Understanding the [2n+2n] reaction mechanism between a carbenoid intermediate and CO 2

BET combines topological analysis of the electron localisation function and catastrophe theory along a reaction path. This cycloaddition reaction is characterised by 16 structural stability domains, associated to the following sequence of catastrophes: C 8 H 9 NO 4 + CO 2 : 16-CF † CF † F † CFF † C † C † [FF † ]F † FCC † -0: C 9 H 9 NO 6 .

Formation of the two new C-C and C-O single bonds evolves after the transition state structure is reached. The high nucleophilic character and the electronic structure of carbenoid intermediate together with the specific approaching mode of the CO 2 molecule enable in fact the first C-C single bond formation after a very low activation enthalpy, 2.2 kcal/mol, without any external electrophilic activation. The subsequent ring closure via formation of the C-O single bond occurs at the end of the reaction.