Stereochemical Control in the Intramolecular Diels-Alder Reaction. 2. Structural and Electronic Effects on Reactivity and Selectivity

Article abstract of DOI:10.1021/ja00368a020

The cylization reactions of a series of triene lactones activated by electron-withdrawing groups at the terminus of the chain have been investigated.The 4 + 2 cycloadducts resulting from intramolecular Diels-Alder cycloaddition were characterized and the stereochemistry determined.The effects of varying the structure of the electron-withdrawing groups and the substitution patterns of the dienophile on the rate and stereoselectivity were examined.In all cases studied, trans-hydrindene systems were produced exclusively, although the rates of the cyclization varied dramatically.This effect was interpreted on the basis of steric inhibition of resonance in the dienophile.The effects of geminal substitution in the connecting chain were also examined, and it was found that the stereochemical outcome was not altered but a rate enhancement of ca. 4* occurred, presumably due to a decrease in the ΔS<*> for cyclization.This effect was interpreted in terms of a buttressing due to the geminal substitution which favorably influenced the population of conformers properly disposed to undergo cycloaddition.