Metal triflates–methanesulfonic acid as new catalytic systems: application to the Fries rearrangement

Metabolic, toxicological, chemical, and commercial perspectives on esterification of dietary polyphenols: a review

Molecular modifications have been practiced for more than a century and nowadays they are widely applied in food, pharmaceutical, or other industries to manipulate the physicochemical, bioactivity, metabolic/catabolic, and pharmacokinetic properties. Among various structural modifications, the esterification/O-acylation has been well-established in altering lipophilicity and bioactivity of parent bioactive compounds, especially natural polyphenolics, while maintaining their high biocompatibility. Meanwhile, various classic chemical and enzymatic protocols and other recently emerged cell factory technology are being employed as viable esterification strategies. In this contribution, the main motivations of phenolic esterification, including the tendency to replace synthetic alkyl phenolics with safer alternatives in the food industry to improve the bioavailability of phenolics as dietary supplements/pharmaceuticals, are discussed. In addition, the toxicity, metabolism, and commercial application of synthetic and natural phenolics are briefly introduced. Under these contexts, the mechanisms and reaction features of several most prevalent chemical and enzymatic esterification pathways are demonstrated. In addition, insights into the studies of esterification modification of natural phenolic compounds and specific pros/cons of various reaction systems with regard to their practical application are provided.

Specific-Ion Effects Unveil a Route for Modulating Oxidatively Triggered Acid Systems for Reservoir Applications

On-demand in situ preparation of industrially relevant organic acids, namely, methanesulfonic acid, triflic acid, and trifluoroacetic acid, is demonstrated in this study. Sodium and potassium bromate were found to selectively oxidize a series of ammonium salts NH₄X, where X = OMs, OTf, or OTFAc, with characteristic clock reaction behavior. The redox system undergoes rapid acid formation following an extended induction time at 150 °C and is identified as a potential candidate for high-temperature oil field chemistry applications where on-demand acid placement is required. Although the reaction kinetics for acid formation from NH₄X salts where X = Cl, Br, F, or SO₄^2- follows a pK_a trend, the rates of formation of the organic acids are much slower and deviate from this trend. Furthermore, we demonstrate that the rate of acid formation can be modulated by the addition of alkali metal salts, with the strongest effect observed from LiBr. Spectroscopic studies implicate the formation of lithium bromate ion pairs that slow or altogether inhibit the oxidation of NH₄⁺. Additionally, the presence of Br^- alters the reaction path, eliminating the clock behavior and creating a pathway for Li⁺ to strongly inhibit the redox reaction. From these studies, a method for slowing ammonium oxidation under reservoir conditions to sufficiently delay acid formation until the precursors are placed in the zone of interest is identified.

Fries-type rearrangement of acylanilides in the presence of ytterbium triflate

Ytterbium triflate has been used to catalyse the Fries-type rearrangement of various acylanilides with moderate yields when lithium perchlorate was used as co-catalyst.

Tartaric Acid–Zinc Nitrate as an Efficient Brønsted Acid-Assisted Lewis Acid Catalyst for the Mannich Reaction

Tartaric acid–zinc nitrate has been found to be an efficient Brønsted acid-assisted Lewis acid catalytic system for the facile synthesis of β-amino carbonyl compounds through the one-pot Mannich reaction of aldehydes, aromatic amines and ketones in ethanol at room temperature. Remarkable enhancement of reactivity by tartaric acid (Brønsted acid) was observed in these reactions in the presence of anhydrous zinc nitrate (Lewis acid), due to coordination of the tartaric acid ligand to zinc ions increasing the acidity of the system. This procedure shows some advantages such as mild reaction conditions, short reaction times and high yields.

New applications for bismuth(III) salts in organic synthesis: from bulk chemicals to steroid and terpene chemistry

Bismuth(III) salts are currently considered efficient and "ecofriendly" reagents and catalysts for the development of new applications in organic synthesis. The preparation of bismuth(III) triflate and its analogues is reviewed as well as some of their applications to the synthesis of bulk chemicals via electrophilic addition and cyclization reactions. The use of bismuth(III) salts in the development of new chemical processes involving steroids and terpenes as substrates is also discussed.

Applications of bismuth(III) compounds in organic synthesis

This review article summarizes the applications of bismuth(III) compounds in organic synthesis since 2002. Although there are an increasing number of reports on applications of bismuth(III) salts in polymerization reactions, and their importance is acknowledged, they are not included in this review. This review is largely organized by the reaction type although some reactions can clearly be placed in multiple sections. While every effort has been made to include all relevant reports in this field, any omission is inadvertent and we apologize in advance for the same (358 references).

Fries Rearrangement of Aryl Formates: A Mechanistic Study by Means of 1H, 2H, and 11B NMR Spectroscopy and DFT Calculations

1H, 2H, and 11B NMR spectroscopy has been used to study the mechanism of the Fries rearrangement of aryl formates promoted by boron trichloride by monitoring both the substrate and the Lewis acid. DFT calculations were employed to investigate the energetics of several reaction paths and to calculate NMR chemical shifts of key intermediates and products. After the formation of a 1:1 substrate-Lewis acid adduct, the rearrangement proceeds in two steps, beginning with the cleavage of the ester bond and the release of formyl chloride in situ, which, in turn, acts as a formylating agent, introducing an aldehydic functionality into the aromatic ring. The high regioselectivity (only the ortho product is obtained) is also accounted for by the proposed intermolecular, Lewis acid-assisted mechanism.

Convergent Synthesis of Complex Diketopiperazines Derived from Pipecolic Acid Scaffolds and Parallel Screening against GPCR Targets

A convergent approach to highly functionalized diketopiperazines (DKPs) using enantioenriched pipecolic acids is described. Scandium triflate-catalyzed [4 + 2] aza-annulation was employed to produce stereochemically well-defined building blocks. A resin "catch and release" strategy was devised to convert annulation products to pipecolic acid monomers. Complex diketopiperazines were efficiently assembled utilizing one-pot cyclodimerization of pipecolic acids. Massively parallel screening of the complex DKPs against a panel of molecular targets identified novel ligands for a number of G-protein-coupled receptors (GPCRs).