Reactions of 1- and 2-Halo- and 1,2-Dichloroadamantanes with Nucleophiles by the S(RN)1 Mechanism.
2-Bromoadamantane (2-BrAd) reacted in liquid ammonia under irradiation with diphenylphosphide (Ph(2)P(-)) ions whereas 2-chloroadamantane (2-ClAd) did not under the same experimental conditions. However, 2-ClAd yielded 2-(trimethylstannyl)adamantane in its photostimulated reaction with trimethylstannyl (Me(3)Sn(-)) ions. The compound 1-ClAd yielded the substitution product in a photostimulated slow reaction when the nucleophile is Ph(2)P(-) ion; the reaction occurs faster with the nucleophile Me(3)Sn(-) ion. All these reactions can be explained by the S(RN)1 mechanism as they did not occur in the dark and were inhibited by p-dinitrobenzene when photostimulated. In competition experiments, 1-haloadamantane showed more reactivity than 2-haloadamantane. Either with Ph(2)P(-) or Me(3)Sn(-) ions, 1-BrAd is 1.4 times more reactive than 2-BrAd while 1-ClAd is 12 times more reactive than 2-ClAd with Me(3)Sn(-) ions. In the photostimulated reaction of 1,2-dichloroadamantane (7) with Ph(2)P(-) the monosubstitution products 1-adamantyldiphenylphosphine (64%) and 2-adamantyldiphenylphosphine (15%) were formed, isolated as the oxides. From these results, it appears that when 7 receives an electron, the 1-position fragments ca. four times faster than the 2-position. The disubstitution product was not formed with Ph(2)P(-) ions, but when 7 reacted with a nucleophile having less steric bulk such as a Me(3)Sn(-) ion, the 2-chloro-1-(trimethylstannyl)adamantane and the disubstitution product 1,2-bis(trimethylstannyl)adamantane were formed. The formation of these products is explained in terms of the different rates of the electron transfer reactions of the radical anion intermediates.
Santiago
Ana N.
AN
Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, A.P. 4 - C.C. 61 - 5000 Córdoba, Argentina.
Stahl
Adriana E.
AE
Rodriguez
Gladis L.
GL
Rossi
Roberto A.
RA