Reduction of substituted nitro compounds with tri-n-butyltin hydride

Abstract

α-Substituted nitro compounds have been reduced with tri-n-butyltin hydride to give replacement of the α-substituent by hydrogen (2-bromo-, 2-chloro- and 2-nitro-2-phenylsulphonylpropane to 2-nitropropane; p-nitrobenzyl chloride, bromide, iodide and thiocyanate to p-nitrotoluene; 5-nitrofurfuryl nitrate to 2-methyl-5-nitrofuran and 2-hydroxymethyl-5-nitrofuran; 2-(bromomethyl)-1-metbyl-5-nitroimidazole to 1,2-dimethylimidazole). 2-Bromo-2-nitrohept-6-ene and 1-bromo-1-nitrohex-5-ene were reduced to 2-nitrohept-6-ene and 1-nitrohex-5-ene, 5-bromo- and 5-phenylsulphonyl-5-nitro-6-phenyl-norborn-6-ene to 5-nitro-6-phenylnorborn-6-ene and 2-iodo-2-nitro-3-(endo-norborn-2-en-5-yl)propane to 2-nitro-3-(endo-norborn-2-en-5-yl)propane without cyclisation of the intermediate alkenyl α-nitroalkyl radicals. 2-Bromo-2-nitrohex-5-eneand 1 -bromo-1 -, nitropent-4-ene were reduced to the respective nitroalkenes at high [Bu₃SnH] but at lower [Bu₃SnH] cyclisation to 1-methyl-1-nitrocyclopentane and 1-nitrocyclopentane took place. Inhibition studies of the reductions of 2-bromo-2-nitrohex-5-ene and p-nitrobenzyl bromide showed a radical chain mechanism. In some of the reductions at low [Bu₃SnH], radical rearrangement of the intermediate α-nitroalkyl radicals gave the respective ketones. Mechanisms involving (a) addition/elimination and (b) dissociation of intermediate radical anions, are proposed.