Azetidines. 5. Reaction of 1,1,3,3-Tetramethyl- and 1-Benzyl-1,3,3-trimethylazetidinium Ions with Butyllithium and Phenyllithium. Deuterium Labeling as a Mechanistic Probe

Article abstract of DOI:10.1021/jo01300a046

The reactions of 1,1,3,3-tetramethylazetidinium iodide (1) and 1-benzyl-1,3,3-trimethylazetidinium bromide (7) with butyllithium and with phenyllithium were studied in ether.The products from the reaction of 1 with butyllithium were 1,3,3-trimethylpyrrolidine (2), 3,3-dimethyl-4-(methylamino)-1-butene (3), 1-(dimethylamino)-2,2-dimethylheptane (4), neopentylpyrrolidine (5), and 1-(dimethylamino)-2,2-dimethylcyclopropane (6).With phenyllithium, 1 gave 2 and 1-(dimethylamino)-2,2-dimethyl-3-phenylpropane (11).With butyllithium, 7 gave 2-phenyl-1,4,4-trimethylpyrrolidine (8), 1-benzyl-3,3-dimethylpyrrolidine (9), and 1-neopentyl-2-phenylpyrrolidine (10).The reaction of phenyllithium with 7 gave only 8 and 9.Mechanistic information was obtained by labeling 1 with deuterium in three different ways: N-methyl-d₃, 2,2-d₂, and N-methyl-d₃-2,2-d₂.A primary kinetic isotope effect of 9.4 was found for the formation of 2 from 1-N-methyl-d₃.When 2 was formed from 1-2,2-d₂, a secondary kinetic isotope effect of 1.17 was measured.The formation of 4 from 1-2,2-d₂ was accompanied by a primary kinetic isotope effect of 4.7, suggesting a carbene intermediate.Ylide carbanions involving decomposition to a carbene carbanion in the formation of 3 and an azomethine ylide in the formation of 5 and 9 are probable intermediates.It is postulated that the azomethine ylides react with ethylene formed from the reaction of butyllithium with the solvent ether by means of a concerted (4 + 2) cycloaddition reaction.A primary kinetic isotope effect of 20 was found for the formation of pentylbenzene from dibenzyldimethylammonium bromide and butyllithium.