A computational examination of Diels–Alder reactions with 1,3-cyclopentadienes bearing anionic and cationic substituents at C-5

Ab initio calculations predict that deprotonation and protonation of 5-heterosubstituted 1,3-cyclopentadienes would significantly modify their facial selectivities in Diels–Alder additions. Anionic substituents enhance syn-addition, and cationic substituents promote anti-addition, relative to the neutral dienes. Stereoelectronic and steric effects together determine the facial selectivity of ionic dienes.