At room temperature (25°C), the Diels-Alder cycloaddition between cyclopenta-1,3-diene and 1H-pyrrole-2,5-dione predominantly yields the endo-adduct product. However, when the reaction is carried out at an elevated temperature of 90°C, the major product obtained is the exo isomer instead. Further investigations revealed that the initially formed endo isomer undergoes isomerization to the more stable exo isomer at 90°C.
Based on the given information, which stereoisomeric form of the Diels-Alder adduct would you anticipate to be predominantly formed at room temperature? Provide a rationale to justify why this particular isomer is generally the favored product.