Phosphine-Catalyzed [3 + 2] Cycloaddition Reaction of α-Diazoacetates and β-Trifluoromethyl Enones: A Facile Access to Multisubstituted 4-(Trifluoromethyl)pyrazolines

Recent highlights in the synthesis and biological significance of pyrazole derivatives

Aza-heterocyclic scaffolds are privileged cores in the composition of their potential therapeutic profiles and versatile synthetic intermediates. Pyrazole is one of the frequently studied compounds of "azole" family and consists of nitrogen in a 1,2 linking sequence. These motifs possess a wide-spectrum of applications in the field of pharmaceuticals, agrochemicals, polymer chemistry, cosmetics, food industries and more. In addition, functionalized pyrazole derivatives are frequently used as ligands in coordination chemistry and metal-catalysed reactions. As exemplified by numerous recent reports, pyrazoles are highly promising pharmacophores with excellent therapeutic applications. Owing to their aromaticity, the ring structures have many reactive positions, where electrophilic, nucleophilic, alkylation and oxidative reactions might occur. The structural adroitness and diversity of pyrazole cores further emanated numerous fused bicyclic skeletons with various biological applications. In this review, we highlight the recent synthetic methods developed for the preparation of functionalized pyrazole derivatives (From 2017 to present). In addition, we have also covered the notable biological activities (anti-cancer, anti-inflammatory, anti-bacterial and anti-viral) of this ubiquitous core. Herein, we emphasised the synthesis of pyrazoles from variety of precursors such as, alkynes, α,β-unsaturated carbonyl compounds, diazo reagents, nitrile imines, diazonium salts, 1,3-dicarbonyl compounds and etc. Moreover, the recent synthetic methodologies focusing on the preparation of pyrazolines and pyrazolones and variously fused-pyrazoles are also included. Authors expect this review could significantly help the researchers in finding elegant novel tools to synthesize pyrazole skeletons and expand their biological evaluation.

Stereoselective Synthesis of Polysubstituted Conjugated Dienes Enabled by Photo-Driven Sequential Sigmatropic Rearrangement

We here reported a highly stereoselective method for the synthesis of polysubstituted conjugated dienes from α-aryl α-diazo alkynyl ketones and pyrazole-substituted unsymmetric aminals under mild conditions, which was promoted by photo-irridation and involved with 1,6-dipolar intermediate and quadruple sigmatropic rearrangements, was successfully developed. In this transformation, the cleavage of four bonds and the recombination of five bonds were implemented in one operational step. This protocol provided a modular tool for constructing dienes from amines, pyrazoles and α-alkynyl-α-diazoketones in one-pot manner. The results of mechanistic investigation indicated that the plausible reaction path underwent the 1,6-sigmatropic rearrangement instead of the 1,5-sigmatropic rearrangement.

Theoretical Study on the Copper-Catalyzed ortho-Selective C-H Functionalization of Naphthols with α-Phenyl-α-Diazoesters

The aromatic C(sp2)-H functionalization of unprotected naphthols with α-phenyl-α-diazoesters under mild conditions catalyzed by CuCl and CuCl2 exhibits high efficiency and unique ortho-selectivity. In this study, the combination of density functional theory (DFT) calculations and experiments is employed to investigate the mechanism of C-H functionalization, which reveals the fundamental origin of the site-selectivity. It explains that CuCl-catalyzed ortho-selective C-H functionlization is due to the bimetallic carbene, which differs from the reaction catalyzed by CuCl2 via monometallic carbene. The results demonstrate the function of favourable H-bond interactions on the site- and chemo-selectivity of reaction through stabilizing the rate-determining transition states in proton (1,3)-migration.

Synthesis of 2-Pyrazolines with a CF3- and Alkyne-Substituted Quaternary Carbon Center via [3 + 2] Cycloaddition of β-CF3-1,3-enynes and Diazoacetates

Given the importance of both the CF₃ group and the alkyne moiety in synthetic/medicinal chemistry, we report here the first example of efficient synthesis of 2-pyrazolines with a CF₃- and alkyne-substituted quaternary carbon center. This methodology has the advantages of high functional group compatibility, the avoidance of base and open-flask conditions, easily available and easy to handle reagent, and broad substrate scope. Notably, this protocol allows for the late-stage functionalization of biologically active molecules and the gram-scale synthesis.

