Ab initio study of the Diels–Alder reactions of prop-2-enethial

Abstract

The Diels–Alder reactions of prop-2-enethial with ethene, propene, methoxyethene, ethenenitrile and prop-2-enal have been examined at the MP4SDTQ/6-31G*//MP2/6-31G* level. The activation energy for the reaction with ethene is 54.48 kJ mol^–1, which is much lower than the barrier for the reactions of ethene with butadiene or prop-2-enal. The lowest barrier (32.01 kJ mol^–1) occurs in the reaction with prop-2-enal. The transition states for all of the reactions are quite similar and are synchronous, as evaluated using bond orders derived from the topological method. Application of FMO theory does predict the effect of substituent on activation barriers. There is little regioselectivity and significant endo selectivity only in the case where the dienophile is prop-2-enal.