The influence of protecting the hydroxyl group of β-oxy-α-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

Abstract

The in¯uence of protecting the hydroxyl group of a b-oxy-a-diazo carbonyl compound on the competition between the Wol rearrangement (WR) and the [1,2]-hydrogen shift (HS) was investigated theoretically. Stationary points on the potential-energy surface were located with the B3LYP density functional and the 6-31G** basis set. For the basic system geometry optimisations at B3LYP/6-311+G** were performed to validate the reliability of the B3LYP/6-31G** calculations. Singlepoint 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 theory of``atoms in molecules'' of Bader. The calculated energy barriers qualitatively predicted the yields of HS and WR obtained experimentally. In order to rationalise the calculated energy barriers, it was necessary to take into account not only the electronegativity of the protective groups but also the alignment of the migrating groups with the depletion sites at the carbene 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.

Developments in the Photochemistry of Diazo Compounds

“…[85] In some cases where Wolff rearrangement can compete with 1,2-H shift, namely in the case of an -oxy--ketocarbene, the use of water as solvent can even suppress the Wolff rearrangement product formation to exclusively yield 1,2-H migration product. [86,87] Recently, it was shown that the contribution from a free carbene to the alkene formation, which changes with the nature of the substituents, ranges from 60 % (R= Me) to 100 % (R=H) for the cases studied, however a dependence on the irradiation wavelength was observed. [88] In regarding to the migratory aptitudes of the substituents, the same trend described for the Wolff rearrangement was observed, since the migratory ability of a substituent is an inherent characteristic.…”