Nickel-catalyzed amination of aryl carbamates and sequential site-selective cross-couplings

Abstract

We report the amination of aryl carbamates using nickel-catalysis. The methodology is broad in scope with respect to both coupling partners and delivers aminated products in synthetically useful yields. Computational studies provide the full catalytic cycle of this transformation, and suggest that reductive elimination is the rate-determining step. Given that carbamates are easy to prepare, robust, inert to Pd-catalysis, and useful for arene functionalization, these substrates are particularly attractive partners for use in synthesis. The sequential use of carbamate functionalization/site-selective cross-coupling processes highlights the utility of this methodology.

DFT Investigation of Suzuki–Miyaura Reactions with Aryl Sulfamates Using a Dialkylbiarylphosphine-Ligated Palladium Catalyst

“…Similarly, calculations also suggest that the barrier for oxidative addition of aryl carbamates to nickel(0) species is higher than the corresponding barrier for aryl sulfamates. 5,24 Interestingly, the product of aryl carbamate oxidative addition ( OA carb _Prod ) is endoergic by 6.5 kcal/mol in comparison to the lowest energy structure ( OA carb _1 ). Therefore, carbamate oxidative addition is both kinetically and thermodynamically disfavored, although in catalysis if the kinetic barrier for oxidative addition could be overcome the thermodynamic favorability of subsequent steps in the catalytic cycle would presumably drive the catalytic reaction.…”

Iron-Catalyzed Alkylations of Aryl Sulfamates and Carbamates

“…The methodology complements the more established methods for aryl sulfamate and carbamate functionalization achieved through arylation 7 and amination 10 processes. Considering the attractive features of sulfamate and carbamate substrates, the coupling reaction’s broad scope, and the many virtues of ironcatalysis, we expect this methodology will prove useful in multistep synthesis and will further encourage the development of iron-promoted synthetic transformations.…”

“…These substrates have recently garnered significant attention in crosscoupling reactions because of their ease of preparation, pronounced stability to a variety of reaction conditions, including conventional transition metal catalysis, and their directing group ability for arene functionalization. 7,8 Sulfamates and carbamates have primarily been used in Nicatalyzed arylation, 7,8,9 amination, 10 and deoxygenation 11 reactions, but their use in iron-catalyzed couplings holds much promise for enabling alkylative processes. No examples of iron-catalyzed sulfamate alkylation have been reported, and only a single example of a carbamate alkylation is known.…”

Nickel-Catalyzed Cross-Coupling Reactions of Unreactive Phenolic Electrophiles via C–O Bond Activation

“…Garg's group reported on a similar amination reaction of aryl carbamates [68]. Several ortho substituents in aryl carbamates were found to be tolerated, thus allowing a carbamate-directed ortho C-H functionalization followed by aminative removal of the directing group.…”