Phenol Derivatives in Ruthenium-Catalyzed C-H Arylation: A General Synthetic Access to Azole-Based Congested Polyaromatics

Design, synthesis, and evaluation of cytotoxic activities of arylnaphthalene lignans and aza-analogs

A concise and versatile synthetic strategy for the total synthesis of arylnaphthalene lignans and aza-analogs was developed. The main objective was to develop synthetic tactics for the creation of the lactone and lactam unit that would give access to an array of synthetic, natural, and/or bioactive compounds through rather simple chemical manipulation. The flexibility and potentiality of these new processes were further illustrated by the total synthesis of retrojusticidin B (13b), justicidin C (14b), and methoxy-vitedoamine A (22a). In this study, a series of novel aryl-naphthalene lignans and aza-analogs were synthesized, and the cytotoxic activities of all compounds on cancer cell growth were evaluated. The target compounds were structurally characterized by ¹ H NMR (nuclear magnetic resonance), ¹³ C NMR, infrared, high-resolution mass spectrometry, and X-ray crystallography. The IC₅₀ values of these compounds on five tumor cell lines (A549, HS683, MCF-7, SK-MEL-28, and B16-F1) were obtained by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric assay. Five of the compounds exhibited excellent activity compared to 5-fluorouracil and etoposide against the five cell lines tested, with IC₅₀ values ranging from 1 to 10 μM.

Cobalt-catalyzed, directed arylation of C–H bonds in N-aryl pyrazoles

Directed arylation of ortho C–H bonds in N-aryl pyrazoles using a cobalt catalyst is reported. Excellent tolerance of functional groups was observed.

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.

Recent Advances in C–H Bond Functionalization with Ruthenium-Based Catalysts

The past decades have witnessed rapid development in organic synthesis via catalysis, particularly the reactions through C–H bond functionalization. Transition metals such as Pd, Rh and Ru constitute a crucial catalyst in these C–H bond functionalization reactions. This process is highly attractive not only because it saves reaction time and reduces waste,but also, more importantly, it allows the reaction to be performed in a highly region specific manner. Indeed, several organic compounds could be readily accessed via C–H bond functionalization with transition metals. In the recent past, tremendous progress has been made on C–H bond functionalization via ruthenium catalysis, including less expensive but more stable ruthenium(II) catalysts. The ruthenium-catalysed C–H bond functionalization, viz. arylation, alkenylation, annulation, oxygenation, and halogenation involving C–C, C–O, C–N, and C–X bond forming reactions, has been described and presented in numerous reviews. This review discusses the recent development of C–H bond functionalization with various ruthenium-based catalysts. The first section of the review presents arylation reactions covering arylation directed by N–Heteroaryl groups, oxidative arylation, dehydrative arylation and arylation involving decarboxylative and sp3-C–H bond functionalization. Subsequently, the ruthenium-catalysed alkenylation, alkylation, allylation including oxidative alkenylation and meta-selective C–H bond alkylation has been presented. Finally, the oxidative annulation of various arenes with alkynes involving C–H/O–H or C–H/N–H bond cleavage reactions has been discussed.