Peculiarities of the cascade cleavage of the polarized C≡C-fragment in α-ketoacetylenes on reaction with ethylene diamine

The reaction of diarylketoacetylenes with ethylenediamine (EDA) leads to arylmethylketones and 2-substituted imidazoline derivatives. This transformation involves complete cleavage of the triple bond via initial intermolecular Michael-addition with subsequent intramolecular Michaeladdition. Final fragmentation can be presented as a retro-Mannich reaction, accompanied by three formal reductive stages (formation of three C-H bonds), while the other carbon undergoes a formal oxidation, in which three C-N bonds (C-N and C=N) are formed.