Reaction of metal diethylnitroxides with pentafluoropyridine, pentafluorobenzene, octafluorotoluene and 2-chloro-3- or 5-nitropyridine

Article abstract of DOI:10.1016/0022-1139(95)03355-6

Treatment of the nitroxides Et2NO(1-) M(1+) (2a-c) (M = Na, Li, K) and (Et2NO(1-))2Ba(2+) (2d) with pentafluoropyridine (3) at room temperature ( 1 d) gave in all cases the compounds Py-NEt2 (8), Py-ONEt2 (9), Py-NHEt (10) and Py-O(1-)H2NEt2(1+) (11) (where Py = tetrafluoro-4-pyridyl) in the approximate ratio 1:30:30:35.The radical traps, 1,4-dinitrobenzene or galvinoxyl, retarded the reaction (5 d required for complete consumption of 3), but the same products were formed in a similar ratio and compounds 8-11 were also formed by decomposition of the amine oxide Py-N(1+)O(1-)Et2 (20) 8 (57percent); 8 + (CF3CO)2O/H2O2 -> 20 (81percent) as the monohydrate>.It is proposed that the products 8-11 arose mainly via an S_RN1 mechanism involving single electron transfer (SET) from the nitroxide 2 to the substrate 3 leading to the radical anion (21) and hence the tetrafluoro-4-pyridyl radical (22) which reacted with 2 at nitrogen to afford the amine oxide 20.Major Meisenheimer rearrangement of 20 gave hydroxylamine 9, while minor rearrangement afforded the hydroxylamine Py-N(Et)OEt (23) which eliminated ethanol to yield the secondary amine 10.Competing deoxygenation of 20 gave the tertiary amine 8 and the salt 11 was formed via decomposition of 8 in light (or on heating) involving homolytic fission of the weak N-O bond.Treatment of 9 with the acids AHF or CF3SO3H resulted in exothermic reaction and gave compounds 8 (27percent, 11percent), 10 (16percent, 18percent) and 11 (13percent, 25percent) via competing protonation at oxygen and nitrogen.The corresponding reactions of nitroxide 2a with the substrates C6HF5 (4) and C6F5CF3 (5) aforded the salt 4-H-C6F4-O(1-)H2NEt2(1+) (12) (15percent) and a mixture of the compounds 4-CF3-C6F4-R , respectively, while treatment of 2a with 2-chloro-3-nitropyridine (6) and 2-chloro-5-nitropyridine (7) gave the tertiary amines 2-N,N-diethylamino-3-nitropyridine (16) (35percent) or 2-N,N-diethylamino-5-nitropyridine (18) (25percent) together with N-(2-chloro-3-pyridyl)-N-(3-nitro-2-pyridyl)amine (17) (13percent) or N-(2-chloro-5-pyridyl)-N-(5-nitro-2-pyridyl)amine (19) (27percent) via presumed S_RN1 pathways. - Keywords: Metal diethylnitroxides; Pentafluoropyridine; Pentafluorobenzene; Octafluorotoluene; 2-chloro-3-nitropyridine; 2-chloro-5-nitropyridine