ELECTRON-TRANSFER REACTIONS - OXIDATION OF GRIGNARD-REAGENTS IN THE PRESENCE OF AN AMINOXYL AS A RADICAL-TRAPPING AGENT

The indole bisnitrone 1 (E1/2red = -0.125 V vs NHE in DMF) reacts with a series of Grignard reagents (RMgX) including primary, secondary, and tertiary alkyls and benzyl and phenyl derivatives, which show different E(OX), by single electron transfer to form C-centered radicals corresponding to the Grignard used. The radicals produced in the reaction were trapped by the (arylimino)indolinone nitroxide 5 to form the alkylated hydroxylamines 6. When the reaction is carried out with a ''cyclizing Grignard'' such as 5-hexenylmagnesium bromide, the uncyclized (5-hexen-1-yl) 6g and cyclized (methylcyclopentyl) 6h alkylated hydroxylamines are both isolated. In all cases, the Marcus theory treatment predicts high electron-transfer rate constants.