Enamines. III. A theoretical and photoelectron spectroscopic study of the molecular and electronic structures of aziridine enamines

Abstract

SummaryThe photoelectron (PE.) spectra of N-vinylaziridine (1) and some methyl and ethyl substituted derivatives are discussed in the light of quantum-chemical model calculations using the PRDDO SCF method. All aziridine enamines are found to exist as equilibrium mixtures of variable compositions, with an enamine-type conformation (I) generally as the major and a tram-bisected form (11) as the minor component . The PE. spectrum of the simplest aziridine enamine, N-vinylaziridine (l), shows a series of prominent IP. bands (Fig. I ) , the first two of which can be assigned to ionizations from (n, n)-dominant enamine orbitals. This assignment is supported by quantum-chemical predictions on the basis of Koopmans' theorem [ 141 using the PRDDO SCF method [15] as well as by a correlation of the ionization potentials of 1 with those of the constituents aziridine and ethylene (Fig. 2).Aziridine has four ionization potentials (IP.) below 14 eV [6] [16]. The first is well separated from the other three and can be safely assigned to n-type ionization. The next two IP. are due to ionizations from Walsh-type orbitals [ 171, denoted as ws (5 a') and wA (3 a") in Fig. 2. There is some controversy regarding the correct order of the corresponding ionic states. Whereas PRDDO and ab initio SCF methods at various 0018-0 19X

Rhodium-Catalyzed Stereoselective Formation of Z-Enamines from Allylaziridines

“…In contrast to previous reports, we did obtain the N -(1-propenyl)aziridine 2a , albeit with a low 25% conversion. Interestingly, unexpected selectivity for the Z -isomer 2a was observed (Table , entry 1) . There was no evidence for isomerization into the E -isomer in the course of isolation .…”