1,3-Cycloadditions of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide to furan, benzofuran, thiophen, and benzothiophen

The title nitrile oxide adds to furan and thiophen to give a single regioisomer, while the analogous cycloadditions to benzofuran and benzothiophen lead to both possible adducts. Side reactions occur in the case of thiophen. The orientation of the 1,3-cycloadditions was studied by a perturbational approach, using the CNDO/2 methods for computing molecular orbitals. Results are discussed in terms of the full intermolecular orbital theory as well as the frontier orbital method.