Flash vacuum thermolysis generation and a UV-photoelectron spectroscopy study of the N-substituted iminoacetonitriles

Flash vacuum thermolysis of cis and trans 1-benzyl and 1-allyl-2-cyano-3-phenylzetidines (1a and 1b) at 470 °C resulted in the formation of E and Z isomers of N-benzyl and N-allyl iminoacetonitriles 2a and 2b, respectively, beside small amounts of products 3a and 3b of their [1,3] prototropic shifts. It was found that the thermal fragmentation of the azetidine ring occurred fully regioselectively with a cleavage of the C2–C3 and C4–N bonds, but not the N–C2 and C3–C4 bonds. The UV-photoelectron spectrum of compound 2b was measured and analyzed with the aid of quantum chemical calculations of ionization energies. The strong modification of the electronic structure of the simplest carbon–nitrogen double bond upon the α,β substitution is due to the combined electron-withdrawing effect of the nitrile group and the donor effect of the allyl group.