Recent progress in the radical α-C(sp3)-H functionalization of ketones

Breast cancer cell targeting of L-leucine-PLGA conjugated hybrid solid lipid nanoparticles of betulin via L-amino acid transport system-1

The aim of fabricating hybrid solid lipid nanoparticles (HSLN) was to enhance the delivery of betulin to triple negative beast cancer cells through the intravenous route via L-amino transporter system-1, using L-leucine-PLGA conjugate (Conj-HSLN) by hot high pressure homogenization method. Betulin (BN), having potent anticancer and antioxidant activity, faces challenges due to poor water solubility and permeability, affecting its bioavailability. The results revealed Conj-HSLN with particle size 318.3 ± 0.25 nm. The percent cumulative BN release from Conj-HSLN was 57.763%, 24h. The cytotoxicity study in MB-MDA-231 cell depicts, LD50 67.73 µg/ml in Conj-HSLN. Pharmacokinetics study reveals enhanced Cmax and half-life in Conj-HSLN (32.12 ± 0.25 µg/ml, 4.72 ± 0.53 h) than raw BN (1.31 ± 0.21 µg/ml, 7.54 ± 0.34 h). Enhanced distribution at tumor site (11.5967% ID, 2h) in Conj-HSLN signifies the role of L-leucine in the transport system. Pharmacodynamic study shows mean tumor volume of 765.3 ± 85.884, and 1450.01 ± 219.361 mm3 in Conj-HSLN, and BN respectively at 3rd week of treatment. Standardized uptake value attributed reduced glucose uptake, due to inhibited tumor growth and proliferation, confirmed tumor biomarkers assay, VEGF and Caspase-9. In conclusion, the targeted controlled release L-leucine conjugated-BN loaded HSLN is stable, safe, and effective against triple negative breast cancers.

Mild Hydroalkylation of Terminal Olefins Via Decatungstate/Thiol Cooperative Photocatalysis

Here we report the use of a tetrabutylammonium decatungstate (TBADT)/thiol photocatalytic system for selective addition of acetone and other simple ketone, nitrile, and chlorocarbon functionalities to terminal olefins. This system avoids the use of energetic reagents such as peroxides and proceeds under mild conditions using Earth-abundant element catalysts, providing a sustainable approach to C-C bond formation using activated olefins. Initial exploration reveals that hydroalkylation of unactivated olefins is also possible, though in lower efficiency, and preliminary mechanistic experiments are consistent with a radical mechanism.

Mechanisms of C(sp3)-H Functionalization of Acetonitrile or Acetone with Alkynes: A DFT Investigation

The mechanisms for the C(sp3)-H activation and addition reactions between acetonitrile (or acetone) and alkynes have been investigated with the M06-2X-D3/ma-def2-TZVP method and basis set. The SMD (solvation model based on solute electron density) model was applied to simulate the solvent effect. In the first and second reactions, 2-phenylbut-3-yn-2-ol reacted with acetonitrile and acetone, respectively. First, the C(sp3)-H activations of acetonitrile and acetone could be achieved by PhCOO• and t-BuO• radicals. Then, addition reactions converted 2-phenylbut-3-yn-2-ol into final products P1 and P2. Gibbs free energy surfaces of these two reactions suggest that blue lines would be the favorable paths with lower Gibbs energy barriers, and the terminal C atom of the C≡C bond is the best reactive site. Moreover, the analysis of the IRI (Interaction Region Indicator) reveals the Z- and E-configuration transformations. While in the third and fourth reactions, methyl(2-(phenylethynyl)phenyl)sulfane has interactions with acetonitrile and acetone via some paths, respectively. Gibbs free energy profiles show that the C10 atom, rather than the C11 atom, has priority, and the blue lines are favorable. Furthermore, the action mode of Na2HPO4 could reduce the energy barrier and benefit the reaction. vdW (van der Waals) interactions play an important role in the choice for the reactive site. In the fifth (or sixth) reaction, it happened between 1-(2-(methylthio)phenyl)-3-phenylprop-2-yn-1-one and acetontrile (or acetone) to yield the final product P5 (or P6). The computational results uncovered the blue line is the best path, and the choice for the reactive site depends on the vdW interactions, which reveals the origin of selectivity. In addition, the investigation for the byproducts have been carried out, and these can explain the reason that only the main product is produced. Both of those can agree with the experimental results. The localized orbital locator (LOL) isosurfaces, Laplacian bond order (LBO), electron density of the bond critical point (ρBCP), electron spin density isosurface graphs, and IRI graphs can be used to analyze the structure and reveal the reaction substances.

