A range of oxoammonium salt-based oxidation reactions have been explored computationally using density functional theory (DFT), and the results have been correlated with experimentally derived trends in reactivity. Mechanistically, most reactions involve a formal hydride transfer from an activated C-H bond to the oxygen atom of the oxoammonium cation. Several new potential modes of reactivity have been uncovered and validated experimentally.

A scalable, high yielding, rapid route to access an array of nitriles from aldehydes mediated by an oxoammonium salt (4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate) and hexamethyldisilazane (HMDS) as an ammonia surrogate has been developed. The reaction likely involves two distinct chemical transformations: reversible silyl-imine formation between HMDS and an aldehyde, followed by oxidation mediated by the oxoammonium salt and desilylation to furnish a nitrile. The spent oxidant can be easily recovered and used to regenerate the oxoammonium salt oxidant.

We report an iodoarene-catalyzed enantioselective synthesis of β,β-difluoroalkyl bromide building blocks. The transformation involves an oxidative rearrangement of α-bromostyrenes, utilizing HF–pyridine as the fluoride source and m-CPBA as the stoichiometric oxidant. A catalyst decomposition pathway was identified, which, in tandem with catalyst structure–activity relationship studies, facilitated the development of an improved catalyst providing higher enantioselectivity with lower catalyst loadings. The versatility of the difluoroalkyl bromide products was demonstrated via highly enantiospecific substitution reactions with suitably reactive nucleophiles. The origins of enantioselectivity were investigated using computed interaction energies of simplified catalyst and substrate structures, providing evidence for both CH−π and π–π transition state interactions as critical features.

We present a new paradigm for nitroxyl-mediated processes via the merger of oxoammonium cation-mediated oxidation with visible-light photoredox catalysis. The integration of these two forms of catalysis has been realised for the oxidative amidation of aldehydes, furnishing N-acylated heterocycles. Extension of this process to the oxidative amidation of alcohols via the intermediacy of an aldehyde was successfully pursued, thus proffering a general oxidation platform. The activated amides synthesised here are excellent synthetic handles for acylation.