tert-Butylation of Quinolinium Cations and Quinoline N-Oxides by tert-Butylmercury Halides

In the presence of t-BuHgCl/KI the radical cations formed by the addition of tert-butyl radicals to C-2 of the quinolinium cation react in Me₂SO by proton loss followed by one-electron oxidation (1a, R = H, Me, Cl). For the N-methyl, or N-methoxyquinolinium cations proton loss is not observed and the radical cations react by one-electron reduction (1b, R = Me, Cl; 1c, R = Me). With quinoline N-oxide and its 4-substituted derivatives the C-2 adduct radicals (1d, R = H, Me, Cl) are deprotonated by DABCO to yield after one-electron oxidation the 2-tert-butylquinoline N-oxides. The adduct radical cations formed by t-Bu^• addition at the C-4 of quinolinium ions 2 seldom lose the C-4 proton but react by reduction, hydration, or in the case of 2-chloroquinoline N-oxide, dimerization. The loss of the proton from the 2-adducts 1 but not from the 4-adducts 2 seems to be stereoelectronic in origin. With N-methylquinolinium cation the addition of t-Bu^• occurs selectively (>90%) at C-4 in contrast to the low selectivity observed in addition to quinolinium ion itself. However, with iV-methoxyquinolinium perchlorate the major reaction products (70-90%) result from the addition of t-Bu^• at C-2.