RADICAL ION PROBES. 7. BEHAVIOR OF A HYPERSENSITIVE PROBE FOR SINGLE ELECTRON TRANSFER IN REACTIONS NOT INVOLVING ELECTRON TRANSFER

1-Methyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (8) and 1,1-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1) react with thiophenoxide ion to produce cyclopropane ring-opened products. Thermodynamic considerations effectively rule out any possibility that single electron transfer is involved in theses reactions; the process PhS- + substrate → PhS• + substrate•- is endothermic by over 50 kcal/mol! Nucleophilic attack occurs both at the least- and most-hindered carbons of the cyclopropyl group, and the product ratio (R(1°/2°) from 8 and R(1°/3°) from 1, where 1°, 2°, and 3° refer to the regioisomeric phenyl sulfides formed from these substrates) is found to vary with solvent. In dipolar, aprotic solvents, nucleophilic attack occurs preferentially at the least-hindered carbon of the cyclopropyl group (R(1°/2°) and R(1°/3°) ≈ 4−5), consistent with an SN2 mechanism. In protic solvents, products arising from nucleophilic attack at the more-substituted carbon of the cyclopropyl group become inc...