Configurations of Cycloadducts Formed in Asymmetric Intramolecular Diels-Alder Reactions

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, C₂₁H₃₀O₅, and methyl syn-1,3,3a,6,7,7a-tetrahydro-3-(1,1-dimethylethyl)-1-oxo-3a,6-epoxyisobenzofuran-7-carboxylate, C₁₄H₁₈O₅, establish the configuration at the chiral centers and provide insights into the factors controlling the diastereomeric differentiation.

-1