“On water” cascade synthesis of benzopyranopyrazoles and their macrocycles

Recent Advances in the Synthesis of Pyrazole Derivatives

Pyrazole and its derivatives have gained wide attention in pharmaceutical, agrochemical and biological fields as well as in industry. They exhibit various biological activities such as anti-pyretic, anti-microbial, anti- inflammatory, anti-tumor, anti-viral, anti-histaminic, anti-convulsant, fungicidal, insecticidal, etc. In this review, we summarise the recent advances in the synthesis of pyrazole derivatives using various methodologies and covers literature from 2017-2020.

K2CO3-Catalyzed Rapid Conversion of N-Sulfonylhydrazones to Sulfinates

N-Sulfonylhydrazones derived from alkyl, aryl, and heteroaryl aldehydes and ketones undergo rapid conversion into the corresponding sulfinates when heated with 10 mol % K₂CO₃ in N,N'-dimethylethylene urea (DMEU) at elevated temperature. The reaction conditions are amenable to several functional groups and suitable for gram-scale synthesis. Under these base-catalyzed conditions, N-tosylhydrazones derived from O-allylated and O-propargylated 2-hydroxyarylaldehydes do not undergo the well-established intramolecular [3 + 2]-cycloaddition reactions and generate corresponding sulfinates in good yields. The base-catalyzed transformation proceeds via crucial rapid intermolecular protonation of the diazo intermediate 11 to generate diazonium ion 12, which upon nucleophilic displacement by the sulfonyl ion 10 provides the desired sulfinate selectively.

Greener Synthesis of Nitrogen-Containing Heterocycles in Water, PEG, and Bio-Based Solvents

The solvents used in chemistry are a fundamental element of the environmental performance of processes in corporate and academic laboratories. Their influence on costs, health safety, and nature cannot be neglected. Quantitatively, solvents are the most abundant constituents of chemical transformations; therefore, acting on solvents and replacing standard solvents with safer products can have a great ecological impact. However, not all green solvents are suitable for the wide scope of organic chemistry reactions. A second point to consider is that 50% of pharmaceutical drugs are nitrogen heterocycles compounds. It therefore appeared important to provide an overview of the more ecological methodologies for synthesizing this class of compounds. In this review, all publications since 2000 that describe green reactions leading to the formation of nitrogen heterocycles using safe solvents were considered. We chose water, PEG, and bio-based solvents for their negligible toxicity. The synthesis of five-, six-, and seven-membered aromatic nitrogen heterocycles using green reactions reported in the literature to date is described.

Regioselective Synthesis of Highly Functionalized Pyrazoles from N-Tosylhydrazones

A regioselective synthesis of highly functionalized pyrazoles from N-tosylhydrazones was developed. The reaction was general for a wide range of substrates and demonstrated excellent tolerance to a variety of substituents, and the method has been successfully applied to the formal synthesis of ibrutinib.