Electron transfer photochemistry of 7-(spirocyclopropane)quadricyclane: capture of a radical cation and sequential cyclopropylcarbinyl rearrangements

Abstract

The electron transfer photo-sensitized reaction of 7-(spirocyclopropane)quadricyclane (1) with methanol produces two rearranged mono-methanol adducts, 2 and 3, and a bis-methanol adduct, 4. The products reveal that 1 ᭹ + reacts by stereo-and regiospecific attack of methanol on one trisubstituted cyclopropane ring. The resulting free radical rapidly undergoes one or two (consecutive) cyclopropylcarbinyl to butenyl rearrangements. The mono-adducts are formed by net hydrogen abstraction, the di-adduct via a (secondary) electron transfer reaction of 3.

The Protoadamantane Radical Cation

“…[1,2] The removal of an electron from bonding molecular orbitals of saturated hydrocarbons gives so-called σ-radical cations: [3Ϫ9] a species characterized by partially broken σ CϪC and/or σ CϪH bonds. [10] Structural elucidations of such species are challenging both experimentally [4,6,8] and computationally, [11Ϫ21] due to facile rearrangements and the open-shell character of the respective wavefunctions. Even the qualitative results sensitively depend on the level of theory employed, especially for highly symmetrical hydrocarbons, which typically undergo JahnϪTeller distortions [22] (exceptions are known [23] ) upon ionization.…”