On the Origins of Diastereofacial Selectivity of [4 + 2] Cycloadditions in Cage- Annulated and Polycarbocyclic Diene/Dienophile Systems

π-Facial diastereoselectivities in Diels−Alder reactions that involve π-facially differentiated cyclohexa-1,3-dienes, i.e., 3-substituted or 3−10-disubstituted hexacyclo-[10.2.1.0.2,110.4,90.4,1409,13]pentadeca-5,7-dienes have been investigated. Two types of reactions have been examined experimentally and theoretically: (i) reactions of cage-annulated, π-facially differentiated cyclohexa-1,3-dienes with π-facially symmetric dienophiles and (ii) reactions of π-facially symmetric dienes with cage-annulated, π-facially differentiated dienophiles.