Rh(III)-Catalyzed (4 + 1) Annulation of Pyrazol-3-ones with Alkynoates via Ortho-Alkenylation/Cyclization Cascade: Synthesis of Indazole-Fused Pyrazoles

Combinatorial synthesis of substituted pyrazolo-fused quinazolines by the Rh(III)-catalyzed [5 + 1] annulation of phenyl-1H-pyrazol-5-amine with alkynoates and alkynamides

A Rh(III)-catalyzed C-H activation/cyclization cascade was developed for the first divergent synthesis of pyrazolo[1,5-a]quinazolines through a [5 + 1] annulation reaction exclusively. The one-pot procedure is recognized for its broad substrate scope, functional group tolerance, and high atom economy. Mechanistic studies reveal the reaction pathway, addressing current limitations. Notably, this catalytic transition metal-assisted tandem annulation smoothly proceeds through the reaction of substituted phenyl-1H-pyrazol-5-amine with an alkyne ester or amide, where a one ring carbon is provided by the alkynoate building block. This transformation highlights the potential of transition metal-catalyzed methods for synthesizing diverse pyrazolo[1,5-a]quinazoline frameworks.

DFT Study on Mechanism of Ni-Al Bimetallic-Catalyzed C-H Cyclization to Construct Tricyclic Imidazoles: Roles of NHC Ligand and AlMe3

The mechanism of the Ni-Al bimetallic-catalyzed C-H cyclization to construct tricyclic imidazoles is investigated using density functional theory calculations. The calculation result shows that the reaction mechanism involves sequential steps of substrate coordination, ligand-to-ligand hydrogen transfer (LLHT), and C-C reductive elimination to produce the final product tricyclic imidazole. The LLHT step is calculated to be the rate-determining step. The oxidative addition of the benzimidazole C-H bond to the Ni center and the insertion of the alkene into the Ni-H bond occur concertedly in the LLHT step. The effects of N-heterocyclic carbene (NHC) ligands and AlMe3 on the reactivity and regioselectivity were also analyzed. These calculation results shed light on some ambiguous suggestions from experiments.

Rapid Synthesis of Benzimidazole-Fused Isoindoles by Rh(III)/Ru(II)-Catalyzed [4 + 1] Cascade C-H/N-H Annulation of 2-Arylbenzimidazoles with Alkynoates and Alkynamide

A Rh(III)-catalyzed [4 + 1] cyclization of 2-arylbenzimidazoles with alkynoates through C-H activation/ortho-alkenylation/intramolecular annulation cascade to obtain benzimidazole-fused isoindoles is reported. The reaction of the Rh catalyst and internal alkyne ester provides benzo[4,5]imidazo[2,1-a]isoindole acetate exclusively. Conversely, internal alkyne amide participates in the annulation process in the presence of a Ru catalyst to provide benzo[4,5]imidazo[2,1-a]isoindole acetamide. The alkyne acts as a C1 synthon and undergoes [4 + 1] cyclization rather than traditional [4 + 2] annulation.

A Novel Method for the Pre-Column Derivatization of Saccharides from Polygonatum cyrtonema Hua. by Integrating Lambert-Beer Law and Response Surface Methodology

Traditional Chinese medicine (TCM) safety and effectiveness can be ensured by establishing a suitable quality assessment system. This work aims to develop a pre-column derivatization HPLC method for Polygonatum cyrtonema Hua. quality control. In this study, 1-(4'-cyanophenyl)-3-methyl-5-pyrazolone (CPMP) was synthesized and reacted with monosaccharides derived from P. cyrtonema polysaccharides (PCPs), followed by HPLC separation. According to the Lambert-Beer law, CPMP has the highest molar extinction coefficient of all synthetic chemosensors. A satisfactory separation effect was obtained under a detection wavelength of 278 nm using a carbon-8 column and gradient elution over 14 min, with a flow rate of 1 mL per minute. Glucose (Glc), galactose (Gal), and mannose (Man) make up the majority of the monosaccharide components in PCPs, and their molar ratios are 1.73:0.58:1. The confirmed HPLC method has outstanding precision and accuracy, establishing a quality control method for PCPs. Additionally, the CPMP showed a visual improvement from colorless to orange after the detection of reducing sugars, allowing for further visual analysis.