Diastereoselective multicomponent synthesis of (4RS,6SR)-4,6-diaryl-5,5-dicyano-2-methyl-1,4,5,6-tetrahydropyridine-3-carboxylates

Catalyst-free inverse-electron-demand aza-Diels-Alder reaction of 4,4-dicyano-2-methylenebut-3-enoates and 1,3,5-triazinanes: access to polysubstituted tetrahydropyridines

An inverse-electron-demand aza-Diels-Alder reaction between 4,4-dicyano-2-methylenebut-3-enoates and 1,3,5-triazinanes under catalyst-free and additive-free conditions was developed, which provided a highly convenient and straightforward method to construct a series of polyfunctionalized tetrahydropyridines in high yields. This strategy features numerous advantages, including high efficiency, good functional group tolerance, broad substrate scope, and environmentally friendly conditions.

Piperidine Derivatives: Recent Advances in Synthesis and Pharmacological Applications

Piperidines are among the most important synthetic fragments for designing drugs and play a significant role in the pharmaceutical industry. Their derivatives are present in more than twenty classes of pharmaceuticals, as well as alkaloids. The current review summarizes recent scientific literature on intra- and intermolecular reactions leading to the formation of various piperidine derivatives: substituted piperidines, spiropiperidines, condensed piperidines, and piperidinones. Moreover, the pharmaceutical applications of synthetic and natural piperidines were covered, as well as the latest scientific advances in the discovery and biological evaluation of potential drugs containing piperidine moiety. This review is designed to help both novice researchers taking their first steps in this field and experienced scientists looking for suitable substrates for the synthesis of biologically active piperidines.

Tetrahydropyridines’ Stereoselective Formation, How Lockdown Assisted in the Identification of the Features of Its Mechanism

The multicomponent reaction of aldehydes, cyano-containing C-H acids, esters of 3-oxocarboxylic acid and ammonium acetate led to unexpected results. The boiling of starting materials in methanol for one to two hours resulted in the formation of polysubstituted 1,4,5,6-tetrahydropyridines with two or three stereogenic centers. During the 2020 lockdown, we obtained key intermediates of this six-step domino reaction. A number of fast and slow reactions occurred during the prolonged stirring of the reaction mass at rt. Sequence: 1. Knoevenagel condensation; 2. Michael addition; 3. Mannich reaction; 4. cyclization—fast reactions and cyclization of the product polysubstituted 2-hydroxypiperidine—was isolated after 40 min stirring at rt. Further monitoring proved the slow dehydration of 2-hydroxypiperidine to obtain 3,4,5,6-tetrahydropyridine after 7 days. Then, four-month isomerization occurred with 1,4,5,6-tetrahydropyridine formation. All reactions were stereoselective. Key intermediates and products structures were verified by X-ray diffraction analysis. Additionally, we specified conditions for the selective intermediates’ preparation.

One-pot five-component high diastereoselective synthesis of polysubstituted 2-piperidinones from aromatic aldehydes, nitriles, dialkyl malonates and ammonium acetate

A novel five-component diastereoselective synthesis of polysubstituted 2-piperidinones is reported. The Knoevenagel condensation-Michael addition-Mannich cascade of two equivalents of aromatic aldehydes, nitriles, dialkyl malonates and ammonium acetate or aqueous ammonia in alcohols provides convenient access to alkyl (3SR,4RS,6SR)-5,5-dicyano-2-oxo-4,6-diarylpiperidine-3-carboxylates with three stereocenters in 52-90% or dialkyl (2SR,3RS,4RS,5SR)-2,4-diaryl-3-cyano-6-oxopiperidine-3,5-dicarboxylates with four stereocenters in 38-88%. The formation of products was highly stereoselective, with only one diastereomer formed. Ammonium acetate or aqueous ammonia plays a role both as a catalyst and as a nitrogen source. 2,4,6-triaryl-3,3,5,5-tetracyanopiperidines were obtained as a side products in the reactions with nitro-substituted aldehydes or with ethyl and n-propyl cyanoacetates. A series of 14 2-piperidinones and piperidines was assessed for antimicrobial activity against a panel of five bacteria and two fungi; no significant activity was observed. Two side piperidines with nitro substituents in aromatic ring possess bacteriostatic action against S. aureus ATCC 43300 and A. baumannii ATCC 19606 at 32 ug/mL.