Visible-Light-Induced C4-Selective Functionalization of Pyridinium Salts with Cyclopropanols.

The site-selective C-H functionalization of heteroarenes is of considerable importance for streamlining the rapid modification of bioactive molecules. Herein, we report a general strategy for visible-light-induced ß-carbonyl alkylation at the C4 position of pyridines with high site selectivity using various cyclopropanols and N-amidopyridinium salts. In this process, hydrogen-atom transfer between the generated sulfonamidyl radicals and O-H bonds of cyclopropanols generates ß-carbonyl radicals, providing efficient access to synthetically valuable ß-pyridylated (aryl)ketones, aldehydes, and esters with broad functional-group tolerance. In addition, the mild method serves as an effective tool for the site-selective late-stage functionalization of complex and medicinally relevant molecules.

Nickel-Catalyzed Double Dehydrogenative Coupling of Secondary Alcohols and ß-Amino Alcohols To Access Substituted Pyrroles.

Herein, we demonstrate the first nickel-catalyzed double dehydrogenative condensation of secondary alcohols and ß-amino alcohols in one pot to the pyrrole derivatives. A series of 2,5- and 2,3,5-substituted pyrroles were obtained in ≤83% yield, releasing water and hydrogen gas as byproducts. Initial mechanistic studies, including defined Ni catalyst, deuterium labeling experiments, quantitative determination of hydrogen gas evaluation, and detection of water generation in the reaction mixture, were performed.

Iron-Catalyzed Coupling of Methyl N-Heteroarenes with Primary Alcohols: Direct Access to E-Selective Olefins.

An efficient Fe-catalyzed system is reported for direct α-olefination of methyl-substituted N-heteroarenes with primary alcohols. The catalytic dehydrogenative coupling enables a series of functionalized E-olefinated N-heteroaromatics with excellent selectivity (>99%). Initial mechanistic studies including deuterium-labeling experiments provide evidence for the participation of the benzylic C-H/D bond of alcohols.

Nickel-catalysed direct α-olefination of alkyl substituted N-heteroarenes with alcohols.

Catalytic α-olefination of alkylheteroarenes with primary alcohols via dehydrogenative coupling is presented. A simple nickel catalyst system stabilised by readily available nitrogen ligands enables a series of interesting E-configured vinylarenes (confirmed by X-ray crystal-structure analysis) to be synthesised in good to excellent yields with olefin/alkane selectivity of >20 : 1. Hydrogen and water are generated as byproducts and quantitative determination of H2 was performed.

Nickel-Catalyzed Alkylation of Ketone Enolates: Synthesis of Monoselective Linear Ketones.

Herein we have developed a Ni-catalyzed protocol for the synthesis of linear ketones. Aryl, alkyl, and heteroaryl ketones as well as alcohols yielded the monoselective ketones in up to 90% yield. The catalytic protocol was successfully applied in to a gram-scale synthesis. For a practical utility, applications of a steroid derivative, oleyl alcohol, and naproxen alcohol were employed. Preliminary catalytic investigations involving the isolation of a Ni intermediate and defined Ni-H species as well as a series of deuterium-labeling experiments were performed.

Nickel-catalysed alkylation of C(sp3)-H bonds with alcohols: direct access to functionalised N-heteroaromatics.

The first base-metal catalysed coupling of primary alcohols with methyl-N-heteroaromatics is reported. The use of an earth abundant and nonprecious NiBr2/L1 system enables access to a series of C(sp3)-alkylated N-heteroaromatics. Mechanistic studies have established the participation of a hydrogen-borrowing strategy for α-alkylation.

Nickel-Catalyzed Hydrogen-Borrowing Strategy for α-Alkylation of Ketones with Alcohols: A New Route to Branched gem-Bis(alkyl) Ketones.

The α-alkylation of ketones using an earth-abundant and nonprecious NiBr2/L1 system is reported. This nickel-catalyzed reaction could be performed in gram scale and successfully applied in the synthesis of donepezil (Alzheimer's drug) and functionalization of steroid hormones and fatty acid derivatives. Synthesis of N-heterocycles, methylation of ketones, and one-pot double alkylation to bis-hetero aryl ketones using two different alcohols with a single catalyst broadens the scope of the catalytic protocol. Preliminary mechanistic studies using defined Ni-H species and deuterium-labeling experiments established the participation of the borrowing-hydrogen strategy.

Palladium(ii)-catalyzed direct O-alkenylation of 2-arylquinazolinones with N-tosylhydrazones: an efficient route to O-alkenylquinazolines.

An efficient Pd(ii)-catalyzed direct O-alkenylation of 2-arylquinazolinones with simple ketone-derived N-tosylhydrazones is reported. In this reaction, O-alkenylquinazolines were obtained in good yields, with excellent functional group tolerance. Pd-carbene migratory insertion is proposed as the key step in the reaction mechanism.