Structure-selectivity relationship in the cleavage of spirocyclopropyl oxindoles: An experimental and theoretical investigation.

Heterogeneous catalytic hydrogenation of strained nitrile substituted spirocyclopropyl oxindoles in acetic anhydride, allowed to the regioselective formation of ring-opened 2-oxohomotryptamines accompanied by the ring-retained spirocyclopropyl acetamides as by products. The C3single bondC9 bond fission would be induced by H atom attack via the plausible intermediacy of a stabilized benzolactam carbon-centered radical. The substituent effects on the stability of such radicals were analyzed in terms of the energy of SOMO orbitals, showing good agreement with ?m Hammett constants. The theoretical results reflect experimental findings on the reactivity of the analyzed compounds.