Manganese(I) Catalyzed ortho C-H Allylation of Benzoic Acids.

The 3d-metal catalyst Mn(CO)5 Br was found to efficiently promote ortho C-H allylations of arenecarboxylates in the presence of neocuproine as the ligand. Despite the simplicity of directing group and catalyst system, the selectivity goes well beyond the state-of-the-art in that mono-allylated products are obtained exclusively with high selectivities for the least hindered ortho-position. The directing group can optionally be removed by in situ decarboxylation, opening up a regioselective entry to allyl arenes. The preparative utility of the process and its othogonality to other approaches was demonstrated by 44 products with otherwise hard-to-access substitution patterns, including 3-bromo-allylbenzene, 3-allylbenzofuran, or 5-allyl-2-methylnitrobenzene.

Photochemical Sandmeyer-type Halogenation of Arenediazonium Salts.

Trihalide salts were found to efficiently promote photochemical dediazotizing halogenations of diazonium salts. In contrast to classical Sandmeyer reactions, no metal catalysts are required to achieve high yields and outstanding selectivities for halogenation over competing hydridodediazotization. Convenient protocols are disclosed for synthetically meaningful brominations, iodinations, and chlorinations of diversely functionalized derivatives.

Rhodium-Catalyzed Annelation of Benzoic Acids with α,ß-Unsaturated Ketones with Cleavage of C-H, CO-OH, and C-C Bonds.

In the presence of a [Cp*RhCl2 ]2 catalyst, the Lewis acid In(OTf)3 , and the mild base Na2 CO3 , aromatic carboxylates and α,ß-unsaturated ketones undergo a unique hydroarylation/Claisen/retro-Claisen process to give the corresponding indanones. In this carboxylate-directed ortho-C-H annelation, the C-COR bond of the ketone and the CO-OH group of the aromatic carboxylate are cleaved, and the hydroxy group is transferred from the aromatic to the aliphatic acyl residue. This reactivity is synthetically useful, particularly when starting from cyclic ketones, which are converted into indanones bearing aliphatic carboxylate side chains, thus greatly increasing the molecular complexity of aromatic carboxylates in a single step.

ortho-C-H Arylation of Benzoic Acids with Aryl Bromides and Chlorides Catalyzed by Ruthenium.

A system consisting of catalytic amounts of [(p-cym)RuCl2 ]2 /PEt3 ⋅HBF4 , K2 CO3 as the base, and NMP as the solvent efficiently mediates the ortho-C-H arylation of benzoic acids with aryl bromides at 100 °C. Replacing the phosphine ligand with the amino acid dl-pipecolinic acid enables the analogous transformation with aryl chlorides. The key advantage of this broadly applicable transformation is the use of an inexpensive ruthenium catalyst in combination with simple carboxylates as directing groups, which can either be tracelessly removed or used as anchor points for decarboxylative ipso substitutions.

Decarboxylative Ketonization of Aliphatic Carboxylic Acids in a Continuous Flow Reactor Catalysed by Manganese Oxide on Silica.

The sustainable synthesis of long carbon chain molecules from carbon dioxide, water and electricity relies on the development of waste-free, highly selective C-C bond forming reactions. An example for such a power-to-chemicals process is the industrial-scale fermentation for the production of hexanoic acid. Herein, we describe how this product is transformed into 6-undecanone via decarboxylative ketonization using a heterogeneous manganese oxide/silica catalyst. The reaction reaches full conversion with near-complete selectivity when carried out in a continuous flow reactor, requires no solvent or carrier gas, and releases carbon dioxide and water as the only by-products. The reactor was operated for several weeks with no loss of reactivity, producing 7 kg of 6-undecanone from 10 g of catalyst and achieving a productivity of 1.135 kg per litre of reactor volume per hour. 6-Undecanone and other long-chain ketones accessible this way can be hydrogenated to industrially meaningful alkanes, or converted into valuable fatty acids via a hydrogenation/elimination/isomerizing hydrocarboxylation sequence.

Ru-Catalyzed C-H Arylation of Acrylic Acids with Aryl Bromides.

In the presence of a [Ru(p-cymene)Cl2]2/triethylphosphine/lithium carbonate catalyst system, aryl bromides undergo (Z)-selective couplings with unprotected 2-arylacrylic acids to form (Z)-diarylacrylic acids. This vinylic C-H functionalization proceeds in high yields of up to 94% and (Z/E)-ratios of up to 99:1, tolerating a wide range of functional groups. Mechanistic studies indicate that the vinylic C-H activation proceeds via base-assisted cyclometalation rather than via a Heck-type mechanism, which explains its orthogonal stereoselectivity.

Ru-Catalyzed (E)-Specific ortho-C-H Alkenylation of Arenecarboxylic Acids by Coupling with Alkenyl Bromides.

In the presence of [p-cymene)RuCl2]2, (E)-configured alkenyl bromides couple with aromatic carboxylates to form ortho-vinylbenzoic acids. This C-H vinylation proceeds in high yields without any activating phosphine ligands and has an excellent functional group tolerance. Starting from commonly available (E/Z )-mixtures of alkenyl bromides, (E)-configured vinyl arenes or dienes are formed exclusively. Mechanistic studies show that this selectivity is achieved because the (E)-configured alkenyl bromides undergo a smooth coupling, whereas the (Z)-isomers are rapidly eliminated with the formation of alkynes.