An oxetane ring can be constructed from 5α-acyloxy-Δ4(20)-taxoids. Hie facile intramolecular acyl migration from 5- to 20-position under slightly basic conditions enabled the construction of the oxetane ring in a convenient short cut, whereas the acyl migration from 2- to 20-position left the 2-hydroxyl accessible to a later benzoylation. An unexpected five-mem-bered 4-O, 20- O sulfite ring was formed in the attempted construction of the oxetane ring with 5α-triflate as a leaving group. After the construction of the oxetane ring, treatment with strong base LiHMDS and acetyl chloride gave the expected 4-O-acetate while treatment with acetic anhydride and DMAP gave a 4-O-acetoacetate. The oxetane ring can be constructed from 5α-acyloxy-Δ4 (20) -taxoids. Hie facile intramolecular acyl migration from 5- to 20-position under slightly basic conditions enabled the construction of the oxetane ring in a convenient short cut, whereas the acyl An unexpected five-mem-bered 4-O, 20-O sulfite ring was formed in the attempted construction of the oxetane ring with 5α-triflate as After leaving the construction of the oxetane ring, treatment with strong base LiHMDS and acetyl chloride gave the expected 4-O-acetate while treatment with acetic anhydride and DMAP gave a 4-O-acetoacetate.