Catalytic effect of molecular iodine in Diels–Alder reaction: a density functional theory study

Abstract

We explore here the feasibility of employing molecular iodine as Lewis acid catalyst for Diels-Alder (DA) reaction using conceptual density functional theory (DFT) based reactivity indices and transition state analysis at the DFT (B3LYP)/6-31G(d) level of theory. Catalytic effect of iodine is probed using reactivity indices considering six different substituents for the diene at the 2-position and five different substituents at the 1-position of the olefinic dienophile. Comparison of HOMO diene-LUMO dienophile gap between the catalyzed and uncatalyzed processes confirms catalytic effect of iodine in DA reaction. Mechanistic details of both the uncatalyzed and the iodine catalyzed processes is achieved through transition state analysis for four possible stereoisomeric reactive channels with respect to isoprene-acrolein model reaction. A significant cutback in activation barrier is observed in presence of iodine. Influence of iodine on regioselectivity of the reaction and asynchronicity of bond formation is analyzed using local version of the HSAB principle and philicity index.

Mechanisms in Iodine Catalysis

“…This mechanistic proposal is further supported by computational investigations by Deuri and Phukan (Figure ) . The authors analyzed the model iodine‐catalyzed Diels–Alder reaction between isoprene and acrolein by density functional theory [B3LYP/6‐31G(d), 3–21G(d) for iodine].…”

“…45 kJ mol À1 . [51] As similarr eactions have recently also been achieved with halogen-bond catalysts, [52] it is very plausible that molecular iodine indeed acts as ah alogen-bond-based catalysti nt hese transformations.…”

“…Although the authors did not consider entropic factors and only referred to zero‐point‐corrected electronic energies, iodine significantly reduced the activation barrier for this reaction by approx. 45 kJ mol −1 …”

“… Computed transition states for the iodine‐catalyzed Diels–Alder reaction between isoprene and acrolein [B3LYP/6‐31G(d), 3–21G(d) for iodine] …”

“…[50] This mechanistic proposal is further supported by computational investigations by Deuri and Phukan ( Figure 4). [51] The authors analyzed the modeli odine-catalyzed Diels-Alder reaction between isoprene and acrolein by density functional theory [B3LYP/6-31G(d), 3-21G(d) for iodine].A lthough the authors did not consider entropicf actors and only referred to zeropoint-corrected electronic energies, iodine significantly reduced the activation barrier for this reaction by approx. 45 kJ mol À1 .…”