SYNTHESIS OF 5-MEMBERED, 6-MEMBERED, AND 7-MEMBERED HETEROCYCLES BY INTRAMOLECULAR RING-OPENING REACTIONS OF 3-OXETANOL DERIVATIVES

Intramolecular ring opening reactions of 2-phenyl-3-oxetanols have bee n studied. The starting materials were prepared by the photocycloaddit ion of benzaldehyde and various silyl enol ethers. The intramolecular nucleophile was either incorporated into the silyl enol ether prior to the Paterno-Buchi reaction (oxetanes 3, 16) or was later installed by functional group interconversion (oxetanes 5. 12). With anionic heter oatom nucleophiles (O, N, S) which were attached to the carbon atom C- 3 of the trimethylsilyl-protected oxetanol via an alkyl chain, a subst itution at the less substituted position C-4 was observed and the corr esponding heterocycles (6, 8, 13, 19) were obtained in moderate to goo d yields (52-91%). Upon acid catalysis a ring opening of the Boc-prote cted 3-oxetanol 23 to cyclic carbonates occurred. The reaction did not proceed stereospecifically and resulted in a mixture of diastereomeri c products 24 and 25.