Exploration of the Paterno-Buchi reaction as a potential route to the oxetan ring of taxol (R)

Two photochemical pathways to paclitaxel-like oxetan rings have been examin ed. In the first approach, an intramolecular Paterno-Buchi reaction on a 6, 7-enal was attempted without success. The intermolecular variation using a bicyclic alkene in the presence of either benzaldehyde or acetophenone deli vered oxetans whose regiochemistry was the same as that found in paclitaxel but opposite in stereochemistry. The crystal structures of a key intermedi ate diol and a photochemically generated oxetan are reported.