AbstractAcetone extraction of cultures of the marine ascomyceteLeptosphaeria oraemaris(LINDER) on cornmeal disk gave the novel polyketide derivative leptosphaerolide ( = (+)‐7‐[(1E)‐l,3‐dimethylpent‐1‐enyl]‐10‐hydroxy‐3‐methoxybenzo[1,2‐b:5,4‐c′]dipyran‐2(9H)‐one; (4+)‐8) besides theo‐dihydroquinone 3‐[(1E)‐1,3‐dimethylpent‐1‐euyl]‐8,10‐dihydroxy‐7‐methoxy‐8‐(2‐oxopropyl)‐1H‐naphtho[2,3‐c]pyran‐9(8H)‐one (1) as a 10:9 mixture of epimers.retro‐Aldol reaction of1gave leptosphaerodione ( = (−)‐3‐[(1E)‐1,3‐dimethylpent‐1‐enyl]‐10‐hydroxy‐7‐methoxy‐1H‐naphtho[2,3‐c]pyran‐8,9(8H)‐dione; (−)‐6) which was also present in small amounts in the extracts and which gave1on reaction with acetone. It is thus likely that 1 is an artefact of the ex