Abstract
Ring closure reactions were investigated in a combined computational (density functional theory) and experimental study, to uncover the origin of diastereoselection in 5-exo-trig cyclizations of
Theory states that the favored mode of CH2 entity to adopt positions that are associated with the fewest and least severe synclinal and synperiplanar interactions. A transition structure notation is proposed based on conformational characteristics of the heterocycle, the intermediates structurally resemble the closest, i.e.
The new transition state model serves as an alternative to cyclohexane-based guidelines and adequately addresses hitherto unsettled instances properly, such as the lack in diastereoselectivity observed in the 1-phenyl-4-penten-1-oxyl radical 5-exo-trig ring closure.