Synlett

Heteroatom-based olefinating reagents (e.g., organic phosphonates, sulfonates, etc.) are used to transform carbonyl compounds into alkenes, and their mechanism of action involves aldol-type addition, cyclization, and fragmentation of four-membered ring intermediates. We have developed an analogous process using ethyl 1,1,1,3,3,3-hexafluoroisopropyl methylmalonate, which converts electrophilic aryl aldehydes into α-methylcinnamates in up to 70% yield. The reaction plausibly proceeds through the formation of β-lactone that spontaneously decarboxylates under the reaction conditions. The results shed light on the Knoevenagel–Doebner olefination, for which decarboxylative anti-fragmentation of aldol-type adducts is usually considered.

Carboxymethyl C5-functionalized pyridine-oxazoline (PyOx) ligands are immobilized onto Merrifield and Wang resins utilizing three distinct strategies. The immobilized PyOx ligands are employed in the Pd-catalyzed heterogeneous Heck–Matsuda reaction for the desymmetrization of 3-cyclopenten-1-ol, resulting in the production of 20 examples of aryl-penten-1-ols with yields reaching up to 87%, and enantiomeric ratios ranging between 90:10 and 99:1. These outcomes align with those achieved by the homogeneous counterparts, demonstrating comparable efficiency. Subsequent recycling analysis reveals a progressive decline in catalyst efficiency upon reuse, suggesting the formation of palladium black on the catalyst surface.

We report improved protocols for the synthesis of thiazolium precatalysts from primary amines, carbon disulfide, and α-halo ketones. For N-alkyl-substituted derivatives, yields of the corresponding thiazolethiones can be dramatically improved by isolating the intermediate dithiocarbamates. In most cases, meta-chloroperbenzoic acid can advantageously replace H2O2 in acetic acid for the oxidation of thiazolethiones into thiazoliums. This approach was applied to the synthesis of a thiazolium featuring a 2-adamantyl N-substituent, the corresponding persistent carbene, and its dimer.

Functionalized 1,2,4,5-tetrasubstituted benzenes are synthetically difficult or laborious to access. The Rh-catalyzed [2+2+2] cycloaddition of a diyne and internal alkyne offers a seemingly straightforward route to these scaffolds; however, this has been largely restricted to alkynes bearing activating (coordinating) functional groups, with very few examples of unactivated alkynes. In this work, we disclose an assessment of Rh-catalyzed [2+2+2] cycloadditions employing unactivated internal alkynes, focusing on the structural diversity and compatibility of both alkyne and diyne components. The limitations of this method are disclosed, with exceptionally bulky alkynes and specific functional groups undergoing side reactions. Furthermore, the practicalities of gram-scale reactions and catalyst recovery/reuse are demonstrated.

We have developed a TfOH-catalyzed, highly efficient protocol for the synthesis of biologically active β-acylamino ketones from aldehyde, ketone, and nitrile by avoiding the use of acetyl chloride. The reaction proceeds through a sequential aldol reaction followed by a nucleophilic attack of nitrile and hydrolysis of nitrile in one pot. The attractive features of this tandem process are mild reaction conditions, high atom economy, broad substrate scope with 51–87% yield, gram-scale reaction, and ease of operation.

Azo compounds with a high density, high enthalpy, and excellent detonation performance have received increasing research attention. The conventional method of chemical dehydrogenation that is used to form azo compounds involves the use of strong oxidants, resulting in environmental pollution. Electrochemical organic synthesis is considered an old method and a new technology. In this work, azofurazan tetrazole {H2AzFT; 5,5′-[diazene-1,2-diylbis(1,2,5-oxadiazole-4,3-diyl)]bis-1H-tetrazole} and azofurazan hydroxytetrazole (H2AzFTO) were synthesized by a green and efficient electrochemical dehydrogenation coupling of 5-(4-aminofurazan-3-yl)-1H-tetrazole and 5-(4-aminofurazan-3-yl)-1-hydroxytetrazole, respectively. The structures of H2AzFT and (NH4)2AzFTO were fully characterized by infrared spectroscopy, nuclear magnetic resonance, and elemental analysis, and their thermal stabilities were determined by differential thermal analysis.

A simple, economical, and safe method for the synthesis of mesoionic 1,3-diaryltetrazolium derivatives bearing a para-substituted phenyl group at the 1- or 3-position via thiosemicarbazides was established. Such compounds were directly obtained from the corresponding para-substituted anilines instead of aryl isothiocyanates and arylhydrazines. The newly synthesized mesoionic compounds were successfully converted into the corresponding nitrosotetrazolium salts, which were utilized as catalysts for oxidation of an aliphatic alcohol and analyzed by cyclic voltammetry to determine the correlation between the catalytic efficiencies and redox potentials. The proposed method can be widely applied and is valuable for investigating the substituent effects in mesoionic and related compounds.

Herein, we report the synthesis of functionalized three-dimensional benzophenone analogues derived from [2.2]paracyclophane (pCp). The potential use of these compounds as photocatalysts is disclosed. Benzophenone and its derivatives are well-known photoactive compounds that have been extensively employed over the years as catalysts to promote a variety of transformations activated by light. The development of differently substituted three-dimensional versions of such compounds may significantly expand the range of their applications in photocatalysis. Exploitation of the planar chirality of substituted paracyclophanes may also lead to significant innovations in different fields. [2.2]Paracyclophane-based benzophenone derivatives incorporating reactive ester or amide functions at their pseudo-gem position are successfully prepared in a selective manner. Examples of both racemic and enantiopure compounds are reported. As a proof of concept, the catalytic activities of the newly synthesized molecules are compared to that of benzophenone in a known photooxidation reaction.

The electrophilic thiolation of alkenes initiated by DMTSM and the addition of CF3SO2Na in one pot has been developed. This reaction also can be extended to ArSO2Na. This protocol features a good substrate scope, simple procedures, and mild reaction conditions and affords the desired products in moderate yields without metal catalysts.

Over the past years our lab has established a research program towards the late-stage introduction of deuterium into organic molecules using Pd-catalyzed reversible C–H activation as a means to affect hydrogen isotope exchange. Through catalyst design, including the introduction of novel ligand scaffolds, as well as the use of strategically chosen optimization and screening approaches, e.g., exploiting microscopic reversibility by first optimizing de-deuteration processes or using a multi-substrate screening approach, our studies have resulted in a number of synthetically useful labelling protocols and are described herein from a personal perspective.1 Introduction2 β-C(sp3)–H Deuteration of Free Carboxylic Acids3 Nondirected C–H Deuteration of Arenes4 Nondirected C–H Deuteration of Heteroarenes5 Conclusion