Micelle enabled C(sp2)-C(sp3) cross-electrophile coupling in water via synergistic nickel and copper catalysis

Amine-Borane-Mediated, Nickel/Photoredox-Catalyzed Cross-Electrophile Coupling between Alkyl and Aryl Bromides

Nickel/photoredox catalysis has emerged as a powerful platform for exploring nontraditional and challenging cross-couplings. Herein, a metallaphotoredox catalytic protocol has been developed on the basis of a tertiary amine-ligated boryl radical-induced halogen atom transfer process under blue-light irradiation. A wide variety of aryl and heteroaryl bromides featuring different functional groups and pharmaceutical moieties were facilely coupled to rapidly install C(sp3)-enriched aromatic scaffolds. The compatibility of Lewis base-ligated borane with nickel catalysis was well exemplified to extend the chemical space for Ni-catalyzed cross-electrophile coupling.

Electrochemically Driven para-Selective C(sp2)-H Alkylation Enabled by Activation of Alkyl Halides without Sacrificial Anodes

With alkyl halides (I, Br, Cl) as a coupling partner, an electrochemically driven strategy for para-selective C(sp2)-H alkylation of electron-deficient arenes (aryl esters, aldehydes, nitriles, and ketones) has been achieved to access diverse alkylated arenes in one step. The reaction enables the activation of alkyl halides in the absence of sacrificial anodes, achieving the formation of C(sp2)-C(sp3) bonds under mild electrolytic conditions. The utility of this protocol is reflected in high site selectivity, broad substrate scope, and scalable.

Implementation of micelle-enabled C(sp2)-C(sp3) cross-electrophile coupling in pharmaceutical synthesis

A sustainable C(sp2)-C(sp3) cross-electrophile coupling was developed between readily available 5-bromophthalide and 1-benzyl-4-iodopiperidine under micellar conditions, leading to a key intermediate of one of our development compounds. Copper was found to play a crucial role as a co-catalyst in this dual catalysis system. The chemistry and process were successfully demonstrated in a kilo scale to deliver sufficient drug substance to the clinical campaigns. This is the first reported scale-up of such a challenging cross-electrophilic coupling that uses an aqueous medium, and not undesirable reprotoxic polar aprotic solvents (e.g. DMF, DMAc, and NMP).

Aqueous micellar technology: an alternative beyond organic solvents

Solvents are the major source of chemical waste from synthetic chemistry labs. Growing attention to more environmentally friendly sustainable processes demands novel technologies to substitute toxic or hazardous solvents. If not always, sometimes, water can be a suitable substitute for organic solvents, if used appropriately. However, the sole use of water as a solvent remains non-practical due to its incompatibility with organic reagents. Nonetheless, over the past few years, new additives have been disclosed to achieve chemistry in water that also include aqueous micelles as nanoreactors. Although one cannot claim micellar catalysis to be a greener technology for every single transformation, it remains the sustainable or greener alternative for many reactions. Literature precedents support that micellar technology has much more potential than just as a reaction medium, i.e., the role of the amphiphile as a ligand obviating phosphine ligands in catalysis, the shielding effect of micelles to protect water-sensitive reaction intermediates in catalysis, and the compartmentalization effect. While compiling the powerful impact of micellar catalysis, this article highlights two diverse recent technologies: (i) the design and employment of the surfactant PS-750-M in selective catalysis; (ii) the use of the semisynthetic HPMC polymer to enable ultrafast reactions in water.

Palladium-Catalyzed Cross-Electrophile Coupling between Aryl Diazonium Salt and Aryl Iodide/Diaryliodonium Salt in H2O-EtOH

We report herein a mild highly chemoselective palladium-catalyzed cross-electrophile coupling between readily accessible aromatic diazonium salt and aryl iodide or diaryliodonium salt in water-ethanol (2:1) medium. Mechanistic studies revealed that ethanol is crucial to generate an active Pd(0) catalyst, and the counterion of the diazonium salt renders a cationic Pd(II) species that facilitates subsequent oxidative addition to aryl iodide/diaryliodonium salt. Silver(I) salt was crucial to retain the catalytic activity of palladium, removing the iodide ion as a precipitate.

Visible-Light Enabled C(sp3)-C(sp2) Cross-Electrophile Coupling via Synergistic Halogen-Atom Transfer (XAT) and Nickel Catalysis

We herein report the first visible-light-mediated cross-coupling of unactivated alkyl iodides with aryl bromides through synergistic halogen atom transfer (XAT) and nickel catalysis. This simple protocol operates under mild reaction conditions and tolerates a variety of functional groups affording C(sp³)-C(sp²) cross-coupling products in good to moderate yields.