Boron trifluoride-catalyzed reaction of β-4(20)-epoxy-5-O-triethylsilyltaxinine A (1) gave the 3,5-diene (3) and the 3,8-cyclopropane (4) derivatives, while the similar reaction of the corresponding α-4(20)-epoxide (2) afforded the ring contracted derivative (5) and its hemiacetal dimer (6). Plausible mechanisms of these reactions containing 1,2-hydride shift (3 and 4 from 1) or pinacol-type rearrangement