Reactions of 1,3-Dihaloadamantanes with Carbanions in DMSO: Ring-Opening Reactions to Bicyclo[3.3.1]nonane Derivatives by the S(RN)1 Mechanism.
The reactions of 1,3-dihaloadamantanes with various carbanionic nucleophiles were studied. Potassium enolates of acetophenone (2) and pinacolone (10b) and the anion of nitromethane (10a) reacted with 1,3-diiodoadamantane (1a) in DMSO under photostimulation by a free radical chain process to form a 1-iodo monosubstitution product as an intermediate, which undergoes concerted fragmentation to form derivatives of 7-methylidenebicyclo[3.3.1]nonene (3 and 11). This reaction does not occur in the dark at 25 degrees C, and the photostimulated reaction is partially inhibited by p-dinitrobenzene. 1,3-Dibromoadamantane (1b) and 1-bromo-3-chloroadamantane (1c) also reacted under irradiation with 2, although more sluggish than 1a, also giving the 7-methylidenebicyclo[3.3.1]nonene derivative 3. When a nucleophile was used without acidic hydrogens in the alpha-position, such as the enolate ion of isobutyrophenone (16), in order to inhibit the ring opening of adamantane, it reacted under irradiation with 1a to give the products adamantane, 1-iodoadamantane, monosubstituted 17, 1-iodo-monosubstituted 19, and disubstituted 20. Their distribution depended on the experimental conditions. In these reactions, 1-iodoadamantane and 19 were intermediates. For reactions involving the radical anion intermediate of the 1-iodo monosubstitution product, the intermolecular ET to the substrate was observed to be much faster than intramolecular ET to the C-I bond.
Lukach
Andrés E.
AE
Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, A.P. 4, C.C. 61, 5000 Córdoba, Argentina.
Santiago
Ana N.
AN
Rossi
Roberto A.
RA