Imidoylketene-α-oxoketenimine and α-oxoketene–α-oxoketene rearrangements. 1,3-Shifts of substituted phenyl groups

Abstract

1,3-Phenyl shifts interconvert imidoylketenes 1 and α-oxoketenimines 2 and, likewise, α-oxoketenes 3 automerize by this 1,3-shift. These rearrangements usually take place in the gas phase under conditions of flash vacuum thermolysis. Energy profiles calculated at the B3LYP/6-31G(d,p) and B3LYP/6311 + G(3df,2p)//B3LYP/6-31G(d,p) levels demonstrate that electron donating substituents (D) in the migrating phenyl group and electron withdrawing ones (W) in the non-migrating phenyl group, can stabilise the transition states TS1 and TS2 to the extent that activation barriers of ca. 100 kJ mol⁻¹ or less are obtained; i.e. enough to make these reactions potentially observable in solution at ordinary temperatures. The calculated transition state energies ΔG(TS1) show an excellent correlation with the Hammett constants σ_p(W) and σ_p⁺(D).