According to Tanaka, Kashiwada, and co-workers hypatulin B (3) could be produced by oxidative cleavage and methylation through a biogenetic pathway from hypatulin A (2). The structural assignment of C-3 was supported by chemical conversion of hypatulin A (2) into hypatulin B (3) by a retro-Dieckmann-type cleavage using N,N-dimethylaminopyridine (DMAP) in MeOH.