Carboxylate-assisted ruthenium(II)-catalyzed C–H arylations of 5-aryl tetrazoles: step-economical access to Valsartan

Ruthenium(II)-Catalyzed Late-Stage Incorporation of N-Aryl Triazoles and Tetrazoles with Sulfonium Salts via C-H Activation

The late-stage functionalization of active pharmaceutical ingredients is a key challenge in medicinal chemistry. Furthermore, N-aryl triazoles and tetrazoles are important structural motifs with the potential to boost the activity of diverse drug molecules. Using easily accessible dibenzothiophenium salts for the ruthenium-catalyzed C-H arylation, these scaffolds were introduced into a variety of bioactive compounds. Our methodology uses cost-efficient ruthenium, KOAc as a mild base and gives access to a plethora of highly decorated triazole and tetrazole containing drug derivatives.

Borinic Acid Catalyzed Regioselective N-Alkylation of Azoles

A method for regioselective N-alkylation of ambident, azole-type heterocycles with alkene or epoxide electrophiles is described. In the presence of diphenylborinic acid (Ph₂BOH) and an amine cocatalyst, heterocyclic nucleophiles such as 1,2,3- and 1,2,4-triazoles, substituted tetrazoles, and purine are activated toward selective N-functionalization. The scope of electrophilic partners includes enones, 2-vinylpyridine, phenyl vinyl sulfone, a dehydroalanine derivative, and epoxides. Mechanistic studies, including in situ ¹¹B NMR spectroscopy and kinetic analysis, are discussed.

Photo-Induced Ruthenium-Catalyzed C-H Arylations at Ambient Temperature

Ambient temperature ruthenium-catalyzed C-H arylations were accomplished by visible light without additional photocatalysts. The robustness of the ruthenium-catalyzed C-H functionalization protocol was reflected by a broad range of sensitive functional groups and synthetically useful pyrazoles, triazoles and sensitive nucleosides and nucleotides, as well as multifold C-H functionalizations. Biscyclometalated ruthenium complexes were identified as the key intermediates in the photoredox ruthenium catalysis by detailed computational and experimental mechanistic analysis. Calculations suggested that the in situ formed photoactive ruthenium species preferably underwent an inner-sphere electron transfer.

Solvent-free ruthenium-catalysed triflate coupling as a convenient method for selective azole-o-C-H monoarylation

Metal-catalysed ortho-directed C-H functionalization usually faces selectivity issues in the competition between mono- and disubstitution processes. We report herein the ruthenium-catalysed N-directed C-H monoarylation of arylpyrazoles with a selectivity of up to 96% or that generally reaches values above 80%. This selectivity is an effect of solvent-free conditions associated with sulfonate reagents, in the absence of frequently used acidic additives.

Combination of RuCl3·xH2O with PEG – a simple and recyclable catalytic system for direct arylation of heteroarenes via C–H bond activation

A simple and recyclable catalytic system for direct arylation of heteroarenes via C–H bond activation was developed with a relatively inexpensive RuCl₃·xH₂O as a catalyst and PEG-400 as a green medium without any additive or ligand.

Silver(i) catalyzed intramolecular cyclization of N-(2-(alk-1-yn-1-yl))-1H-tetrazoles leading to the formation of N-cyano-2-substituted indoles under ambient conditions

Synthesis of N-heterocycles from N-(2-(alk-1-yn-1-yl))tetrazoles to obtain N-cyano 2-substituted indoles as selective products.

Ru-Catalyzed C-H Arylation of Fluoroarenes with Aryl Halides

Although the ruthenium-catalyzed C–H arylation of arenes bearing directing groups with haloarenes is well-known, this process has never been achieved in the absence of directing groups. We report the first example of such a process and show that unexpectedly the reaction only takes place in the presence of catalytic amounts of a benzoic acid. Furthermore, contrary to other transition metals, the arylation site selectivity is governed by both electronic and steric factors. Stoichiometric and NMR mechanistic studies support a catalytic cycle that involves a well-defined η⁶-arene-ligand-free Ru(II) catalyst. Indeed, upon initial pivalate-assisted C–H activation, the aryl-Ru(II) intermediate generated is able to react with an aryl bromide coupling partner only in the presence of a benzoate additive. In contrast, directing-group-containing substrates (such as 2-phenylpyridine) do not require a benzoate additive. Deuterium labeling and kinetic isotope effect experiments indicate that C–H activation is both reversible and kinetically significant. Computational studies support a concerted metalation–deprotonation (CMD)-type ruthenation mode and shed light on the unusual arylation regioselectivity.

Pd(II)-catalyzed, controllable C-H mono-/diarylation of aryl tetrazoles: concise synthesis of Losartan

A palladium(II)-catalyzed C-H arylation directed by tetrazole, a metabolically stable surrogate for the carboxylic acid group in drug design, has been developed. Excellent mono-/di-selectivity was achieved through adjustment of the protecting site on the tetrazole ring. The synthetic utility of this new transformation was demonstrated in the concise total synthesis of Losartan.

Rhodium-catalyzed hydroarylation of alkynes via tetrazole-directed C–H activation

A rhodium-catalyzed hydroarylation of alkynes with aryl tetrazoles through tetrazole-directed C–H activation was developed.

Ruthenium/base-catalyzed ortho-selective C–H arylation of acylarenes with halogenated arylboronates

Ruthenium-catalyzed ortho-selective C–H arylation of acylarenes with halogenated arylboronates was promoted by the catalytic amount of bases and provided desired halogenated biaryls in excellent yields under 0.2–1 mol% ruthenium catalyst loading.

Rhodium-catalyzed olefination of aryl tetrazoles via direct C–H bond activation

Rh(iii)-catalyzed direct olefination reaction via aromatic C–H bond activation is described using tetrazole as the directing group.

K-bis(2-ethylhexyl) phosphate (BEHPK): a novel additive for C–H arylation

Use of K-bis(2-ethylhexyl) phosphate (BEHPK) as an additive enabled highly reproducible Ru-catalyzed C–H arylation under low catalyst loading (0.5 mol%).

C(sp3)-H bond arylations catalyzed by well-defined [Ru(O2CMes)2(p-cymene)]

The well-characterized ruthenium(II) biscarboxylate complex [Ru(O2CMes)2(p-cymene)] enabled versatile direct (hetero)arylations of C(sp(3))-H bonds with low (co)catalyst loading and ample substrate scope. Detailed mechanistic studies provided strong support for a facile and reversible C(sp(3))-H bond metalation.