Stereochemistry of the Diels–Alder reaction: steric effects of the dienophile on endo-selectivity

Abstract

Structures are assigned to adducts of cyclopentadiene with αβ-unsaturated nitriles, ketones, and esters. Product ratios are determined for series of dienophiles which differ in their position of alkyl substitution relative to the double bond. In each series increased size of the alkyl group enhances the endo-selectivity of that group. This effect is attributed to non-bonding repulsive interactions in the transition state.