Cyclobutane-bicyclobutane system-I. The relative reactivity of the central bond in bicyclobutanecarbonitrile and the double bond in crotononitrile in nucleophilic reactions

The ease of nucleophilic cleavage of the central bond of bicyclo[1.1.0]butanecarbonitrile 1 by alkoxides was compared to that of the double bond in crotononitrile 2. With both MeO^- /MeOH and i-PrO^-/PrOH, 2 reacts faster than 1 (by a factor of ca. 8 and 3 respectively). Analysis of the activation parameter reveals that in MeO^-/MeOH, both substrates have about the same activation energy and the reaction rate of 1 is markedly retarded by entropy effect. In i-PrO-/i-PrOH the entropy of activation is in favour of the reaction of 1 white its activation energy is higher than that of 2. Considering the steric and electronic effects of the substituents, it is concluded that the central bond of bicyclobutanecarbonitrile is more susceptible to nucleophilic attack than the analogous double bond.