Synthesis and ethylene-promoted metathesis of adducts of tandem [4+2]/[4+2] cycloaddition between bis-furyl dienes and maleic acid derivatives

During this work, a series of 1,4:5,8-diepoxynaphthalenes, annellated with various carbo- and heterocycles, was synthesized based on the tandem intermolecular/intramolecular [4+2] cycloaddition of bis-furyl dienes with moderately to highly reactive cyclic dienophiles (maleic anhydride and maleinimides). The stereochemistry of the resulting adducts was established using 2D NMR and X-ray structural analysis, which showed that both successive Diels–Alder reactions led to single diastereoisomers of the target cycloadducts corresponding to the exo-transition state. The resulting hexacyclic compounds represent original polyfunctional synthons suitable for subsequent transformations, which has been demonstrated by the example of the ethylene-promoted ROCM reaction under new types of second-generation Hoveyda–Grubbs catalysts comprising a coordination N → Ru bond in a six-membered ring. As a result, the metathesis products, unsaturated 4,7-epoxyisobenzofurans, were obtained in satisfactory yields.