A Simple Iron-Catalyst for Alkenylation of Ketones Using Primary Alcohols

Iron-Catalyzed sp3 C-H Alkylation of Fluorene with Primary and Secondary Alcohols: A Borrowing Hydrogen Approach

The utilization of earth-abundant, cheap, and nontoxic transition metals in important catalytic transformations is essential for sustainable development, and iron has gained significant attention as the most abundant transition metal. A mixture of FeCl2 (3 mol %), phenanthroline (6 mol %), and KOtBu (0.4 eqivalent) was used as an effective catalyst for the sp3 C-H alkylation of fluorene using alcohol as a nonhazardous alkylating partner, and eco-friendly water was formed as the only byproduct. The substrate scope includes a wide range of substituted fluorenes and substituted benzyl alcohols. The reaction is equally effective with challenging secondary alcohols and unactivated aliphatic alcohols. Selective mono-C9-alkylation of fluorenes with alcohols yielded the corresponding products in good isolated yields. Various postfunctionalizations of C-9 alkylated fluorene products were performed to establish the practical utility of this catalytic alkylation. Control experiments suggested a homogeneous reaction path involving borrowing hydrogen mechanism with the formation and subsequent reduction of 9-alkylidene fluorene intermediate.

Iron- and base-catalyzed C(α)-alkylation and one-pot sequential alkylation-hydroxylation of oxindoles with secondary alcohols

The utilization of economical and environmentally benign transition metals in crucial catalytic processes is pivotal for sustainable advancement in synthetic organic chemistry. Iron, as the most abundant transition metal in the Earth's crust, has gained significant attention for this purpose. A combination of FeCl2 (5 mol%) in the presence of phenanthroline (10 mol%) and NaOtBu (1.5 equivalent) proved effective for the C(α)-alkylation of oxindole, employing challenging secondary alcohol as a non-hazardous alkylating agent. The C(α)-alkylation of oxindole was optimized in green solvent or under neat conditions. The substrate scope encompasses a broad array of substituted oxindoles with various secondary alcohols. Further post-functionalization of the C(α)-alkylated oxindole products demonstrated the practical utility of this catalytic alkylation. One-pot C-H hydroxylation of alkylated oxindoles yielded 3-alkyl-3-hydroxy-2-oxindoles using air as the most sustainable oxidant. Low E-factors (3.61 to 4.19) and good Eco-scale scores (74 to 76) of these sustainable catalytic protocols for the alkylation and one-pot sequential alkylation-hydroxylation of oxindoles demonstrated minimum waste generation. Plausible catalytic paths are proposed on the basis of past reports and control experiments, which suggested that a borrowing hydrogen pathway is involved in this alkylation.

Copper-catalyzed dehydrogenative cyclization/alkenylation towards dihydroquinolinones

An efficient copper-catalyzed one-pot sequential synthesis of alkenylated quinolinyl dihydroquinolinones is reported, utilizing ketones, 1,3-cyclohexanediones, and benzyl alcohols via dehydrogenative cyclization, followed by alkenylation. This highly straightforward method provides a mild and environmentally friendly approach, and scalable reactions are carried out without generating side products. Furthermore, a plausible reaction mechanism is proposed based on control-experiment studies and reaction monitoring via1H NMR analysis. In addition, the photophysical behavior of the synthesized products showed various responses in the absorption and emission spectra. Upon further examination, compound 4F was found to have acidochromic properties, leading to noticeable colour changes.

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.

Recent advances in cross-coupling of alcohols via borrowing hydrogen catalysis

Application of the borrowing hydrogen strategy facilitates utilization of abundantly available alcohols for linear or branched long-chain alcohols. Selective synthesis of such alcohols is highly challenging and involves the utilization of transition metal catalysts towards the desired cross-coupled product. Herein, we have highlighted recent advances (from 2015 to 2023) towards the synthesis of higher alcohols. Major focus has been given to the development of ligands, including transition metal catalysts. Judicious catalyst design plays a key role in the alkylation process and is summarised in this review.

Recent advances in the selective semi-hydrogenation of alkyne to (E)-olefins

Considering the potential importance and upsurge in demand, the selective semi-hydrogenation of alkynes to (E)-olefins has attracted significant interest. This article highlights the recent advances in newer technologies and important methodologies directed to (E)-olefins from alkynes developed from 2015 to 2023. Notable features summarised include the catalyst or ligand design and control of product selectivity based on precious and nonprecious metal catalysts for semi-hydrogenation to (E)-olefins. Mechanistic studies for various catalytic transformations, including synthetic application to bioactive compounds, are summarised.

Nickel-Catalyzed Chemodivergent Coupling of Alcohols: Efficient Routes to Access α,α-Disubstituted Ketones and α-Substituted Chalcones

Chemodivergent (de)hydrogenative coupling of primary and secondary alcohols is achieved utilizing an inexpensive nickel catalyst, (6-OH-bpy)NiCl2 . This protocol demonstrates the synthesis of branched carbonyl compounds, α,α-disubstituted ketones, and α-substituted chalcones via borrowing hydrogen strategy and acceptorless dehydrogenative coupling, respectively. A wide range of aryl-based secondary alcohols are coupled with various primary alcohols in this tandem dehydrogenation/hydrogenation reaction. The nickel catalyst, along with KOt Bu or K2 CO3 , governed the selectivity for the formation of branched saturated ketones or chalcones. A preliminary mechanistic investigation confirms the reversible dehydrogenation of alcohols to carbonyls via metal-ligand cooperation (MLC) and the involvement of radical intermediates during the reaction.

Structure-Activity Relationship Studies of Chalcones and Diarylpentanoids with Antitumor Activity: Potency and Selectivity Optimization

We previously reported that chalcone CM-M345 (1) and diarylpentanoid BP-C4 (2) induced p53-dependent growth inhibitory activity in human cancer cells. Herein, CM-M345 (1) and BP-C4 (2) analogues were designed and synthesized in order to obtain more potent and selective compounds. Compounds 16, 17, 19, 20, and 22-24 caused pronounced in vitro growth inhibitory activity in HCT116 cells (0.09 < GI50 < 3.10 μM). Chemical optimization of CM-M345 (1) led to the identification of compound 36 with increased selectivity for HCT116 cells expressing wild-type p53 compared to its p53-null isogenic derivative and low toxicity to non-tumor HFF-1 cells. The molecular modification of BP-C4 (2) resulted in the discovery of compound 16 with more pronounced antiproliferative activity and being selective for HCT116 cells with p53, as well as 17 with enhanced antiproliferative activity against HCT116 cells and low toxicity to non-tumor cells. Compound 16 behaved as an inhibitor of p53-MDM2 interaction, and compound 17 was shown to induce apoptosis, associated with an increase in cleaved PARP and decreased levels of the anti-apoptotic protein Bcl-2. In silico studies allowed us to predict the druglikeness and ADMET properties for 16 and 17. Docking and molecular dynamics studies predicted that 16 could bind stably to the MDM2 binding pocket.

Synthesis, odor characteristics and biological evaluation of N-substituted pyrrolyl chalcones

Base-mediated transition-metal free α-functionalization of N-substituted acetylpyrroles with commercial alcohols to generate various pyrrolyl chalcones is reported, and several prominent bioactive and flavor molecules were obtained.