Unveiling the [3+2] cycloaddition between difluoromethyl diazomethane and 3-ylideneoxindole from the perspective of molecular electron density theory†
Abstract
The [3+2] cycloaddition (32CA) reaction between difluoromethyl diazomethane (DFDAM) and 3-ylideneoxindole (3YOI) has been studied using molecular electron density theory at the M06-2X/6-311+G(d,p) computational level. ELF topological analysis of DFDAM characterizes this three-atom-component (TAC) as a pseudoradical species participating in the pseudomonoradical (pmr)-type 32CA reactions. Analysis of the conceptual DFT reactivity indices indicates that along a polar reaction 3YOI will act as the electrophile while DFDAM will act as the nucleophile. This 32CA reaction presents low activation enthalpy in dichloromethane, 8.2 kcal molā1. The reaction is endo selective and completely ortho regioselective in agreement with the experimental outcome. The strong exergonic character of this 32CA reaction, ā18.9 kcal molā1, makes it irreversible. The high global electron density transfer found at the most favorable ortho/endo TS, 0.24e, accounts for the highly polar character of this 32CA reaction, classified as the forward electron density flux. BET analysis along the most favourable ortho/endo reaction path asserts the pmr-type reactivity of this TAC. This 32CA reaction takes place through a non-concerted two-stage one-step mechanism characterized by the initial CāC single bond formation involving the pseudoradical C3 carbon of DFDAM.