Boger, D. L.; McKie, J. A. J. Org. Chem. 1995, 60, 1271-1275.

This paper discusses the competition between tributyltin hydride and TEMPO in the reaction with an aryl iodide. Although we understand the paper primarily focuses on the TEMPO out-competing Bu₃SnH, it nonetheless sheds useful information pertaining to our mechanism. In the paper, the authors expected that the hydrogen atom abstraction by a primary radical (k~106 M^-1 s^-1) from Bu₃SnH cannot compete against the rapid coupling of the cyclization product radical with TEMPO (k~109 M^-1 s^-1). What they didn’t expect, however, was the need for 3 equivalents of Bu₃SnH. They presumed that the reason was because the generated tributyltin radical actually reacts with TEMPO, so not all of the tributyltin hydride is available to do hydrogen atom abstraction. This competing reaction resulted in unreacted starting material, and they concluded that 3 equivalents total of tributyltin hydride was required for the reaction to proceed to completion. Based on the results, we can understand why the final step in our mechanism involves the trapping of the radical by TEMPO rather than hydrogen atom abstraction by tributyltin hydride.

Three papers that cite this reference:
1. Boger, D. L.; Stauffer, F.; Hedrick, M. P. Bioorg. Med. Chem. Lett. 2001, 11, 2021-2024. (+)-CC-1065 and the duocarmycins compose a class of exceptionally potent antitumor antibiotics. Extensive efforts have been devoted to create their duplex DNA alkylation selectivity, and to establish the link between the alkylation and biological proper tie. Studies have shown that the role of attached DNA actually contributes to and is largely responsible for the DNA alkylation catalysis.
2. Jia, G.; Iida, H.; Lown, J. W. Chem. Commun. 1999, 119–120. This paper cited reference 15 in our HTML paper because its reaction also involves using TEMPO to trap a radical, and the chemistry involved is for the study of inhibitory effects against certain cells. The analogs involved in the synthesis are studied for their potency against tumor cells; similarly, the maoecrystal V synthesized in our HTML paper shows potent inhibitory activity against HeLa cells.
3. Kinney, R. J.; Jones, W. D.; Bergman, R. G. J. Am. Chem. Soc. 1978, 100, 7902. This paper is related to the chemistry in our paper because it talks about how the second part of our mechanism occurs. Our second step involves radicals forming and reacting, and this paper talks specifically about the molecules, TEMPO and Bu₃SnH, that are involved in the radical formation and trapping that occurs in the second step of our mechanism.