Stereochemistry of the Diels–Alder reaction: effect of diene structure on endo-selectivity

Abstract

Structures are assigned to adducts of cyclohexa-1,3-diene and spiro[2,4]hepta-1,3-diene with a number of dienophiles. Product ratios are determined, results are compared with reactions of cyclopentadiene, and it is concluded that the major steric interaction which controls endo-selectivity is that between substituents of the dienophile and the methylene hydrogens of cyclopentadiene and of cyclohexa-1,3-diene, and the methylene group of spiro[2,4]hepta-1,3-diene.