Configurations of Cycloadducts Formed in Asymmetric Intramolecular Diels–Alder Reactions

Abstract

Intramolecular cycloaddition reactions of two furfuryl fumarates yield, after crystallization, pure diastereomers of oxabicyclo[2.2.1]heptene derivatives which are versatile starting points for the total synthesis of natural products. The crystal structures of the adducts, menthyl (3aS,6R,7R,7aR)-1,3,3a,6,7,7a-hexahydro-3,3-dimethyl-1-oxo-3a,6-epoxyisobenzofuran-7-carboxylate, C 21 H 30 O5, and methyl syn-3-tert-butyl-1,3,3a,6,7,7a-hexahydro-1-oxo-3a,6-epoxyisobenzofuran-7-carboxylate, C 14 H 18 O 5 , establish the configuration at the chiral centers and provide insights into the factors controlling the diastereomeric differentiation.