On the Utilization of Nitrogen-Centered Oxidants for the Oxidation of Carbon-Carbon and Carbon-Hydrogen Bonds
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Research towards highly efficient, position-selective atom-transfer technologies is described. At the outset of this study, it was envisioned that a pendant directing group on organic substrates would direct functionalization of a vicinal position by employing one of two strategies: (1) the directing group would chelate to an early transition metal catalyst and thereby position a pendant atom-transfer agent, or (2) the directing group itself would geometrically constrain the site of C–H abstraction to dictate the site of functionalization.
Investigations into complexes of iron-cyclohexanediamine and iron-dipyrrolidine demonstrated that this class of complex was capable of affecting nitrogen-atom transfer to styrenes to produce aziridines. Utilizing sterically hindered iron complexes, limiting quantities of various styrenes could be transformed into diverse aziridines in moderate to good yields; however, due to the narrow substrate scope, the system did not allow for opportunities to evaluate position-selective, chelate-guided aziridination. Mechanistic studies provided limited support that the hypothesized iron-imido intermediate was capable of carrying out single electron oxidation of electron rich olefins but did not evidence single electron transfer from electron deficient alkenes.
Using a complementary approach, we provided the first evidence that sulfamides could direct exogenous atom-transfer processes by developing a sulfamide-guided chlorine-transfer technology. Utilizing sulfamides as masked amines, it was possible to induce g-selective chlorine transfer from N-chlorosulfamides to an appended alkyl chain, with position selectivity postulated to be a result of the elongated S–N bonds of the sulfamide motif. Quantum yield studies demonstrated that this transformation proceeded by an intermolecular radical chain propagation mechanism as opposed to an intramolecular process.
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