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

Post-transition-state dynamics during the deazetization of 3 resulting in two degenerate semibullvalenes ( 4 and 5 ) have been investigated with density functional theory (DFT) and quasi-classical trajectory (QCT) calculations. Removal of N 2 from 3 occurs through a synchronous and concerted pathway through an ambimodal transition-state ( TS1 ). In addition to TS2, the exclusively anticipated product from minimum energy pathway (MEP) calculations, trajectories initiated from TS1 produce 4, TS2, and 5 in 1:1:1 ratio. Isotopic substitutions ( 12 C( 13 C/ 14 C)-H(D) at 1–2 positions) result in purely Newtonian kinetic isotope effects ( 4: 5 ≈ 1.4 for 13 C 1 – 13 C 2 ), an unequivocal evidence for dynamics controlled product formation.