Matsuda-Heck reaction with arenediazonium tosylates in water

Synthesis and Fluorescent Properties of Alkynyl- and Alkenyl-Fused Benzotriazole-Derived α-Amino Acids

Fluorescent unnatural α-amino acids are widely used as probes in chemical biology and medicinal chemistry. While a variety of structural classes have been developed, there is still a requirement for new environmentally sensitive analogues that can closely mimic proteinogenic α-amino acids. Here, we report the synthesis and fluorescent properties of highly conjugated, benzotriazole-derived α-amino acids designed to mimic l-tryptophan. Alkynyl-substituted analogues were prepared using three key steps, nucleophilic aromatic substitution with a 3-aminoalanine derivative, benzotriazole formation via a one-pot diazotization and cyclization process, and a Sonogashira cross-coupling reaction. E-Alkenyl-substituted benzotriazoles were accessed by stereoselective partial hydrogenation of the alkynes using zinc iodide and palladium catalysis. The alkynyl analogues were found to possess higher quantum yields and stronger brightness and, a solvatochromic study with the most fluorogenic α-amino acids demonstrated sensitivity to polarity.

Straightforward and Efficient Protocol for the Synthesis of Pyrazolo [4,3-b]pyridines and Indazoles

An efficient method for the synthesis of pyrazolo [4,3-b]pyridines has been developed on the basis of readily available 2-chloro-3-nitropyridines via a sequence of SNAr and modified Japp-Klingemann reactions. The method offers a number of advantages including utilization of stable arenediazonium tosylates, operational simplicity as well as combining the azo-coupling, deacylation and pyrazole ring annulation steps in a one-pot manner. An unusual rearrangement (C-N-migration of the acetyl group) was observed and a plausible mechanism was proposed based on the isolated intermediates and NMR experiments. In addition, the developed protocol was successfully applied to the synthesis of 1-arylindazoles combining the Japp-Klingemann reaction and cyclization of the resulting hydrazone as a one-pot procedure.

Advances in deep eutectic solvents and water: applications in metal- and biocatalyzed processes, in the synthesis of APIs, and other biologically active compounds

This review highlights recent advances in metal- and biocatalyzed transformations, in the synthesis of APIs and other biologically active compounds, when employing deep eutectic solvents and water as environmentally responsible solvents.

Palladium-Catalyzed Ortho C-H Arylation of Aniline Carbamates with Diazonium Salts under Mild Conditions: Expedient Synthesis of Carbazole Alkaloids

Despite the significant progress, C-H arylation with aryldiazonium salts is a major challenge because of the faster rate of oxidative addition compared to the C-H insertion, leading to a deleterious homocoupling product. Recently, this limitation has been overcome by merging a photoredox catalyst with transition-metal catalysts which proceeds through a distinct single electron-transfer mechanism. However, we have observed that the photoredox catalyst is not necessary for the C-H arylation of aniline rather chemical reactivity can be controlled by tuning the electronic nature of the substrate. We report, herein, a palladium-catalyzed C-H arylation of aniline carbamates with aryldiazonium salts under external oxidant, acid, base free conditions at room temperature. Mechanistic studies suggest that the present reaction proceeds through a directed electrophilic metalation pathway which is the slowest step. However, the oxidative addition may take place through either ionic (2e^-) or radical (1e^-) pathway to generate hypervalent Pd(IV) or Pd(III) intermediate, respectively. A facile reductive elimination from the hypervalent palladium complex furnishes the C-H arylation product under mild conditions. The carbamate directing group is easily removed from the product to obtain the corresponding ortho-arylated aniline, which is a precursor for plethora of carbazole alkaloids and other biologically active molecules. The reaction is scaled-up to gram scale to furnish the desired product in comparable yields. Finally, we have applied this C-H arylation methodology for the synthesis of series of carbazole alkaloids such as clausine V, clauszoline K, O-methoxymahanine, and O-methylmurrayamine-D.

Ultra-fast Suzuki and Heck reactions for the synthesis of styrenes and stilbenes using arenediazonium salts as super-electrophiles

The reliable and convenient procedure for the ultrafast conversion of potassium vinyltrifluoroborate to stilbenes and styrenes with impressive TOFs is proposed.

The promoting effect of pyridine ligands in the Pd-catalysed Heck–Matsuda reaction

Simple and cheap pyridine-type ligands promote good to excellent yields for poorly efficient Pd-catalyzed Heck–Matsuda arylations in less than 1 h.