Identifying reactive normal modes and their effect on regioselectivity in Myers-Saito and Schmittel cyclization of enyne-allenes: a combined perspective between the reaction force constant and statistical tools.

This paper presents a theoretical study on the distinguishable regiodivergent C-C Myers-Saito and C-C Schmittel routes of benzannelated enyne-allene cycloaromatizations, in which substitutions on the terminal alkyne by alkyl (-CH, -CHCH, -CH(CH) and -C(CH)) and aryl (-CH and -CH(CH)) groups were included. Mechanistic differences were found between substituents attached to alkynes with and without α-H, whereas in the former the Schmittel cyclization proceeds together with 1,8-H migration, in the latter it does so as the sole primitive event. It was also observed that bulky substituents preferentially favor the C-C Schmittel route, and the statistical prediction of regioselectivity is greatly affected when the ratio of accessible vibrational microstates of the transition states is included, especially in highly competing routes, , ΔΔ → 0.

Reaction force constant as a descriptor of the principle of non-perfect synchronization.

Context: In this study, a small set of 1,3-dipolar cycloaddition reactions that proceed at the same exothermicity is presented. Our main objective was to extend the application of the reaction force constant concept to gain an understanding of the reactivity principles. Inspired by a recent article where we show that the Bell-Evans-Polanyi principle is fulfilled under the condition of an equal degree of (a)synchronicity, here, we demonstrate that the reaction force constant is also a suitable descriptor to quantify the principle of non-perfect synchronization proposed by Bernasconi as a way to understand deviations from the Bell-Evans-Polanyi principle.