An ab initio and X-ray study of morpholinone derivatives: the intermolecular 1,3-dipolar cycloaddition of a derived ylide with maleimide

Conformational analysis of N-acetyl 5-phenyl-morpholin-2-one, shows two main conformers. That which is also observed in the crystal structure determination contains the C(5)-phenyl substituent in a pseudo-axial position. The favored conformations of the paraformaldehyde-derived ylide, 1, were similarly established and two conformers were also found distinguished by the position of the C(5)-phenyl group either in a pseudo-axial or equatorial position. Four reaction pathways for the cycloaddition of maleimide with each ylide conformer, have been examined by ab initio methods (HF/6-31+G∗ and B3LYP/6-31+G∗) and our calculated transition state energies are in good agreement with the ratio of products observed experimentally.