The kinetic conclusions of a recent report by Maxwell and Tsanaktsidis (J. Am. Chem. Soc. 1996, 118, 4276) were investigated. The kinetics of ring opening of the (N-butyl-2-pyrrolidinyl)methyl radical (2) to the N-butyl-4-pentenaminyl radical (1) and the reverse reaction, 5-exo cyclization of 1 to 2, were determined at 50 and 80 degrees C by competitive Bu3SnH trapping. Rate constants for 5-exo cyclization of a dialkylaminyl radical and for beta-fragmentation of a beta-(dialkylamino)ethyl radical were measured by direct laser flash photolysis (LFP) methods. In contrast to the conclusions of Maxwell and Tsanaktsidis, all of these radical reactions were facile with rate constants of at least 1 x 10(4)s(-1) . The claim by Maxwell and Tsanaktsidis that bis(tributyltin oxide) catalyzes dialkylaminyl radical reactions was investigated by LFP kinetic studies of the 5-exo cyclization of the N-methyl-5,5-diphenyl-4-pentenaminyl radical (20) in the presence of the additive which demonstrated that (Bu3Sn)(2)O does not have a catalytic effect on the reaction, Computations of the energies of the N-methyl analogs of radicals 1 and 2 with a high level of theory (fourth-order Moller-Plesset perturbation theory) and by a hybrid density functional theory with a very large basis set indicate that the cyclization reaction is expected to be slightly exergonic at 298 K. This work demonstrates that the kinetic results reported by Maxwell and Tsanaktsidis were spurious. We speculate that impurities of dichalcogens in their radical precursor samples were reduced by Bu3SnH to highly reactive chalcogen hydrides (arylthiols and benzeneselenol) in their kinetic studies.