Probing the Nature and Extent of Stabilization within Foiled Carbenes: Homoallylic Participation by a Neighboring Cyclopropane Ring

Oxadiazoline <b>6</b> was synthesized to generate <i>endo</i>-tricyclo­[3.2.1.0^2,4]­octan-8-ylidene (<b>3</b>) by either photolysis or thermolysis. Diastereomer <b>6a</b> thermally decomposed twice as fast as <b>6b</b>. Carbene <b>3</b> was trapped stereoselectively by acrylonitrile and diethylamine in high yields. It behaved as a nucleophilic carbene with electron-poor alkenes, like acrylonitrile, but as an electrophile with very electron-rich species, such as diethylamine. However, when the reactions were performed in cyclohexane and cyclohexene, isomerization of <b>3</b> was favored. Replacement of the double bond in 7-norbornenylidene (<b>1</b>) by the single bond in the <i>endo</i>-fused cyclopropane unit of carbene <b>3</b> led to similar outcomes. Carbene <b>3</b> rightfully belongs to the family of foiled carbenes