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■ Reaction of 3-Methylenedihydro-(3H)furan-2-one with Diazoalkanes. Syntheses and Crystal Structures of Spiranic Cyclopropyl Compounds

Christophe Roussel, Kabula Ciamala,* Joël Vebrel, Michael Knorr, and Marek M. Kubicki

*Institute of UTINAM UMR CNRS 6213, Faculty of Science and Technology, University of Franche-Comté, 16 Route de Gray, F-25030 Besançon, France

Abstract

The [3+2] cycloaddition of diphenyldiazomethane (2) (1,3-dipole) with 3-methylenedihydro-(3H)furan-2-one (5) as dipolarophile leads to the spiranic cyclopropyl derivative 1,1-diphenyl-4-oxo-5-oxaspiro[2.4]heptane (8b). Compound (8b) originates from an initially formed Δ¹-pyrazoline intermediate (7’) and subsequent rearrangement after N2 extrusion. The addition of hydroquinone to the reaction medium during the synthesis has an significant effect on the [3+2] cycloaddition yield and leads to isolation of the adduct (8a), in which hydroquinone bridges two 1,1-diphenyl-4-oxo-5-oxaspiro[2.4]heptane units through hydrogen bonds. The molecular structures of (8a,b) have been ascertained by X-Ray crystallography. In contrast, the [3+2] cycloaddition of ethyl diazoacetate (6) with the dipolarophile (5) leads to the spiranic Δ²-pyrazoline compound 3’-ethoxycarbonylspiro-Δ²-pyrazolino[5’:3]dihydro-(3H)furan-2-one (10) via a prototropic rearrangement (hydrogen shift) of an initially formed Δ¹-pyrazoline intermediate (9).