The [3 + 2] cycloaddition reaction between carbonyl ylides generated from epoxides and alkynes ( phenylacetylene, methyl propiolate, methyl but-2-ynoate and methyl 3-phenylpropiolate) to give substituted 2,5-dihydrofurans was investigated. The effect of indium(III) chloride on the outcome of the reaction was studied in the case of phenylacetylene and methyl propiolate. The thermal reaction between the carbonyl ylide coming from 2,2-dicyano-3-phenyloxirane and both methyl propiolate and methyl but-2-ynoate was theoretically investigated using DFT methods in order to explain the reactivity and regioselectivity observed.

International audience4-Benzoyl-3,5-diaryltetrahydrofuran-2,2-dicarbonitriles were first synthesized from 2,2-dicyano-3-aryloxiranes and chalcones at toluene reflux; the 4,5-cis products proved to be predominantly formed and were isolated. Whereas shortened reaction times were observed by using microwave irradiation or catalytic cuprous chloride, no significant stereoselectivity change was in general noticed. Reacting 2,2-dicyano-3-aryloxiranes with 2-cyclopentenone next afforded 3-aryl-4-oxohexahydro-1H-cyclopenta[c]furan-1,1-dicarbonitriles, and the endo stereoisomers were isolated. That no stereoselectivity change was noticed in the presence of cuprous chloride rather suggests an impact of the salt on the epoxide ring opening. Finally, treatment of 2,2-dicyano-3-aryloxiranes by 2-morpholinoacrylonitrile yielded 3-cyano-3-morpholino-5-phenyltetrahydrofuran-2,2-dicarbonitriles from which the preponderant trans isomers were isolated. Importantly, the molecular mechanism of the domino reaction between 2,2-dicyano-3-phenyloxirane and 2-cyclopentenone was studied. The rate-determining thermal ring opening of the oxirane is followed by a non-concerted pseudoradical-type reaction of the carbonyl ylide with 2-cyclopentenone. Using the bond evolution theory also allowed the regioselectivity of this non-polar reaction to be explained. © 2017 Elsevier B.V