Highly Stereoselective Synthesis of Tetrasubstituted Vinyl Selenides via Rhodium-Catalyzed [1,4]-Acyl Migration of Selenoesters and Diazo Compounds

Herein, we disclose a highly stereoselective Rh(II)-catalyzed 1,4-acyl rearrangement of selenium esters and α-diazo carbonyl compounds, which provides an efficient method for synthesizing tetrasubstituted vinyl selenides. Furthermore, this reaction also offers a synthetic tool for medium and large ring compounds.

Asymmetric Addition of α-Diazomethylphosphonate to Alkylideneindolenine Catalyzed by a Trifunctional BINAP-Based Monophosphonium Salt

A series of trifunctional BINAP-based monophosphonium phase-transfer catalysts were developed and used in the asymmetric addition of α-diazomethylphosphonates to vinylogous imines formed in situ from sulfonylindoles. This methodology tolerates a broad scope of 2-unsubstituted sulfonyl indoles, which have seldom achieved high enantioselectivities in similar asymmetric reactions with other nucleophiles. Chiral 3-sec-alkyl-substituted indoles containing α-diazophosphonate were afforded in up to 99% yield and 95% ee.

Recent Advances in the Transition Metal-Free Synthesis of Heterocycles from α, β-Unsaturated Ketones

Heterocyclic compounds are an inevitable part of our life. These important classes of molecules have a wide range of applications starting from life-sustaining drugs to agrochemicals. Numerous methods, including metal...

Phosphorus-Based Catalysis

Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.

Synthesis of heterocyclic compounds through nucleophilic phosphine catalysis

Nucleophilic phosphine catalysis is a practical and powerful tool for the synthesis of various heterocyclic compounds with the advantages of environmentally friendly, metal-free, and mild reaction conditions. The present report summarizes the construction of four to eight-membered heterocyclic compounds containing nitrogen, oxygen and sulphur atoms through phosphine-catalyzed intramolecular annulations and intermolecular [2+2], [3+2], [4+1], [3+1+1], [5+1], [4+2], [2+2+2], [3+3], [4+3] and [3+2+3] annulations of electron-deficient alkenes, allenes, alkynes and Morita-Baylis-Hillman carbonates.

Phosphine-catalyzed conjugate cyanation of β-trifluoromethyl enones: access to α-trifluoromethyl γ-carbonyl nitriles

Herein, we developed an efficient conjugate cyanation of β-trifluoromethyl enones with TMSCN mediated by phosphine and methyl acrylate.

Iodine-Catalyzed Regioselective Oxidative Cyclization of Aldehyde Hydrazones with Electron-Deficient Olefins for the Synthesis of Mefenpyr-Diethyl

A regioselective synthesis of polysubstituted dihydropyrazoles and pyrazoles through an iodine-catalyzed oxidative cyclization strategy of aldehyde hydrazones with electron-deficient olefins is described. The protocol adopts very mild reaction conditions and provides desirable yields. The reaction is supposed to proceed via a cascade C-H functionalization, C-N bond formation, and oxidation sequential processes. The overall simplicity and regioselectivity of the catalytic system make this approach a valuable and step-economical tool to construct a C-C bond for the synthesis of Mefenpyr-Diethyl.

Mechanisms of phosphine-catalyzed [3+3] cycloaddition of ynones and azomethine imines: a DFT study

Mechanisms of PPh₃-catalyzed [3+3] cycloaddition between a ynone and an azomethine imine.

Insights into the mechanisms of Ag-catalyzed synthesis of CF3-substituted heterocycles via [3+2]-cycloaddition from α-trifluoromethylated methyl isocyanides: effects of DBU and exploration of diastereoselectivity

The diastereoselectivity of [3+2]-cycloaddition can be reasonably explained by the analysis of steric hindrance using DFT calculations.