In connection with periplanone A, acid-catalyzed reaction of germacrene-D epoxide has been carried out using A1C13 in ether to afford a hydroazulene which has been further transformed into one of the hydroazulenones proposed to be periplanone A. TWO sex pheromones of the American cockroach Periplaneta americana, PeriPlanOne A and Peri, planone B, which enter into the corresponding different receptors,ls2 have been isolated by Persoons et a1.l The former has been also detected by Nishino et a1.2 Of these two compounds, the stereostructure of periplanone B has been unambiguously determined as b3 Furthermore, the structure (.) of periplanone A has been proposed by Persoons et al., on the basis of its spectral data together with some chemical evidence. 4 In 1986, however, Hauptomann et al. have reported on the isolation and structure of an epoxygermacrone (a, a common precursor of both periplanone A and periplanone B, and named it as periplanone A,5 although its spectral data are completely different from those of Persoons' periplanone A. On the other hand, we reported the revised structure (4_) of Persoons' periplanone A on the basis of an exhaustive comparison of spectral data among the synthetic hydroazulenone (k),6 periplanone A and its rearrangement product.4y6 Quite recently, however, Macdonald et al. proposed that germacratrienone oxide (6_), a stereoisomer of 2, is periplanone A.' In addition, they assigned the structure of Persoons' periplanone A to be2,' which contains a rare trans-fused oxabicyclo[3.3.0]-