REACTION OF 3-METHYLENEDIHYDRO-(3H)FURAN-2-ONE WITH DIAZOALKANES. SYNTHESES AND CRYSTAL STRUCTURES OF SPIRANIC CYCLOPROPYL COMPOUNDS

摘要

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 A -pyrazoline intermediate (7) and/or (7') subsequent rearrangement after N_2 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 DELTA~2-pyrazoline compound 3'-ethoxycarbonylspiro-DELTA~2-pyrazolino[5':3]dihydro-(3H)furan-2-one (10) via a prototropic rearrangement (hydrogen shift) of an initially formed DELTA~1-pyrazoline intermediate (9).