π-Facial Stereoselectivity in the Diels-Alder Reactions of a Rigid Carbocyclic Diene: Spiro(bicyclo(2.2.1)heptane-2,1′-(2,4) cyclopentadiene).

The plane-nonsymmetrical diene spiro(bicyclo[2.2.1]heptane-2,1′-[2,4]cyclopentadiene) (2) was synthesized, and the π-facial stereoselectivity of its Diels–Alder cycloadditions with three cyclic dienophiles was examined. Adduct ratios were very similar, and the selectivity is surmised to be mainly the result of steric interactions at the transition state. Key words: facial stereoselectivity, Diels–Alder, cycloaddition.