Dynamical Effects along the Bifurcation Pathway Control Semibullvalene Formation in Deazetization Reactions

Area of Science:

• * Computational Chemistry
• * Physical Organic Chemistry
• * Reaction Dynamics

Background:

• * The deazetization of diazo compounds is a key reaction in organic synthesis.
• * Understanding post-transition-state dynamics is crucial for predicting product distributions.
• * Previous studies often relied on minimum energy pathway calculations, potentially missing dynamic effects.

Purpose of the Study:

• * To investigate the post-transition-state dynamics of the deazetization of compound 3.
• * To elucidate the formation mechanisms of semibullvalenes 4 and 5.
• * To determine the role of dynamics versus static pathways in product selectivity.

Main Methods:

• * Density Functional Theory (DFT) calculations to map potential energy surfaces.
• * Quasi-Classical Trajectory (QCT) simulations to model reaction dynamics.
• * Analysis of kinetic isotope effects (KIEs) using isotopic substitutions.

Main Results:

• * Deazetization of 3 proceeds via a concerted pathway through an ambimodal transition state (TS1).
• * QCT simulations show that trajectories initiated from TS1 yield products 4, TS2, and 5 in a 1:1:1 ratio.
• * Newtonian kinetic isotope effects (e.g., 4:5 ≈ 1.4 for 13C1-13C2) provide evidence for dynamics-controlled product formation.

Conclusions:

• * The reaction is not solely governed by the minimum energy pathway, highlighting the importance of dynamics.
• * Product distribution is significantly influenced by the trajectory of the reacting system after the transition state.
• * This study provides unequivocal evidence for dynamics-controlled product formation in the deazetization of compound 3.