (Z)-configurated double bond, followed by deprotection and elimination of H₂O, gave (±)-pyrenolide B ( 12 ) in 16% overall yield.