Carbon radical addition to N-sulfonylimines mediated by triethylborane or zinc

Dearomative Alkylation of Heteroarenium Salts via Blue Light Enabled Homolytic C-C Bond Cleavage

Alkyl substituted nitrogen heterocycles are important building blocks in drug molecules, agrochemicals, and materials. Herein we report a simple and efficient way to prepare such compounds by coupling alkyl halides with heteroarenium salts. Detailed experimental and computational studies indicate that this reaction goes through a radical coupling and avoids the formation of undesired homocoupling of heteroarenium salts via recycling such dimers through C-C bond cleavage under blue light.

Modular synthesis of α-branched secondary alkylamines via visible-light-mediated carbonyl alkylative amination

The development of methods for the assembly of secondary α-alkyl amines remains a central challenge to chemical synthesis because of their critical importance in modulating the physical properties of biologically active molecules. Despite decades of intensive research, chemists still rely on selective N-alkylation and carbonyl reductive amination to make most amine products. Here we report the further evolution of a carbonyl alkylative amination process that, for the first time, brings together primary amines, aldehydes and alkyl iodides in a visible-light-mediated multicomponent coupling reaction for the synthesis of a wide range of α-branched secondary alkylamines. In addition to exploring the tolerance and limitations in each reaction component, we also report preliminary applications to the telescoped synthesis of α-branched N-heterocycles and an N-alkylation protocol that is selective for primary over cyclic secondary amines. Our data support a mechanism involving addition of an alkyl radical to an uncharged alkyl imine which, to the best of our knowledge, has not previously been described. We believe that this method will enable practitioners of synthetic chemistry in academic and industrial settings to approach the synthesis of these important molecules in a manner that is streamlined compared to established approaches.

Excited-state palladium-catalysed reductive alkylation of imines: scope and mechanism

Palladium catalysis induced by visible-light irradiation is a promising tool for promoting unusual chemical reactivity. Here, the hybrid alkyl radical/Pd(i) species generated is used to promote the reductive alkylation of imines.

Synthesis of amino-diamondoid pharmacophores via photocatalytic C-H aminoalkylation

We report a direct C-H aminoalkylation reaction using two light-activated H-atom transfer catalyst systems that enable the introduction of protected amines to native adamantane scaffolds with C-C bond formation. The scope of adamantane and imine reaction partners is broad and deprotection provides versatile amine and amino acid building blocks. Using readily available chiral imines, the enantioselective synthesis of the saxagliptin core and rimantadine derivatives is also described.

Photoredox-Catalyzed Multicomponent Petasis Reaction with Alkyltrifluoroborates

A redox-neutral alkyl Petasis reaction has been developed that proceeds via photoredox catalysis. A diverse set of primary, secondary, and tertiary alkyltrifluoroborates participate effectively in this reaction through a single-electron transfer mechanism, in contrast to the traditional two-electron Petasis reaction, which accommodates only unsaturated boronic acids. This protocol is ideal to diversify benzyl-type and glyoxalate-derived aldehydes, anilines, and alkyltrifluoroborates toward the rapid assembly of libraries of higher molecular complexity important in pharmaceutical and agrochemical settings.

Radical Addition to N-Tosylimines via C-H Activation Induced by Decatungstate Photocatalyst

A method for the radical addition toward N-tosylimines based on light promoted C-H activation by tetrabutylammonium decatungstate is described. The reaction proceeds under irradiation using 400 nm light emitting diodes in conventional glassware. The method can be applied for alkylations (cycloalkanes, ethers, dimethylformamide) and acylation (primary aliphatic aldehydes) of both aromatic and aliphatic N-tosylimines.

Mild, Redox-Neutral Alkylation of Imines Enabled by an Organic Photocatalyst

An operationally simple, mild, redox-neutral method for the photoredox alkylation of imines is reported. Utilizing an inexpensive organic photoredox catalyst, alkyl radicals are readily generated from the single-electron oxidation of ammonium alkyl bis(catecholato)silicates and are subsequently engaged in a C–C bond-forming reaction with imines. The process is highly selective, metal-free, and does not require a large excess of the alkylating reagent or the use of acidic additives.