Diazodiphenylethanone (1) reacts with acyclic enamino ketones 2 and enamino esters 3 to form products of electrophilic attack of diphenylketene at Cα (5) and nitrogen (6 and 7). The relative reactivity of the different enaminones was shown to be consistent with HOMO energies determined by the HAM/3 semiempirical method. However, this approach could not completely explain the reactivity of the cyclic enamino ketones 4, which, by HAM/3, show a high-energy second HOMO corresponding to the nonbonded pair of electrons on oxygen. © 1990 American Chemical Society.551751505155