Copper-catalyzed chemoselective synthesis of 4-trifluoromethyl pyrazoles

Regioselective Synthesis of 3-Trifluoromethylpyrroles by [3 + 2] Cycloaddition of N-Acyl α-Amino Acids and 2-Bromo-3,3,3-trifluoropropene

A mild and concise method for the synthesis of 3-trifluoromethylpyrroles via base-mediated [3 + 2] cycloaddition of N-acyl α-amino acids and 2-bromo-3,3,3-trifluoropropene is described. N-Acyl α-amino acids serve as 1,3-dipole precursors without additional activating agents directly. A high level of regioselectivity was observed, regardless of the electronic nature and size of the substituents on 1,3-dipoles.

Biomacromolecule-Assisted Screening for Reaction Discovery and Catalyst Optimization

Reaction discovery and catalyst screening lie at the heart of synthetic organic chemistry. While there are efforts at de novo catalyst design using computation/artificial intelligence, at its core, synthetic chemistry is an experimental science. This review overviews biomacromolecule-assisted screening methods and the follow-on elaboration of chemistry so discovered. All three types of biomacromolecules discussed─enzymes, antibodies, and nucleic acids─have been used as "sensors" to provide a readout on product chirality exploiting their native chirality. Enzymatic sensing methods yield both UV-spectrophotometric and visible, colorimetric readouts. Antibody sensors provide direct fluorescent readout upon analyte binding in some cases or provide for cat-ELISA (Enzyme-Linked ImmunoSorbent Assay)-type readouts. DNA biomacromolecule-assisted screening allows for templation to facilitate reaction discovery, driving bimolecular reactions into a pseudo-unimolecular format. In addition, the ability to use DNA-encoded libraries permits the barcoding of reactants. All three types of biomacromolecule-based screens afford high sensitivity and selectivity. Among the chemical transformations discovered by enzymatic screening methods are the first Ni(0)-mediated asymmetric allylic amination and a new thiocyanopalladation/carbocyclization transformation in which both C-SCN and C-C bonds are fashioned sequentially. Cat-ELISA screening has identified new classes of sydnone-alkyne cycloadditions, and DNA-encoded screening has been exploited to uncover interesting oxidative Pd-mediated amido-alkyne/alkene coupling reactions.

Recent advances in pyrazole synthesis employing diazo compounds and synthetic analogues

This review summarizes the recent developments in the construction of pyrazoles using diazo compounds, nitrile imines and their synthetic equivalents.

Regioselective synthesis of 3-trifluoromethyl 1,2,4-triazoles via photocycloaddition of sydnone with CF3CN

A photocycloaddition of sydnone with CF3CN for the regioselective synthesis of 3-trifluoromethyl 1,2,4-triazoles is reported.

Synthesis of 2-trifluoromethyl chromenes via double carbonyl–ene reaction

A synthesis of 2-trifluoromethyl chromenes through double carbonyl–ene reaction of o-isopropenylphenols with trifluoroacetic anhydride is reported.

Cascade Wolff Rearrangement/Acylation: A Metal-Free and Eco-Friendly Approach for 4-Hydroxy-pyrazolo[3,4-b]pyridin-6-ones and N-Pyrazole Amides Synthesis from 5-Aminopyrazoles and α-Diazoketones

A highly chemoselective cascade Wolff rearrangement/acylation reaction between 5-aminopyrazoles and diazo compounds has been developed. The protocol can facilitate the switchable synthesis of 4-hydroxy-pyrazolo[3,4-b]pyridin-6-ones and N-pyrazole amides with the merits of a broad substrate scope, high functional group compatibility, and green and sustainable performance manner. All reactions proceeded efficiently without any catalyst and additives (acid and base) and resulted in the release of benign N₂, wherein diethyl carbonate served as a green benign solvent.

Copper-Catalyzed Synthesis of 5-Aryl-6-(Trifluoromethyl)-2,3-Dihydropyrazolo[1,2-a]Pyrazol-1(5H)-One

An efficient protocol for the synthesis of 5-aryl-6-(trifluoromethyl)-2,3-dihydropyrazolo[1,2-a]pyrazol-1(5H)-one derivatives through a copper-catalyzed [3+2]-cycloaddition of azomethine imines with 3,3,3-trifluoropropyne (generated in situ from dehydrobromination of 2-bromo-3,3,3-trifluoropropene under base conditions) is developed. The advantages of this transformation are the broad substrate scope and the good functional group compatibility. The subsequent oxidation and nucleophilic substitution/aromatization provide a new approach to 4-trifluoromethylated pyrazol-1-yl propanoic acids.

Click and Bio-Orthogonal Reactions with Mesoionic Compounds

Click and bio-orthogonal reactions are dominated by cycloaddition reactions in general and 1,3-dipolar cycloadditions in particular. Among the dipoles routinely used for click chemistry, azides, nitrones, isonitriles, and nitrile oxides are the most popular. This review is focused on the emerging click chemistry that uses mesoionic compounds as dipole partners. Mesoionics are a very old family of molecules, but their use as reactants for click and bio-orthogonal chemistry is quite recent. The facility to derivatize these dipoles and to tune their reactivity toward cycloaddition reactions makes mesoionics an attractive opportunity for future click chemistry development. In addition, some compounds from this family are able to undergo click-and-release reactions, finding interesting applications in cells, as well as in animals. This review covers the synthetic access to main mesoionics, their reaction with dipolarophiles, and recent applications in chemical biology and heterocycle synthesis.

Regioselective Synthesis of 5-Trifluoromethylpyrazoles by [3 + 2] Cycloaddition of Nitrile Imines and 2-Bromo-3,3,3-trifluoropropene

A general and practical method for the synthesis of 5-trifluoromethylpyrazoles is reported that occurs by the coupling of hydrazonyl chlorides with environmentally friendly and large-tonnage industrial feedstock 2-bromo-3,3,3-trifluoropropene (BTP). This exclusively regioselective [3 + 2] cycloaddition of nitrile imines and with BTP is catalyst-free and operationally simple and features mild conditions, high yields, gram-scalable, a broad substrate scope, and valuable functional group tolerance. Significantly, our method has been applied for the synthesis of the key intermediate of an active agonist of sphingosine 1-phosphate receptor.

Copper-catalyzed one-pot synthesis of 2-(2,2,2-trifluoroethyl)-substituted benzofused heterocycles

A method for copper-catalyzed synthesis of 2-trifluoroethyl-substituted benzofurans and indoles from the reaction of salicylaldehyde/2-aminobenzaldehyde p-tosylhydrazones with 2-bromo-3,3,3-trifluoropropene has been developed.