Quantum chemical studies on the mechanistic aspects of tandemsequential cycloaddition reactions of cyclooctatetraene with ester andnitrones
The mechanisms of the tandem sequential [4þ2]/[3þ2] and [3þ2]/[4þ2] cycloaddition sequencesinvolving an ester, cyclooctatetraene (COTE), and cyclic and acyclic nitrones for the formation of a diverserange of isoxazolidine derivatives and other synthetic precursors are reported. A thorough exploration ofthe PES has characterized several regio-, stereo- and enantio-selective mechanistic channels involved inthese reactions. A perturbation molecular orbital (PMO) analysis been employed to rationalize the re-sults. It has also been found that the initial electrocyclic ring closure of the COTE is the rate-determiningstep in the tandem sequential [4þ2]/[3þ2] addition sequence. The thermolytic breakdown of thetandem adducts to subsequent monocyclic, bicyclic and tricyclic adducts occurs generally with very highactivation barriers making it an inconvenient synthetic approach. The different reactivity of all the threedouble bonds present in the dipolarophile is reported. Finally, the mechanistic possibilities of [3þ2]/[4þ2] addition sequences involving the same reaction components in the case of cyclic and acyclicnitrones are explored extensively. The results suggest a novel and convenient routes for obtainingproducts of high selectivity with less energetic requirements. In some instances, new cycloadductshitherto unreported are obtained.
An article published by Elsevier Inc. and also available at https://doi.org/10.1016/j.jmgm.2019.06.019
Isoxazolidines, Mechanistic stud, Tandem addition, Cyclooctatetraene, Nitrones
E. Opoku et al. / Journal of Molecular Graphics and Modelling 92 (2019) 17e31. https://doi.org/10.1016/j.jmgm.2019.06.019