Rhoda-Electrocatalyzed C-H Methylation and Paired Electrocatalyzed C-H Ethylation and Propylation

Electrochemical Late-Stage Functionalization

Late-stage functionalization (LSF) constitutes a powerful strategy for the assembly or diversification of novel molecular entities with improved physicochemical or biological activities. LSF can thus greatly accelerate the development of medicinally relevant compounds, crop protecting agents, and functional materials. Electrochemical molecular synthesis has emerged as an environmentally friendly platform for the transformation of organic compounds. Over the past decade, electrochemical late-stage functionalization (eLSF) has gained major momentum, which is summarized herein up to February 2023.

Transition Metal-Catalyzed C-H Functionalization Through Electrocatalysis

Electrochemically promoted transition metal-catalyzed C-H functionalization has emerged as a promising area of research over the last few decades. However, development in this field is still at an early stage compared to traditional functionalization reactions using chemical-based oxidizing agents. Recent reports have shown increased attention on electrochemically promoted metal-catalyzed C-H functionalization. From the standpoint of sustainability, environmental friendliness, and cost effectiveness, electrochemically promoted oxidation of a metal catalyst offers a mild, efficient, and atom-economical alternative to traditional chemical oxidants. This Review discusses advances in the field of transition metal-electrocatalyzed C-H functionalization over the past decade and describes how the unique features of electricity enable metal-catalyzed C-H functionalization in an economic and sustainable way.

Paired Electrolysis Enabled Cyanation of Diaryl Diselenides with KSCN Leading to Aryl Selenocyanates

The first example of paired electrolysis-enabled cyanation of diaryl diselenides, with KSCN as the green cyanating agent, has been developed. A broad range of aryl selenocyanates can be efficiently synthesized under chemical-oxidant- and additive-free, energy-saving and mild conditions.

Ruthenium-Catalyzed Monoselective C-H Methylation and d 3-Methylation of Arenes

Site-selective installation of C-Me bonds remains a powerful and sought-after tool to alter the chemical and pharmacological properties of a molecule. Direct C-H functionalization provides an attractive means of achieving this transformation. Such protocols, however, typically utilize harsh conditions and hazardous methylating agents with poor applicability toward late-stage functionalization. Furthermore, highly monoselective methylation protocols remain scarce. Herein, we report an efficient monoselective, directed ortho-methylation of arenes using N,N,N-trimethylanilinium salts as noncarcinogenic, bench-stable methylating agents. We extend this protocol to d ₃-methylation in addition to the late-stage functionalization of pharmaceutically active compounds. Detailed kinetic studies indicate the rate-limiting in situ formation of MeI is integral to the observed reactivity.

Silver-Free C-H Activation: Strategic Approaches towards Realizing the Full Potential of C-H Activation in Sustainable Organic Synthesis

The activation of carbon-hydrogen bonds is considered as one of the most attractive techniques in synthetic organic chemistry because it bears the potential to shorten synthetic routes as well as to produce complementary product scopes compared to traditional synthetic strategies. However, many current methods employ silver salts as additives, leading to stoichiometric metal waste and thereby preventing the full potential of C-H activation to be exploited. Therefore, the development of silver-free protocols has recently received increasing attention. Mechanistically, silver can serve various roles in C-H activation and thus, avoiding the use of silver requires different approaches based on the role it serves in a given process. In this Review, we present the comparison of silver-based and silver-free methods. Focusing on the strategic approaches to develop silver-free C-H activation, we provide the reader with the means to develop sustainable methods for C-H activation.

Facilitating Rh-Catalyzed C-H Alkylation of (Hetero)arenes and 6-Arylpurine Nucleosides (Nucleotides) with Electrochemistry

An electrochemical approach to promote the ortho-C-H alkylation of (hetero)arenes via rhodium catalysis under mild conditions is described. This approach features mild conditions with high levels of regio- and monoselectivity that tolerate a variety of aromatic and heteroaromatic groups and offers a widely applicable method for late-stage diversification of complex molecular architectures including tryptophan, estrone, diazepam, nucleosides, and nucleotides. Alkyl boronic acids and esters and alkyl trifluoroborates are demonstrated as suitable coupling partners. The isolation of key rhodium intermediates and mechanistic studies provided strong support for a rhodium(III/IV or V) regime.