Understanding the puzzling chemistry of bicyclo[2.1.0]pentane.

Three thermal reactions of bicyclo[2.1.0]pentane have been studied by CASPT2-g3 and CASSCF electronic structure calculations. They are isomerization to cyclopentene, isomerization to 1,4-pentadiene, and cycloaddition to fumaronitrile. All three of these reactions exhibit unusual features that have prompted mechanistic debate. The present computational results provide a basis for understanding the experimental observations.

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