Ab Initio Study of Stereo- and Regioselectivity in the Diels−Alder Reaction between 2-Phenylcyclopentadiene and α-(Methylthio)acrylonitrile

Ab initio molecular orbital calculations have been used to investigate the Diels−Alder reaction between 2-phenylcyclopentadiene and α-(methylthio)acrylonitrile. Geometry optimizations were performed with the RHF/3-21G, RHF/3-21G*, and RHF/6-31G* calculations while the correlation energy has been calculated at MP2 and MP3 levels. Four asynchronous transition structures corresponding to the formation of different stereoisomers and regioisomers associated with the four reaction channels have been located. The observed endo/exo stereoselectivity and para/meta regioselectivity are correctly described at all levels of calculation, and the calculated activation energies reflect accurately the rela…