Rearrangements in Radical Cations of Diazoketones: A DFT Mechanistic Study

Publication date: Available online 5 May 2018 Source:Computational and Theoretical Chemistry Author(s): Ritu Arora, Kriti Kashyap, Rita Kakkar The mechanism of the Wolff rearrangement of some radical cations of diazocarbonyl compounds has been studied using density functional calculations. The C−C bond of diazoketones weakens slightly on cation formation, which lowers the barrier to the syn-anti isomerization of the radical cations, as compared to that of the neutral analogue. The effect of substitution on both carbonyl carbon and diazocarbon of the diazoethanal radical cation has been explored. The planarity of the syn and anti conformers is lost on reduction of diazoketones, and in most of the cases of substitution at the carbonyl carbon, the diazo moiety is out of the plane of the C=O group. The 1,2-rearrangement of radical cations preferably takes place in a stepwise manner, which involves the oxirene radical cation as an intermediate. The oxirene radical cation rearranges to the final product, the ketene radical cation, without any energy barrier. However, the carbene radical cation is involved in the Wolff rearrangement of the diazoethanal radical cation substituted at the diazocarbon atom by Ph, OMe or NH2. Graphical abstract

Source: Computational and Theoretical Chemistry - May 6, 2018 Category: Chemistry Source Type: research