Utilizing Native Directing Groups: Synthesis of a Selective IKur Inhibitor, BMS-919373, via a Regioselective C–H Arylation

Ni-Catalyzed Cyanation of (Hetero)Aryl Electrophiles Using the Nontoxic Cyanating Reagent K4[Fe(CN)6]

A Ni-catalyzed cyanation of aryl halides using potassium ferrocyanide (K4[Fe(CN)6]) as a nontoxic cyanide source has been developed. Key features of this method include the use of biphasic aqueous conditions to overcome the innate insolubility of K4[Fe(CN)6] in organic solvents and the use of a bench-stable Ni(II) precatalyst combined with a commercially available JosiPhos ligand that enhances the practicality and scalability of this cyanation reaction. The inclusion of the acidic additive tetrabutylammonium hydrogen sulfate was found to improve the reaction rate and conversion. The initial scope of this Ni-catalyzed cyanation reaction was successfully demonstrated on a range of (hetero)aryl bromides, chlorides, and sulfamates using catalyst loadings as low as 2.5 mol %. This base-metal-catalyzed methodology was further translated to the decagram synthesis of a pharmaceutical intermediate, usurping the prior Pd-catalyzed process that employed a hazardous cyanide source and solvent pair (Zn(CN)2, DMAc).

Preparative Scale Applications of C-H Activation in Medicinal Chemistry

C-H activation is an attractive methodology to increase molecular complexity without requiring substrate prefunctionalization. In contrast to well-established cross-coupling methods, C-H activation is less explored on large scales and its use in the production of pharmaceuticals faces substantial hurdles. However, the inherent advantages, such as shorter synthetic routes and simpler starting materials, motivate medicinal chemists and process chemists to overcome these challenges, and exploit C-H activation steps for the synthesis of pharmaceutically relevant compounds. In this review, we will cover examples of drugs/drug candidates where C-H activation has been implemented on a preparative synthetic scale (range between 355 mg and 130 kg). The optimization processes will be described, and each example will be examined in terms of its advantages and disadvantages, providing the reader with an in-depth understanding of the challenges and potential of C-H activation methodologies in the production of pharmaceuticals.

The cobalt(ii)-catalyzed acyloxylation of picolinamides with bifunctional silver carboxylate via C–H bond activation

The cobalt(ii)-catalyzed C–H bond acyloxylation of picolinamides with bifunctional silver carboxylate has been developed. The mild and practical esterification provides an atom-economic route to access to polysubstituted naphthalene compounds.

The application of modern reactions in large-scale synthesis

In the past decade, the field of organic synthesis has witnessed tremendous advancements in the areas of photoredox catalysis, electrochemistry, C-H activation, reductive coupling and flow chemistry. While these methods and technologies offer many strategic advantages in streamlining syntheses, their application on the process scale is complicated by several factors. In this Review, we discuss the challenges that arise when these reaction classes and/or flow chemistry technology are taken from a research laboratory operating at the milligram scale to a reactor capable of producing kilograms of product. We discuss how these challenges have been overcome through chemical and engineering solutions. Specifically, this Review will highlight key examples that have led to the production of multi-hundred-gram to kilogram quantities of active pharmaceutical ingredients or their intermediates and will provide insight on the scaling-up process to those developing new technologies and reactions.

Direct Arylation of Azoles Enabled by Pd/Cu Dual Catalysis

A practical approach toward the synthesis of 2-arylazoles via direct arylation is described. The transformation relies on a Pd/Cu cocatalyst system that operates with low catalyst loadings. The reaction conditions were found to be tolerant of a wide range of functional groups and nitrogen-containing heterocycles commonly employed in a drug discovery setting.

Late stage C-H functionalization via chalcogen and pnictogen salts

Late-stage functionalization (LSF) of heteroarenes can dramatically accelerate SAR studies by enabling the installation of functional groups that would otherwise complicate a synthetic sequence. Although heteroaryl halides and boronic esters have well-established chemistries for LSF, alternatives that enable site-selective C-H functionalization are highly attractive. Recently, three unrelated cationic groups (phosphonium, pyridinium, and thianthrenium), which can replace C-H bonds late stage, have been identified as precursors to various functional groups. This review will discuss the synthesis and application of these three salts with an emphasis on their use for LSF and application to medicinal chemistry.

Cobalt(II)-Catalyzed [4+2] Annulation of Picolinamides with Alkynes via C-H Bond Activation

A cobalt(II)-catalyzed [4+2] annulation of picolinamides with alkynes via C-H bond activation has been developed. The operationally simple annulation reaction allows for the synthesis of acyl-substituted 1H-benzoquinoline bearing multiple aromatic rings (up to 96 % yield) without co-oxidant or other oxidation factors under mild conditions. Several control experiments were carried out. This practical [4+2] annulation provides an efficient route to access highly functionalized compounds.

Utilizing Native Directing Groups: Mechanistic Understanding of a Direct Arylation Leads to Formation of Tetracyclic Heterocycles via Tandem Intermolecular, Intramolecular C-H Activation

A mechanistic study on a direct arylation using a native picolylamine directing group is reported. Kinetic studies determined the concentration dependence of substrates and catalysts, as well as catalyst degradation, which led to the development of a new set of reaction conditions capable of affording a robust kinetic profile. During reaction optimization, a small impurity was observed, which was determined to be a dual C-H activation product. A second set of conditions were found to flip the selectivity of the C-H activation to form this tetracycle in high yield. A catalytic cycle is proposed for the intermolecular/intramolecular C-H activation pathway.