Mechanochemical Friedel-Crafts acylations

Mechanochemical Synthesis of Indene-Containing Spirolactones via Tf2O-Promoted Cascade Cyclization of 2-Benzoylbenzoic Acids with Arylalkynes

The Tf2O-promoted cascade cyclization of 2-benzoylbenzoic acids with arylalkynes was achieved under solvent-free ball-milling conditions. This process renders rapid entry to the rare indene-containing spirolactones via intramolecular cyclization of 2-benzoylbenzoic acids and subsequent annulation with arylalkynes, which resulted in one C-O and two C-C bond formations. As the reactions utilize easily available starting materials and proceed in the absence of organic solvents, the present protocol constitutes an expedient and environmentally friendly access to indene-containing spirolactones.

Acid-Solvent Cluster-Promoted General and Regioselective Friedel-Crafts Acylation with Carboxylic Acids

Carboxylic acids are considered to be the most ideal acylating reagents for Friedel-Crafts acylation. However, the low electrophilicity of carboxylic acids and the ability of their byproduct water to deactivate Lewis and Brønsted acids greatly limit their application in this reaction. In this work, we developed a general and regioselective Friedel-Crafts acylation with carboxylic acids, wherein unactivated/activated arenes and various aromatic and aliphatic carboxylic acids were viable starting materials. Key to this accomplishment is the use of trifluoromethanesulfonic acid-hexafluoroisopropanol clusters.

Ball-Milling-Enabled Nickel-Catalyzed Reductive 1,4-Alkylarylation of 1,3-Enynes under an Air Atmosphere

A ball-mill-enabled nickel-catalyzed 1,4-alkylarylation of 1,3-enynes with organic bromides has been developed, offering a versatile method for assembling tetrasubstituted allenes. This approach, the first of ball-milling-based remote radical coupling, overcomes the limitations of traditional solution-phase methods, such as the need for air- and moisture-sensitive reagents, the use of bulk solvents, and prolonged reaction times. Given the outstanding performance of ball-milling-based radical reduction coupling reactions, we anticipate further advancements in sustainable and efficient synthetic methodologies.

A fruitful century for the scalable synthesis and reactions of biphenyl derivatives: applications and biological aspects

This review provides recent developments in the current status and latest synthetic methodologies of biphenyl derivatives. Furthermore, this review investigates detailed discussions of several metalated chemical reactions related to biphenyl scaffolds such as Wurtz-Fittig, Ullmann, Bennett-Turner, Negishi, Kumada, Stille, Suzuki-Miyaura, Friedel-Crafts, cyanation, amination, and various electrophilic substitution reactions supported by their mechanistic pathways. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed. Furthermore, atropisomerism as a type of axial chirality in biphenyl molecules is discussed. Additionally, this review covers a wide range of biological and medicinal applications of the synthesized compounds involving patented approaches in the last decade corresponding to investigating the crucial role of the biphenyl structures in APIs.

The Mechanochemical Fries Rearrangement: Manipulating Isomer Ratios in the Synthesis of p-Hydroxyacetophenone at Different Scales

Herein, the first mechanochemical Fries rearrangement for the industrially important synthesis of para-hydroxyacetophenone, inside a ball mill and a twin-screw extruder, is presented. Our approach leads to a yield of 62 % in as little as 90 minutes while liquid-assisted grinding can shift the isomer ratio resulting in an excess of the desired para-product. The multigram scale-up by extrusion leads to 61 % yield in only three minutes while completely avoiding solvents. The extrusion temperature can even further be reduced by combining extrusion with a subsequent ageing step.

Cu(II)-Catalyzed Multicomponent Reaction of Pyridine Derivatives/Isoquinolines with Iodonium Ylide and 1,4-Quinones Using Mechanochemistry

An efficient copper-catalyzed solvent-free multicomponent reaction for pyridine derivatives, iodonium ylides, and 1,4-quinones is developed via a room-temperature ball milling technique. The reported protocol provides a sustainable synthesis of isoindolo[2,1-a]pyridine/isoquinoline class of molecules in good to excellent yield in a mixer mill (RETSCH MM400) engaging the commercially available copper acetate (Cu(OAc)₂) as a catalyst without the use of organic solvents. It tolerates a myriad of electron-rich and electron-deficient functionalities on the pyridine moiety. The scalability of the protocol was illustrated by successfully performing the reaction in the gram scale. The photoluminescence and related cellular study revealed that these can be used as a fluorescent chromophore-based cellular probe. A clean reaction profile and a facile experimental setup that is devoid of anhydrous reaction conditions and toxic organic solvents have established the advantages of this strategy over the reported process.

Complementarity of solution and solid state mechanochemical reaction conditions demonstrated by 1,2-debromination of tricyclic imides

The solution phase 1,2-debromination of polycyclic imides using the Zn/Ag couple was successfully transferred to solid state mechanochemical conditions. The Zn/Ag couple was replaced by the Zn/Cu couple which was prepared without any metal activation by in situ ball milling of zinc and copper dusts. The advantage of the ball milling process is that the whole procedure is operationally very simplified. The reactive alkene generated was trapped in situ by several dienes and the respective Diels-Alder cycloadducts were obtained. It was demonstrated that mechanochemical milling offers complementary conditions to solution (thermal) reaction by allowing chemical transformations to proceed which were not possible in solution and vice versa.