The ozonolysis of ()-longifolene (1) in different solvents (Et 2 O, CH 2 Cl 2 , CHCl 3 , acetone) at À 808 provided quantitatively longifolene epoxide (3) as a single diastereoisomer in which the O-atom is endopositioned (Scheme 2). Upon warming to room temperature, the epoxide remained stable only in acetone and was isolated as a low-melting crystalline compound. In CH 2 Cl 2 , Et 2 O, or CHCl 3 solution, epoxide 3 rapidly rearranged to the isomeric enols 4 and 5, which underwent further rearrangement to give the exo-aldehyde 6. On standing for several weeks in CH 2 Cl 2 solution, or in CHCl 3 and Et 2 O as well, at room temperature, aldehyde 6 slowly rearranged into its epimer 7. The aldehydes 6 and 7 were isolated on the preparative scale for further synthetic use. The addition of methylmagnesium iodide to 6 and 7 provided the corresponding alcohols 13/14 and 15/16, respectively, which were isolated as pure diastereoisomers (Scheme 4). The configurations of the new chiral centers in 13 ± 16 were determined by NMR methods and X-ray crystallography.