Biomimetic reactions of germacrenes

The biomimetic reactions of epoxygermacrene-D ($\text{1}$) with basic alumina afforded three new interesting compounds ($\text{4}$, $\text{5}$, and $\text{6}$), two of which ($\text{4}$ and $\text{6}$) have the same carbon skeleton as that of periplanone-A ($\text{3}$), a sexual stimulant for the American cockroach. The remaining one ($\text{5}$) is a bicyclo3.1.0]hexane derivative, from whch an axisonitrile-3 type compound ($\text{14}$) has been produced. Finally, preisocalamendiol ($\text{2}$) was also converted into $\text{6}$.