Photooxidative set initiated N-demethylation of N,N'-dimethylanlines: Mimicking the cytochrome P-450 type oxygenations

Alkali-Driven Photoinduced N-Dealkylation of Aryl Tertiary Amines and Amides

By extending the photoinduced oxidative mechanism of aryl tertiary amines proposed earlier to an alkaline environment based on the prediction of quantum mechanics computations and the validation of meticulous experiments, we discovered a photoinduced oxidative N-dealkylation method for both aryl tertiary amines and amides. The dealkylation was achieved in an alkaline environment under mild conditions accompanied by excellent functional group tolerance.

Photoinduced Nickel-Catalyzed Selective N-Demethylation of Trialkylamines Using C(sp2)-Bromides as HAT Reagents

N-Demethylation of trialkylamines is a useful transformation, but typically requires harsh reaction conditions and stepwise procedures, as well as judicious protection of labile functional groups. Herein we report a mild, catalytic approach for the demethylation of trialkylamines by utilizing photoinduced nickel catalysis wherein C(sp2)-bromides serve as hydrogen-atom transfer (HAT) reagents. This method achieves direct demethylation of trialkylamines with wide functional group compatibility, making it highly suitable for late-stage derivatization of complex molecules. Mechanistic investigations provide evidence that C(sp2) radicals generated via photoinduced Ni-C(sp2) bond homolysis are involved in hydrogen atom abstraction from trialkylamines. Utilizing steric control of the C(sp2)-bromides, our HAT approach achieves demethylation with excellent site selectivity in the presence of benzyl-substituted amines, which is complementary to the selectivity of classical approaches that afford debenzylation product instead.

N-Dealkylation of Amines

N-dealkylation, the removal of an N-alkyl group from an amine, is an important chemical transformation which provides routes for the synthesis of a wide range of pharmaceuticals, agrochemicals, bulk and fine chemicals. N-dealkylation of amines is also an important in vivo metabolic pathway in the metabolism of xenobiotics. Identification and synthesis of drug metabolites such as N-dealkylated metabolites are necessary throughout all phases of drug development studies. In this review, different approaches for the N-dealkylation of amines including chemical, catalytic, electrochemical, photochemical and enzymatic methods will be discussed.

Minimization of Back-Electron Transfer Enables the Elusive sp3 C-H Functionalization of Secondary Anilines

Anilines are some of the most used class of substrates for application in photoinduced electron transfer. N,N-Dialkyl-derivatives enable radical generation α to the N-atom by oxidation followed by deprotonation. This approach is however elusive to monosubstituted anilines owing to fast back-electron transfer (BET). Here we demonstrate that BET can be minimised by using photoredox catalysis in the presence of an exogenous alkylamine. This approach synergistically aids aniline SET oxidation and then accelerates the following deprotonation. In this way, the generation of α-anilinoalkyl radicals is now possible and these species can be used in a general sense to achieve divergent sp3 C-H functionalization.

Palladium-catalyzed amination of aryl nonaflates

The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of ligands 2-4 and 6 allows for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. With use of Xantphos 5, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkylamine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions.

Photoinduced demethylation of 4-nitro-N,N-dimethylaniline

The title compound (3) upon photoexcitation becomes demethylated by either an external acceptor in benzene or the methoxide ion in methanol. The triplet state of 4-nitroaniline (1), 4-nitro-N-methylaniline (2), 3 and the 3-nitro analogue (4) in solution at room temperature was characterized by time-resolved UV-vis spectroscopy. The triplet state of 3 in benzene reacts with other nitroarenes, such as nitrobenzene and nitronaphthalenes, by demethylation, yielding eventually 2 and further products. This quenching reaction is close to the diffusion-controlled limit. The conversion of 3 into 2 is accompanied by a permanent bleaching at 370-400 nm within 10 its and the quantum yield is up to 0.3, this being in agreement with the quantum yield of intersystem crossing. An intermediate with peaks at 420 and 700 nm is attributed to a C-centered radical: H2*C(CH3)N-C6H4-NO2, which is also involved with 3 in methanol in the presence of methoxide. The overall H-atom transfer takes place within a few micros. Another electron transfer reaction, involving the non-absorbing alpha-aminoethyl radical, occurs from triethylamine to the triplet state of 3. The observed transient with a maximum at 330 nm in benzene or acetonitrile is assigned to the conjugate acid of the radical anion of 3 which subsequently disproportionates in the ms range. The photochemical properties of 1-4 and the mechanisms of the demethylation and reduction reactions are discussed.