Catalyst-controlled regiodivergent C-H borylation of multifunctionalized heteroarenes by using iridium complexes

Catalyst-controlled regiodivergent C-H bond alkenylation of 2-pyridylthiophenes

A novel and effective Rh^III- and Pd^II-controlled switchable C-H alkenylation of 2-pyridylthiophenes with alkenes is realized. The alkenylation reactions proceeded smoothly in a highly regio- and stereo-selective manner to afford a broad range of C3- and C5-alkenylated products. Depending on the catalyst employed, the reactions involve two typical approaches: C3-alkenylation via chelation-assisted rhodation and C5-alkenylation via electrophilic palladation. This regiodivergent synthetic protocol was successfully applied for the straightforward building of π-conjugated difunctionalized 2-pyridylthiophenes, which may show great potential in organic electronic materials.

Photo-Induced ortho-C-H Borylation of Arenes through In Situ Generation of Rhodium(II) Ate Complexes

Photoinduced in situ "oxidation" of half-sandwich metal complexes to "high-valent" cationic metal complexes has been used to accelerate catalytic reactions. Here, we report the unprecedented photoinduced in situ "reduction" of half-sandwich metal [Rh(III)] complexes to "low-valent" anionic metal [Rh(II)] ate complexes, which facilitate ligand exchange with electron-deficient elements (diboron). This strategy was realized by using a functionalized cyclopentadienyl (Cp^A3) Rh(III) catalyst we developed, which enabled the basic group-directed room temperature ortho-C-H borylation of arenes.

Iridium-Catalysed C-H Borylation of Heteroarenes: Balancing Steric and Electronic Regiocontrol

The iridium-catalysed borylation of aromatic C-H bonds has become the preferred method for the synthesis of aromatic organoboron compounds. The reaction is highly efficient, tolerant of a broad range of substituents and can be applied to both carbocyclic and heterocyclic substrates. The regioselectivity of C-H activation is dominated by steric considerations and there have been considerable efforts to develop more selective processes for less constrained substrates. However, most of these have focused on benzenoid-type substrates and in contrast, heteroarenes remain much desired but more challenging substrates with the position and/or nature of the heteroatom(s) significantly affecting reactivity and regioselectivity. This review will survey the borylation of heteroarenes, focusing on the influence of steric and electronic effects on regiochemical outcome and, by linking to current mechanistic understandings, will provide insights to what is currently possible and where further developments are required.

Regiodivergent C-H Arylation of Triphenylene Derivatives Controlled by Electronic Effects of Diaryliodonium Salts

A regiodivergent C-H arylation of triphenylene derivatives with diaryliodonium salts was developed. The regiodivergence was controlled by electronic effects of diaryliodonium salts. When the aryl(mesityl)iodonium salts bearing strong electron-donating groups at the para-position of aryl groups were used, the arylation reactions occurred ortho to amide groups. However, if the aryl(mesityl)iodonium salts bearing electron-withdrawing groups or weak electron-donating groups at the para-position of aryl groups were utilized, the arylation reactions occurred meta to amide groups.

Ligand-free iridium-catalyzed regioselective C-H borylation of indoles

We herein report a ligand-free Ir-catalyzed C-H borylation of N-acyl protected indoles. This simple protocol could tolerate a variety of functional groups, affording C3 borylated indoles in good yields with excellent regioselectivities. We also demonstrated that the current method is amenable to gram-scale borylation and the C-B bonds could be easily converted to C-C and C-heteroatom bonds.

Catalyst-Controlled Regiodivergent C-H Alkynylation of Thiophenes*

Alkynes are highly attractive motifs in organic synthesis due to their presence in natural products and bioactive molecules as well as their versatility in a plethora of subsequent transformations. A common procedure to insert alkynes into (hetero)arenes, such as the thiophenes studied herein, consists of a halogenation followed by a Sonogashira cross-coupling. The regioselectivity of this approach depends entirely on the halogenation step. Similarly, direct alkynylations of thiophenes have been described that follow the same regioselectivity patterns. Herein we report the development of a palladium catalyzed C-H activation/alkynylation of thiophenes. The method is applicable to a broad range of thiophene substrates. For 3-substituted substrates where controlling the regioselectivity between the C2 and C5 position is particularly challenging, two sets of reaction conditions enable a regiodivergent reaction, giving access to each regioisomer selectively. Both protocols use the thiophene as limiting reagent and show a broad scope, rendering our method suitable for late-stage modification.

Mechanistic understanding enables chemoselective sp3 over sp2 C–H activation in Pd-catalyzed carbonylative cyclization of amino acids

An understanding on the factors controlling C(sp²)–H vs, C(sp³)–H selectivity in Pd-catalyzed carbonylative cyclization of γ-arylated valine derivatives has allowed to reverse the remarkable selectivity of Pd for aryl C(sp²)–H over C(sp³)–H cleavage.

A Suzuki Approach to Quinone-Based Diarylethene Photochromes

Diarylethene photochromes show promise for use in advanced organic electronic and photonic materials with burgeoning considerations for biological applications; however, these compounds typically require UV light for photoswitching in at least one direction, thus limiting their appeal. We here introduce a naphthoquinone-based diarylethene that switches between open and closed forms with visible light. The synthesis of this quinone diarylethene relies on Suzuki methodology, allowing for the inclusion of functional groups not otherwise accessible with current synthetic routes.

Hydrogen Bond Directed ortho-Selective C-H Borylation of Secondary Aromatic Amides

Reported is an iridium catalyst for ortho-selective C-H borylation of challenging secondary aromatic amide substrates, and the regioselectivity is controlled by hydrogen-bond interactions. The BAIPy-Ir catalyst forms three hydrogen bonds with the substrate during the crucial activation step, and allows ortho-C-H borylation with high selectivity. The catalyst displays unprecedented ortho selectivities for a wide variety of substrates that differ in electronic and steric properties, and the catalyst tolerates various functional groups. The regioselective C-H borylation catalyst is readily accessible and converts substrates on gram scale with high selectivity and conversion.

Metal-catalyzed regiodivergent organic reactions

This review discusses metal-catalysed regiodivergent additions, allylic substitutions, CH-activation, cross-couplings and intra- or intermolecular cyclisations.

Divergent synthesis of hydropyridine derivatives via nitrogen-containing Lewis base mediated regioselective [4 + 2] cyclizations

A nitrogen-containing Lewis base mediated regioselective [4 + 2] cyclization strategy between allenic esters and α,β-unsaturated ketimines was discovered.