Molecular Dynamics Investigations of Dienolate [4 + 2] Reactions

We report quantum mechanics calculations and quasiclassical
trajectory
simulations of [4 + 2] reactions using three common dienolate substrates:
siloxy dienes, Li dienolates, and conjugated Pd enolates. Asynchronous
transition structures and unequal bond formation were invariably found,
with average time gaps of developing bonds ranging from 26.5 to >251.0
fs. The results display a spectrum of dynamically concerted and stepwise
[4 + 2] reactions, offering insights into the origin of the stereochemical
outcomes of such reactions.