The influence of protecting the hydroxyl group of beta-oxy-alpha-diazo carbonyl compounds in the competition between Wolff rearrangement and [1,2]-hydrogen shift. Density functional theory study and topological analysis of the charge density

The influence of protecting the hydroxyl group of a beta-oxy-alpha-diazo ca rbonyl compound on the competition between the Wolff rearrangement (WR) and the [1,2]-hydrogen shift (HS) was investigated theoretically. Stationary p oints on the potential-energy surface were located with the 6-31G** density functional and the 6-31G** basis set. For the basic system geometry optimi sations at B3LYP/6-311+G** were performed to validate the reliability of th e B3LYP/6-31G** calculations. Single point energy calculations were carried out at the B3LYP/6-311+G** level on the B3LYP/6-31G"*-optimised geometries . Further insight into the processes was achieved with the aid of the theor y of "atoms in molecules" of Bader. The calculated energy barriers qualitat ively pre dieted the yields of HS and WR obtained experimentally. In order to rationalise the calculated energy barriers, it was necessary to take int o account not only the electronegativity of the protective groups but also the alignment of the migrating groups with the depletion sites at the carbe ne centre. Further, when the hydroxyl group was not protected the existence of an intramolecular hydrogen bond played an important role in both HS and WR.