Pathway Bifurcation in the (4 + 3)/(5 + 2)-Cycloaddition of Butadiene and Oxidopyrylium Ylides: The Significance of Molecular Orbital Isosymmetry

Abstract

By drawing analogies from the dimerization of cyclopentadiene, a novel reaction pathway bifurcation is uncovered in the cycloaddition of oxidopyrylium ylides and butadiene. Analysis of the potential energy surface (at the M06-2X/6-311+G(d,p) level of theory) in combination with Born−Oppenheimer molecular dynamics simulations (M06-2X/6-31+G(d)) demonstrate that both the (4 + 3)-and (5 + 2)-cycloaddition products are accessed from the same transition state. Key indicators of a pathway bifurcation (asynchronous bond formation, and a second transition state for the interconversion of the products) are also observed. The absence of a post-transition state bifurcation in the related oxidopyridinium systems of Krenske and Harmata is rationalized. Finally, the isosymmetry of the oxidopyrylium and cyclopentadiene molecular orbitals as well as the presence of "secondary orbital interactions" are emphasized as the common source of nonstatistical behavior. Application of these principles will allow for the rapid identification of new reaction pathway bifurcations.

Mechanistic investigations on Pinnick oxidation: a density functional theory study

“…Secondly, proton transfer from chlorous acid represents the first-half pathway, from the pre-reaction complex until the TS, with a noticeable change of the bond length near TS. Due to significant differences between the progressions of the two bond formations O-H and C-O in the TS 8, it would be valuable to get more validations on PES towards the chronological formation of these bonds from the point of molecular dynamic (MD) simulations, especially the behaviour of the system within time (figure 8) (for the molecular dynamics on transition state structures see: [60][61][62][63][64][65][66]). Classical MD calculations were carried out on one trajectory, where the forward and backward propagation of TSs are initiated in the region of the PES near the TS (t = 0 fs) showing the typical reactive bonds toward intermediate 9 and reactants (acrylaldehyde and chlorous acid).…”

Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization Initiation Proceeds with Two-Electron Reductive Cleavage

“…Quasiclassical trajectory molecular dynamics (QCTMD) simulations were utilized to understand the chronological character for formation of first C⎼C bonds in the HETD and HOMD (Figure 7). [61][62][63][64][65][66][67] The QCTMD simulations were carried out using the PROGDYN program, 68 in the whole trajectory once formed although for a small proportion of trajectories the C3⎼C4 distance oscillates in the range between 1.6 Å and 2.0 Å. By recording the timing for the C3⎼C4 distance to be shortened below 1.6 Å, we obtained the average timing for the first C⎼C bond formation at 43.0 and 47.0 fs for HETD 8 + and HOMD 11 + , respectively.…”

Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization Initiation Proceeds with Two-Electron Reductive Cleavage

“…Quasiclassical trajectory molecular dynamics (QCTMD) simulations were utilized to understand the chronological character for formation of first C⎼C bonds in the HETD and HOMD (Figure 7). [62][63][64][65][66][67][68] The QCTMD simulations were carried out using the PROGDYN program, 69 in the whole trajectory once formed although for a small proportion of trajectories the C3⎼C4 distance oscillates in the range between 1.6 Å and 2.0 Å. By recording the timing for the C3⎼C4 distance to be shortened below 1.6 Å, we obtained the average timing for the first C⎼C bond formation at 43.0 and 47.0 fs for HETD 8 + and HOMD 11 + , respectively.…”