Copper catalyzed C(sp3)-H/C(sp3)-H cross-coupling of arylacetic acid equivalents with methylarenes via α-carbonyl radicals

Arylacetic acid equivalents bearing a pyridine group undergo C(sp3)-H/C(sp3)-H cross coupling with diverse methylarenes in the presence of a copper based catalyst system. The reaction proceeds via the formation of α-carbonyl radicals giving access to α,β-diarylpropionic acids. Preliminary study suggests that the catalyst system is capable of transforming arylbenzyl ketones into 1,2,3-triaryl ketones.

Merging Photoinduced Electron Transfer with Hydrogen Atom Transfer: Formal β-C(sp3)-H Pyridination of Carbonyls

In this study, a novel approach that combines photoinduced electron transfer (ET) with hydrogen atom transfer (HAT) has been introduced for the selective β-C(sp3)-H pyridination of carbonyl compounds. This method is notable for its absence of transition metals and its ability to function under benign reaction conditions, resulting in a range of pyridinated carbonyl derivatives with consistently moderate to good yields. The significance of this technique is further underscored by its potential for the late-stage functionalization of pharmaceutically significant molecules. Mechanistic investigations confirmed that the reaction proceeds via a radical-mediated pathway.

Direct Synthesis of K-Region Functionalized Polycyclic Aromatic Hydrocarbons via Twofold Intramolecular C-H/C-H Arylation

Functionalized polycyclic aromatic hydrocarbons (PAHs) are essential building blocks for the bottom-up fabrication of structurally uniform nanocarbons. Herein we report a simple and efficient synthetic method toward K-region hydroxy-functionalized PAHs via TEMPO-mediated twofold intramolecular C-H/C-H arylations of 1-biphenyl-2-yl-2-aryl-ethanone derivatives. This method achieves high yields and selectivity, synthesizing a variety of PAH frameworks, including pyrenes, chrysenes, benzo[c]phenanthrenes, and benzo[k]tetraphenes. Our results also demonstrate the potential of these compounds as valuable candidates for the selective construction of larger PAH structures.

Methyl Ketones as Alkyl Halide Surrogates: A Deacylative Halogenation Approach for Strategic Functional Group Conversions

Alkyl halides are versatile precursors to access diverse functional groups (FGs). Due to their lability, the development of surrogates for alkyl halides is strategically important for complex molecule synthesis. Given the stability and ease of derivatization inherent in common alkyl ketones, here we report a deacylative halogenation approach to convert various methyl ketones to the corresponding alkyl chlorides, bromides, and iodides. The reaction is driven by forming an aromatic byproduct, i.e., 1,2,4-triazole, in which N'-methylpicolinohydrazonamide (MPHA) is employed to form a prearomatic intermediate and halogen atom-transfer (XAT) reagents are used to quench the alkyl radical intermediate. The reaction is efficient in yielding primary and secondary alkyl halides from a wide range of methyl ketones with broad FG tolerance. It also works for complex natural-product-derived and fluoro-containing substrates. In addition, one-pot conversions of methyl ketones to various other FGs and annulations with alkenes and alkynes through deacylative halogenation are realized. Moreover, an unusual iterative homologation of alkyl iodides is also demonstrated. Finally, mechanistic studies reveal an intriguing double XAT process for the deacylative iodination reaction, which could have implications beyond this work.

Photoredox-catalyzed 1,2-oxo-alkylation of vinyl arenes with 1,3-diketones: an approach to 1,4-dicarbonyls via C-C activation

A mild and inexpensive approach to synthesising a series of 1,4-diketones in moderate to excellent yields via 1,2-oxo alkylation has been developed using fluorescein as a photocatalyst and air as an oxidant. The key features include (i) varied substrate scope (39 examples); (ii) good functional group tolerance; (iii) unsymmetrical 1,4-dicarbonyls; (iv) late-stage functionalization of thymol and ibuprofen derivatives; and (v) the synthetic expansion to 5- and 6-membered N-, O- and S-containing heterocycles.

C-centered radical-initiated cyclization by directed C(sp3)–H oxidative functionalization

C(sp3)–H functionalization is attracting constant attention. This review emphasizes C-centered radicals initiated cyclization strategies by directed C(sp3)–H oxidative functionalization since 2012.

Di-tert-butyl peroxide as an effective two-carbon unit in oxidative radical cyclization toward 7-methylazolo[1,5-a]pyrimidines

An unexpected oxidative radical cyclization with DTBP as the C2 cyclic unit enables the assembly of privileged 7-methylazolo[1,5-a]pyrimidines.