Unveiling the high reactivity of strained dibenzocyclooctyne in [3 + 2] cycloaddition reactions with diazoalkanes through the molecular electron density theory

Abstract

AbstractThe strain‐promoted [3 + 2] cycloaddition (SP‐32CA) reactions of two diazoalkanes with strained dibenzocyclooctyne (DIBO) have been studied within the molecular electron density theory. Analysis of the electron localisation function of diazoalkanes allows characterising their pseudoradical structures. These pmr‐type 32CA reactions, which follow a one‐step mechanism with high asynchronicity and some polar character, have lower activation enthalpies, 11.4 and 15.4 kcal mol−1, than those with acetylene, 19.7 and 23.1 kcal mol−1, in agreement with the experimental outcomes. Analysis of the changes in electron density along the SP‐32CA reaction of phenyldiazomethane with DIBO indicates that the strain favours the depopulation of the C–C triple bond of DIBO, reducing the activation energy.