The diastereofacial selectivity operating in Diels-Alder additions involving spirocyclic cross-conjugated cyclohexadienones with dienes of varying reactivity has been investigated. The study has included the ether series la-c as well as the lactone/ketone pair 2a/2b. In all Gases. the preferred [4+2] cycloaddition pathway consisted of bonding from that pi-surface syn to the oxygen atom. 4-Substituted-4-methyl-2,5-cyclohexadienones (monocyclic systems) were also examined and found to undergo bored formation preferentially from the face bearing the more electron-withdrawing of the two groups at than 4 position. Kinetic parameters were determined for the cycloaddition of la and 2a to cyclopentidiene. The rate acceleration profile of solvents was in the order CF3CH2OH much greater than CH(3)CNsimilar toCH(2)Cl(2) for the production of 9a from 1 a and CF3CH2OH much greater than CH2Cl2 > CH3CN for the production of 21 a from 2a, respectively. This spread in polarity had no major impact on product distribution, a phenomenon also reflected in the behavior of 4-substituted-4-methyl-2,5-cyclohexadienones under comparable conditions. Theoretical assessment of these experimental facts was undertaken at the HF/6-31 G' level. The facial selectivity is understandable in terms of the secondary interaction between the HOMO of the diene and LUMO of the dienophile as as the effective hyperconjugation between the newly forming bond and the 4-anti-C-C o-orbital due to the more electron-donating bond, as defined by the Cieplak model.