Two sex pheromones of the American cockroach, periplanone A and B, have been isolated by Persoons et al. The structure of the latter was proposed by the same authors, and then its stereostructure including the absolute configuration was unambiguously determined by its synthesis. Furthermore, the structure (1) of periplanone A has been proposed by Persoons et al., on the basis of its spectral data together with some chemical evidence, but the stereochemistry was not known. In order to elucidate the structure of periplanone A, the authors have synthesized two possible hydroazulenones (5 and 6) from germacrene-D by using biomimetic transannular reactions as a key step. However, the spectral data of synthetic compounds were entirely different from those of natural one. Therefore, the ^1H NMR and IR spectral data of periplanone A and its rearrangement product were reexamined, consequently, the structures of both compounds were found to be resembled each other. Clearly, the structure of periplanone A, which is quite labile as compared with the rearrangement product, seems to be represented by one of the possible decalones (I or II), while the latter must be depicted by III or IV. As shown in Table 1 and 2, the coupling constants based on the conformations I and III, obtained from molecular mechanics calculations, were compatible with the observed ones for periplanone A and rearrangement product, respectively. Thus, the stereostructure of periplanone A was elucidated as I.
