Synthesis最新文献

An efficient and eco-friendly procedure was developed for the synthesis of N-aryl-2-((3-aryl-1,2,4-oxadiazol-5-yl)thio)acetamides from N-aryl-2-thiocyanatoacetamides and substituted N-hydroxybenzimidoyl chlorides that were prepared easily from the commercially available anilines and aryl aldehydes, respectively. The N-aryl-2-thiocyanatoacetamide acts as a dipolarophile while the nitrile oxide formed in situ from substituted N-hydroxybenzimidoyl chloride acts as the nucleophilic partner in a 1,3-dipolar cycloaddition reaction mediated by triethylamine base in ethanol medium. The procedure affords excellent yields of desired products containing electron-withdrawing and electron-donating groups on the aromatic rings, in short reaction time with ease of operation. The procedure for the synthesis of scaffolds that are potentially valuable for their biological properties also offers the possibility of scale-up to higher quantities.

This study aims to delineate the synthesis of eugenol derivatives, starting with hydroxyl group protection and then the subsequent oxidation stages. Initially, eugenol underwent conversion into acetyleugenol and benzyleugenol during the protection phase. Subsequently, a kinetic oxidation of acetyleugenol with KMnO₄ via GC-MS analysis resulted in the identification of four compounds. The kinetic investigation indicated the primary formation of diolacetyleugenol, succeeded by aldehyde eugenol, which further gets converted into its respective carboxylic acid. Additionally, acetyleugenol and benzyleugenol underwent oxidation with CrO₃, yielding the corresponding carboxylic acids.

The prominence of saturated N-heterocycle motifs in pharmaceuticals is undeniable. Challenges associated with the alkylation of saturated N-heterocycle scaffolds to efficiently access new drug analogues are hampered by synthetically laborious routes. Stereocontrolled alkyl-substitutions onto saturated N-heterocycles are particularly difficult to access in high yields by traditional synthetic methods. Alternatively, C–H bond functionalization provides a new and powerful synthetic avenue by directly and selectively functionalizing/alkylating/ arylating the abundantly available C–H bonds of saturated N-heterocycles. This review highlights complementary methods for directly activating and functionalizing C–H bonds of saturated N-heterocycles chemo-, regio-, and or stereoselectively to access alkylated products. This synthetic challenge has required catalyst development to access useful N-heterocyclic building blocks or for late-stage functionalization. Early transition metal, late transition metal, photoredox, and electrochemical methods are discussed. The selective functionalization of α, β, and γ C–H bonds to form new C–C, C–N, C–O, and C–B bonds is presented.

1 Introduction

2 Early Transition Metal Catalyzed α-Alkylation

3 Late Transition Metal Catalyzed α-Functionalization

4 Photoredox-Catalyzed α-Functionalization

5 Electrochemical α-Functionalization

6 C–H Functionalization of β and γ C–H Bonds

7 Conclusions/Outlook

The Minisci reaction, which has been around for more than five decades, is still the preferred tool for the straightforward alkylation of basic heteroarenes. The recent developments in photocatalysis have opened novel pathways for radical generation under milder and more sustainable conditions. Implementing this approach into the Minisci reaction has renewed interest in this transformation, which is attractive per se in Medicinal Chemistry. Aspects such as sacrificial oxidants, catalysts, and specific reaction conditions should be carefully examined to evaluate the practicability of the protocol. This short review focuses on recent advances (2020 to February 2024) in photoinduced Minisci-type reactions, emphasizing sustainability.

1 Introduction

2 Using Noble-Metal-Based Photocatalysts

3 Noble-Metal-Free Methods Using Sacrificial Oxidants

4 Noble-Metal-Free Methods Without Sacrificial Oxidants

5 Conclusions and Perspectives

The magnesium-mediated addition of bromoform to conjugated electron-deficient alkenes and imines, such as para-quinone methides (p-QMs) and aurone-derived azadienes, respectively, is reported here for the first time. While p-QMs undergo exclusive and hitherto unreported 1,6-addition of bromoform to afford benzylic tribromomethylated diarylmethanes, aurone-derived azadienes undergo both 1,2- and 1,4-additions to furnish α- and γ-tribromomethylamines. A mechanism involving the intermediacy of the tribromomethyl radical has been proposed based on control experiments and EPR studies. Representative synthetic transformations have also been carried out.

Spiro-heterocycles have attracted significant interest due to their unique biological properties with fewer side effects compared to traditional drugs. Herein, a novel method is reported for the synthesis of a series of spiro-heterocycles possessing a quinoline motif. The strategy utilizes rhodanine derivatives, hydrazonoyl chlorides, and 2-chloroquinoline-3-carbaldehyde, and proceeds via a one-pot sequential pseudo-five-component reaction. The reactions are found to proceed in a regioselective and chemoselective manner.

Starting from an l-serine-derived multifunctional aminobutenolide as a common chiral building block, stereoselective synthetic routes to representative examples of di-, tri-, and tetrahydroxylated iminosugars have been developed. Key steps in the synthetic routes involved an intramolecular aminolysis protocol to form the azaheterocyclic core, and functionalization of a resident alkene moiety towards installation of the desired substituents at the various positions of the piperidine ring. The strategy and the approach described are expected to provide flexible synthetic routes to various iminosugar scaffolds of structural and medicinal chemical significance.