Iron/TEMPO-catalyzed direct aerobic oxidative coupling of methyl-mubstituted N-heteroazaarenes with alcohols

Solid acids as cocatalysts in the chelation-assisted hydroacylation of alkenes and alkynes

The use of homogeneous Brønsted acid cocatalysts (such as benzoic acid) in hydroacylation reactions via imine intermediates has been extensively studied. However, the use of heterogeneous cocatalysts has been limited to montmorillonite K10. Thus, we can use other solid acids to increase the efficiency of the reaction. In this study, we describe the effects of sulfated zirconia, Al-MCM-41 or superacid modified montmorillonite on the hydroacylation of alkenes and alkynes with aldehydes via imine intermediates and in the presence of the Wilkinson complex. Furthermore, we addressed the dual role of montmorillonite, a redox reagent in the presence of TEMPO and an acid solid, allowing the direct use of benzyl alcohols as substrates to generate saturated or α,β-unsaturated ketones.

Efficient synthesis of amides from secondary alcohols and CH3CN promoted by Fe(NO3)3·9H2O

The Ritter reaction is the most attractive method for synthesizing amides, and various acids have been used to promote this reaction. Compared to these acids, Fe(NO3)3·9H2O is less toxic and costly, and it shows relatively high Lewis acidity and great catalytic activity. In this study, a simple and efficient protocol involving Fe(NO3)3·9H2O as an additive for the synthesis of amides was developed. Various secondary alcohols could be reacted with CH3CN to obtain their corresponding products, with CH3CN being used as a reactant and solvent. This protocol was found to be applicable to a wide range of alcohols and nitrile substrates. In general, it was found that substrates containing electron-donating-groups offered the corresponding amides in good to excellent yields, while those with electron-withdrawing groups offered low to moderate yields. Meanwhile, this approach was scalable to the gram level, offering an attractive opportunity for further application in organic synthesis.

Harnessing alcohols as sustainable reagents for late-stage functionalisation: synthesis of drugs and bio-inspired compounds

Alcohol is ubiquitous with unparalleled structural diversity and thus has wide applications as a native functional group in organic synthesis. It is highly prevalent among biomolecules and offers promising opportunities for the development of chemical libraries. Over the last decade, alcohol has been extensively used as an environmentally friendly chemical for numerous organic transformations. In this review, we collectively discuss the utilisation of alcohol from 2015 to 2023 in various organic transformations and their application toward intermediates of drugs, drug derivatives and natural product-like molecules. Notable features discussed are as follows: (i) sustainable approaches for C-X alkylation (X = C, N, or O) including O-phosphorylation of alcohols, (ii) newer strategies using methanol as a methylating reagent, (iii) allylation of alkenes and alkynes including allylic trifluoromethylations, (iv) alkenylation of N-heterocycles, ketones, sulfones, and ylides towards the synthesis of drug-like molecules, (v) cyclisation and annulation to pharmaceutically active molecules, and (vi) coupling of alcohols with aryl halides or triflates, aryl cyanide and olefins to access drug-like molecules. We summarise the synthesis of over 100 drugs via several approaches, where alcohol was used as one of the potential coupling partners. Additionally, a library of molecules consisting over 60 fatty acids or steroid motifs is documented for late-stage functionalisation including the challenges and opportunities for harnessing alcohols as renewable resources.

Organocatalytic Asymmetric Vinylogous Michael Addition of Electron-Deficient Aryl Alkane Nucleophiles to Enals

We report herein a protocol for an organocatalyzed asymmetric vinylogous Michael addition of aryl alkane nucleophiles with enals under base- and additive-free conditions. A series of allylic building blocks were obtained in 60%-93% yield and 88-99% ee with 20 mol % diphenylprolinol silyl ether as catalyst. This protocol has advantages such as excellent chemoselectivity and regioselectivity, good tolerance of functionalities, and simple reaction conditions.

Selective Iron Catalyzed Synthesis of N-Alkylated Indolines and Indoles

Whereas iron catalysts usually promote catalyzed C3-alkylation of indole derivatives via a borrowing-hydrogen methodology using alcohols as the electrophilic partners, this contribution shows how to switch the selectivity towards N-alkylation. Thus, starting from indoline derivatives, N-alkylation was efficiently performed using a tricarbonyl(cyclopentadienone) iron complex as the catalyst in trifluoroethanol in the presence of alcohols leading to the corresponding N-alkylated indoline derivatives in 31-99 % yields (28 examples). The one-pot, two-step strategy for the selective N-alkylation of indolines is completed by an oxidation to give the corresponding N-alkylated indoles in 31-90 % yields (15 examples). This unprecedented oxidation methodology involves an iron salt catalyst associated with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and a stoichiometric amount of t-BuOOH at room temperature.

Excellent Eco-friendly Selective Alcohols Oxidation by an Acid Functionalized Imidazolium Based Ionic Liquid

Aims:

A green route for the oxidation of alcohols to corresponding carbonyl compounds in room temperature ionic liquid ([CEMIM]BH4) was developed by using hydrogen peroxide as the oxygen source. In aqueous solution at room temperature, 0.2 mol% of ([CEMIM]BH4) showed excellent catalytic properties for selective oxidation of aromatic and aliphatic alcohols

Background:

One of the vital reactions in organic synthesis is the oxidation of alcohols to carbonyl compounds. In particular, the conversion of primary alcohols to aldehydes has received a variety of applications as they are used as intermediates in fine chemicals mostly for the perfume industry.

Objective:

In the present work, we have reported an effective green route for the selective oxidation of alcohols to the carbonyl compounds using peroxide in an ionic liquid 1-carboxyethyl-3-methyl-imidazolium tetrahydroborate ([CEMIM]BH4)

Methods::

A mixture of alcohol (2 mmol), ([CEMIM]BH4) (0.2 mol%), H2O2 (2 mmol) were stirred thoroughly with the help of a magnetic stirrer for 10 min at ambient temperature

Results:

The catalytic activity of ([CEMIM]BH4) is very effective, which reflects its good solvating nature during the oxidation.

Conclusion:

In conclusion, the series of experiments described represents a useful method for the oxidation of primary and secondary alcohols to carbonyl compounds at room temperature. The catalyst can be easily prepared and is therefore extremely cost-effective. The rapid reaction times for the substrates mean a large number of materials may be screened in parallel over a short period of time.

Recent advances on non-precious metal-catalyzed C-H functionalization of N-heteroarenes

N-Heteroarenes are widely used for numerous medicinal applications, lifesaving drugs and show utmost importance as intermediates in chemical synthesis. This feature article highlights the recent advances, from 2015 to August 2021, on sp² and sp³ C-H bond functionalization reactions of various N-heteroarenes catalyzed by non-precious transition metals (Mn, Co, Fe, Ni, etc.). The salient features of the report are: (i) the development of newer catalysis for Csp²-H activation of N-heteroarenes and categorized into alkylation, alkenylation, borylation, cyanation, and annulation reactions, (ii) recent advances on Csp³-H bond functionalization of N-heteroarenes considering newer approaches for alkylation as well as alkenylation processes, and (iii) synthetic applications and practical utility of the catalytic protocols utilized for late-stage drug development; (iv) scope for the development of newer catalytic protocols along with mechanistic studies and detail mechanistic findings of various important processes.