The Allylic Rearrangements (Claisen and Thio-Claisen) and Decomposition Reactions of Allyl Formate and its Sulfur Analogue: Density Function Theory Study and Nucleus-Independent Chemical Shifts

Theoretical studies of the Claisen and thio-Claisen allylic (3,3-sigmatropic) rearrangements and decomposition reactions of allyl formate (1) and allyl dithioformate (2), have been performed using density functional theory (DFT) and B3LYP and MPW1PW91 methods with a 6-31++G^** basis set. Of these DFT, the values for activation parameters obtained with the B3LYP/6-31++G^** method are in good agreement with the available experimental data. Transition states optimised at the B3LYP/6-31++G^** level of theory were used for calculating the nucleus-independent chemical shift (NICS). Our results indicate that the magnitudes of the aromatic characters of the transition states are not in agreement with the activation energies and therefore these reactions are not controlled by aromaticity, but are controlled kinetically by the aromaticity of the transition states.