The utility of the PM3 method for predicting the reactivities of cyanoethenes in diels‐alder reactions with pyrrole

Abstract

The reliability of PM3 for predicting the reactivity of cyanoethenes in Diels‐Alder reactions with pyrrole was tested. Using frontier orbital theory it was predicted that the reaction is LUMO dienophile controlled, and the reaction should be facilitated in comparison to cyclopentadiene additions (pyrrole has higher HOMO energy). The transition structures were generated and compared with similar ones generated with both ab initio and PM3 calculations for cyclopentadiene additions: The geometries of the transition structures are similar, although the new CC forming bonds are 2–6% shorter, and the degree of asynchronicity is higher. The prediction of the activation barriers with the PM3 method failed totally. The preferred exo isomer in each case, indicated that the predicted stereoselectivity was incorrect. The prediction of the relative reactivity was also unreliable. Qualitative analyses of similar series of compounds can be obtained by frontier orbital energy correlations. All conclusions were made on the assumption that the reaction is concerted, which does not exclude the possibility that PM3 might be able to predict reliable reaction barriers if some other mechanisms are considered.

DFT study of the reaction proceeding in the cytidine deaminase

“…The two most up-to date computational studies of the CDA active site by Lewis et al [19,20] provide specific structures of the substrates. However, some alternative protonation states of the reaction model, which seem plausible, were not evaluated by Lewis et al, and the stationary points obtained using the semiempirical approach may not always be conclusive [21,22].…”

Benign by Design Synthesis of Novel 1H-Tetrazoles: Spectral Characterization and Antibacterial Activities

“…It has been reported that tetrazoles cover a wider spectrum of bioactive heterocycles with azapyrrole system 16,23,24 . These compounds have been used for both biological and nonbiological applications [25][26][27] . Among several types of tetrazoles, 5-amino -1-substituted derivatives have been reported as antibacterial, antiviral, anti-inflammatory and antiallergic agents [28][29][30] .…”

AM1 semiempirical study of benzopyrroles as dienes for Diels-Alder reaction

“…We recently studied theoretically the suitability of pyrrole as diene for the Diels-Alder reaction for the cycloaddition reaction (9). The predicted activation energies are too high even for the Diels-Alder reaction in the case of pyrrole acting as diene.…”