X=Y-ZH COMPOUNDS AS POTENTIAL 1,3-DIPOLES. PART 23. MECHANISM OF THE REACTIONS OF NINHYDRIN AND PHENALENE TRIONE WITH α-AMINO ACIDS. X-RAY CRYSTAL STRUCTURE OF PROTONATED RUHEMANN'S PURPLE, A STABLE AZOMETHINE YLIDE

Article abstract of DOI:10.1016/S0040-4020(01)89244-9

The ninhydrin reaction is shown to involve stereopecifically formed azomethine ylides of two types by trapping of the intermediates with maleimides as dipolarophiles.One type of azomethine ylide, in which the carboxyl group of the original α-amino acids i