Benzylic C-H Oxidation: Recent Advances and Applications in Heterocyclic Synthesis.

Benzylic C-H oxidation to form carbonyl compounds, such as ketones, is a fundamental transformation in organic synthesis as it allows for the preparation of versatile intermediates. In this review, we highlight the synthesis of aromatic ketones via catalytic, electrochemical, and photochemical oxidation of alkylarenes using different catalysts and oxidants in the past 5 years. Additionally, we also discuss the synthesis of heterocyclic molecules using benzylic C-H oxidation as a key step.

Synthesis of 2,4,5-Trisubstituted Oxazoles from Copper-Mediated Benzylic sp C-H Aerobic Oxidative Annulation of Ketones and Amines via a Cascade Reaction.

The functionalization of sp carbons is deemed challenging in synthetic organic chemistry yet has tremendous potential in producing potent organic compounds. A facile synthesis of 2,4,5-trisubstituted oxazoles through an oxidative, copper-catalyzed, and solvent-free annulation is described. Various arylated oxazoles were efficaciously synthesized at a mild temperature from readily available substrates under a molecular oxygen atmosphere.

Insights into structural and physicochemical properties required for β-hematin inhibition of privileged triarylimidazoles.

In this study, we investigated a series of triarylimidazoles, in an effort to elucidate critical SAR information pertaining to their anti-plasmodial and β-hematin inhibitory activity. Our results showed that in addition to the positional effects of ring substitution, subtle changes to lipophilicity and imidazole ionisability were important factors in SAR interpretation. Finally, adsorption analysis indicated that these compounds exert their effect by inhibiting β-hematin crystal growth at the fast growing 001 face.

An iodine/DMSO-catalyzed sequential one-pot approach to 2,4,5-trisubstituted-1-imidazoles from α-methylene ketones.

A sequential one-pot approach to 2,4,5-trisubstituted imidazoles has been developed from α-methylene ketones and aldehydes. This methodology employs air-moisture stable reaction conditions and an inexpensive iodine/DMSO system affording a diverse range of known and novel (substrate scope) 2,4,5-trisubstituted imidazoles in moderate to excellent yields. The iodine/DMSO system was extended to the domino convergent synthesis of two functionalized intermediates, benzil and benzaldehyde, to produce the final product.

The 'Ireland' one-pot alcohol oxidation coupling reactions: celebrating 30 years of diverse synthesis.

In 1985, Robert Ireland and co-worker were devising synthetic routes to polyether ionophore antibiotics and during this process several highly reactive aldehydes were encountered, which made their isolation and subsequent elaboration difficult. To circumvent this problem, the synthetic route commenced from the alcohol which was oxidized to the aldehyde and, to the crude mixture, was added the nucleophile. This procedure, dubbed the 'Ireland' oxidative process was found to be highly successful and adapted by many research groups the world over.

Convenient photooxidation of alcohols using dye sensitised semiconductors in combination with silver nitrate and TEMPO--an electron paramagnetic resonance study.

A mechanistic investigation into the photooxidation of alcohols using dye sensitised titanium dioxide and dye sensitised zinc oxide is described. The varying yields using the two photocatalysts have been explained using electron paramagnetic resonance (EPR) spectroscopy, which indicated that electron injection occurs in the dye sensitised ZnO system but is sluggish in the dye sensitised TiO(2) system. Due to the failure of the electron injection step, a 'break' in the photooxidative system occurs resulting in a decrease in the conversion of benzyl alcohol to benzaldehyde for the dye sensitised TiO(2) system.

Convenient photooxidation of alcohols using dye sensitised zinc oxide in combination with silver nitrate and TEMPO.

A novel photooxidative system using dye sensitised zinc oxide in combination with silver nitrate and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) in an aqueous solution is described. Under visible light irradiation the selective oxidation of alcohols to their corresponding aldehydes and ketones was effected in good to excellent yields.

Green oxidations: titanium dioxide induced tandem oxidation coupling reactions.

The application of titanium dioxide as an oxidant in tandem oxidation type processes is described. Under microwave irradiation, quinoxalines have been synthesized in good yields from the corresponding alpha-hydroxyketones.