Catalyst-Controlled Regiodivergent Dehydrogenative Heck Reaction of 4-Arylthiophene/Furan-3-Carboxylates

Redox-Neutral Ru(0)-Catalyzed Alkenylation of 2-Carboxaldimine-heterocyclopentadienes

A new Ru₃(CO)₁₂-catalyzed directed alkenylation of 2-carboxaldimine-heterocyclopentadienes has been accomplished. This process allows coupling of furan, pyrrole, indole, and thiophene 2-carboxaldimines with electron-poor alkenes such as acrylates, vinylsulfones, and styrenes. This regio- and chemoselective oxidative C-H coupling does not require the presence of an additional sacrificial oxidant. Density functional theory calculations allowed us to propose a mechanism and unveiled the nature of the H₂ acceptor.

Ligand-Controlled, Palladium-Catalyzed Asymmetric [4+4] and [2+4] Cycloadditions

Ligand-controlled, palladium-catalyzed asymmetric [4+4] and [2+4] cycloaddition reactions of benzofuran-derived azadienes have been developed. Taking advantage of chiral P,N-ligand (S,R_p)-PPFA, we obtained a variety of benzofuro[2,3-c][1,5] oxazocines in good yields with excellent enantioselectivities via [4+4] cycloaddition reactions. Employing chiral P,P-ligand (S)-Cl-MeO-BIPHEP, the chemo- and regioselectivities were switched to synthesize tetrahydropyran-fused spirocyclic compounds in good efficiency via [2+4] cycloaddition reactions.

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.

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.

Regioselective C-H Alkenylation and Unsymmetrical Bis-olefination of Heteroarene Carboxylic Acids with Ruthenium Catalysis in Water

An efficient weak carboxylate-assisted oxidative cross-dehydrogenative C-H/C-H coupling (CDC) of heteroarenes with readily available olefins has been devised employing water as green solvent under ruthenium(II) catalysis. The reaction is operationally simple, accommodates a large variety of heteroaromatic carboxylic acids as well as olefins, and facilitates a diverse array of high-value olefin-tethered heteroarenes in high yields (up to 87%). The potential of this ortho-C-H bond activation strategy has also been exploited toward tunable synthesis of densely functionalized heteroarenes through challenging unsymmetrical bis-olefination process in a one-pot sequential fashion. Mechanistic investigation demonstrates a reversible ruthenation process and C-H metalation step might not be involved in the rate-determining step.

Sterically Controlled C-H Olefination of Heteroarenes

The regioselective functionalization of heteroarenes is a highly attractive synthetic target due to the prevalence of multiply substituted heteroarenes in nature and bioactive compounds. Some substitution patterns remain challenging: While highly efficient methods for the C2-selective olefination of 3-substituted five-membered heteroarenes have been reported, analogous methods to access the 5-olefinated products have remained limited by poor regioselectivities and/or the requirement to use an excess of the valuable heteroarene starting material. Herein we report a sterically controlled C-H olefination using heteroarenes as the limiting reagent. The method enables the highly C5-selective olefination of a wide range of heteroarenes and is shown to be useful in the context of late-stage functionalization.

Pd-Catalyzed Intermolecular Dehydrogenative Heck Reactions of Five-Membered Heteroarenes

The Pd-mediated cross-coupling of (hetero)arenes with alkenes may be an effective method for the formation of a C–C bond from two C–H bonds. Discovered by Fujiwara and co-workers in 1967, this reaction led to a number of reports that we firstly highlighted in 2011 (review with references till June 2010) and for which, we retained the name “dehydrogenative Heck reaction”. The topic, especially the reactions of five-membered heteroarenes, has been the subject of intensive research over the last ten years. The present review is limited to these dehydrogenative Heck reactions published since 2010, underlining the progress of the procedures.

Metal-catalyzed regiodivergent organic reactions

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

Lewis base catalyzed regioselective cyclization of allene ketones or α-methyl allene ketones with unsaturated pyrazolones

A nitrogen-containing Lewis base catalyzed highly regioselective [4 + 2] cycloaddition of allene ketones or α-methyl allene ketones with unsaturated pyrazolones has been disclosed to give the corresponding tetrahydropyrano [2,3-c] pyrazoles in moderate to good yields under mild conditions. High regioselectivity, 100% atom-economy, broad substrate scope and good functional group tolerance are attractive features of this process and make it a practical and versatile transformation.

Recent advances in positional-selective alkenylations: removable guidance for twofold C–H activation

Recent advances in transition-metal catalyzed positional-selective alkenylations via twofold C–H activation directed by removable or traceless directing groups are reviewed.

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.

Recent advances in the ruthenium(ii)-catalyzed chelation-assisted C–H olefination of substituted aromatics, alkenes and heteroaromatics with alkenes via the deprotonation pathway

The transition-metal-catalyzed chelation-assisted alkenylation at the inert C–H bond of aromatics with alkenes is one of the efficient methods to synthesize substituted vinylarenes in a highly regio- and stereoselective manner.