Paternò–Büchi reaction between furan and heterocyclic aldehydes: oxetane formation vs.metathesis.

The photochemical reaction of 2-substituted heterocyclic aldehydes with furan gave the corresponding exooxetane derivatives through the excited triplet state. However, in situthe oxetane derivatives were converted through a metathesis reaction into the corresponding Z,E-butadienyl formate derivatives. On the contrary, 3-substituted heterocyclic aldehydes gave the corresponding exooxetane derivatives. The effect of 2-substituted heterocyclic ring in order to facilitate the metathesis reaction is explained considering the possible participation of the π aromatic orbitals in the oxetane C–O bond cleavage. [ABSTRACT FROM AUTHOR]