Reactions of (Z/E)-2-phenyl-4-(α-arylethylidene)-5(4H)-oxazolones and Z-2-phenyl-4-arylmethylene-5(4H)-oxazolones with nucleophiles occur with retention of the exocyclic double band geometry, whereas reactions of E-2-phenyl-4-arylmethylene-5(4H)-oxazolones with some nucleophiles occur with total or partial isomerization. Structural calculations, MNPI and AM1, on model compounds reveal that the methyl group does not essentially affect the phenyl ring-double bond planarity. Application of the Klopman-Salem equation to the reaction of E-2-phenyl-4-benzylidene-5(4H)-oxazolone with different amines, calculated by MNDO, points to a reversible nucleophillc attack at the exocyclic carbon of this 5(4H)-oxazolone as a possible explanation of this behaviour. As Z-2-phenyl-4-benzylidene-5(4H)-oxazolone is more stable than the E-isomer, the opening reactions of the Z-compound occur without isomerization.

Peer reviewed