X=Y-ZH COMPOUNDS AS POTENTIAL 1,3-DIPOLES. PART 28. THE IMINIUM ION ROUTE TO AZOMETHINE YLIDES. BACKGROUND AND REACTION OF AMINES WITH BIFUNCTIONAL KETONES.

Article abstract of DOI:10.1016/S0040-4020(01)96013-2

The reaction of isatin, ninhydrin and acenaphtenequinone with primary and secondary amines gives rise to stereospecific formation of intermediate azomethine ylides which can be trapped by cycloaddition to methyl acrylate or N-methylmaleimide.The regiochemistry of the cycloadditions to methyl acrylate is controlled by both frontier orbital and steric interactions with the latter dominating in the examples studied.