Cycloaddition reactions of hydrofullerenes with cyano-substituted alkenes under basic conditions

Abstract

Hydrogenated [60]fullerenes, prepared from [60]fullerene and sodium borohydride, react with alkylidenecyanoacetates [RCHCCN(CO₂Et): R = C₆H₅ (2a), 4-CH₃O–C₆H₄ (2b), 4-NO₂–C₆H₄ (2c), H (2d)] and alkylidenemalononitriles [RCHC(CN)₂: R = C₆H₅ (2e), 4-CH₃O–C₆H₄ (2f), 4-NO₂–C₆H₄ (2g), 4-(CH₃)₂N–C₆H₄ (2h)] under basic conditions to afford cyclopentenylfullerenes 3. No multi-cycloaddition products are obtained. Several bases including organic and inorganic bases can be utilized in these reactions. It is proposed that the reactions take place via the Michael addition of C₆₀H⁻, generated in situ by deprotonation of dihydrofullerene with a mild base, to the electrophilic carbon-carbon double bond of substrate 2, followed by intramolecular proton transfer and nucleophilic addition of the resulting fullerene carbanion to the nitrile group, and finally isomerization to the more stable conjugated ester or nitrile 3.