Conformational influence on intramolecular cyclization for a β-ketoester containing oxirane ring: A theoretical and experimental study

Conformational preference for the (oxiran-2-ylmethyl 3-oxobutanoate) (11) (β-ketoester) was studied using theoretical calculation and experimental data to demonstrate the influence of the conformation on the absence of intramolecular cyclization reaction to produce butyrolactones. Transition state structure was obtained from theoretical calculation, it can be observed that the β-ketoester (CH3COCH2COO-R) moiety changes its conformation from the more stable trans-s-cis to the more energetic trans-s-trans in the transition state to acquire a suitable symmetry for the process to occur. It is therefore demonstrated theoretically and experimentally that the absence of intramolecular cyclization is due to the high energy (4.0 kcal mol−1) of the trans-s-trans conformation in comparison with the more stable conformation.