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 (NaBH 4 in EtOH) and subsequent protection with ( t ‐Bu)Me 2 Si resulted in the highly functionalized ten‐membered lactone 9 . Introduction of the ( Z )‐configurated double bond, followed by deprotection and elimination of H 2 O, gave (±)‐pyrenolide B ( 12 ) in 16% overall yield.