Optically PureN-Hydroxy-O-triisopropylsilyl-α-l-amino Acid Methyl Esters from AlCl3-Assisted Ring Opening of Chiral Oxaziridines by Nitrogen Containing Nucleophiles

Total Synthesis of Pseudouridimycin

Pseudouridimycin (1), a potent antibiotic against both Gram-positive and Gram-negative bacteria including multi-drug-resistant strains with a new mode of action isolated from Streptomyces sp., was synthesized by a convergent strategy from 5'-amino-pseudouridine 5 and N-hydroxy-dipeptide 26 in 23% total yield. The key intermediate 26 was synthesized by hydroxylaminolysis of the nitrone derived from glutamine and subsequent glycylation with glycine chloride. The synthetic method provides an efficient and practical way for the synthesis of N-hydroxylated peptidyl nucleoside.

WO3/Buckypaper Membranes for Advanced Oxidation Processes

Photocatalytic materials, such as WO₃, TiO₂, and ZnO nanoparticles, are commonly linked onto porous polymer membranes for wastewater treatment, fouling mitigation and permeation enhancement. Buckypapers (BPs) are entanglements of carbon nanotubes, which have been recently proposed as innovative filtration systems thanks to their mechanical, electronic, and thermal properties. In this work, flexible membranes of single wall carbon nanotubes are prepared and characterized as efficient substrates to deposit by chemical vapor deposition thin layers of WO₃ and obtain, in such a way, WO₃/BP composite membranes for application in advanced oxidation processes. The photocatalytic efficiency of WO₃/BP composite membranes is tested against model pollutants in a small continuous flow reactor and compared with the performance of an equivalent homogeneous WO₃-based reactor.

Recent Advances in the Catalytic Asymmetric Reactions of Oxaziridines

Oxaziridines have emerged as powerful and elegant oxygen- and nitrogen-transfer agents for a broad array of nucleophiles, due to the remarkably high and tunable reactivities. However, the asymmetric catalysis involving oxaziridines is still in its infancy. Herein, this review aims to examine recent advances in the catalytic asymmetric transformations of oxaziridines, including oxidation, amination, cycloaddition and deracemization.

Alternative formation of amides and β-enaminones from aroyl chlorides using the TiCl4-trialkylamine reagent system

Synthesis of amides and β-enaminones by the reaction of aroyl chlorides with the TiCl₄–NR₃reagent system.

Sustainable Synthesis of Oximes, Hydrazones, and Thiosemicarbazones under Mild Organocatalyzed Reaction Conditions

Pyrrolidine catalyzes very efficiently, presumably via iminium activation, the formation of acyloximes, acylhydrazones, and thiosemicarbazones derived from aromatic and aliphatic aldehydes using equimolar amounts of reagents and green solvents. Experimental simplicity and excellent yields after a simple filtration are the main advantages of the method, being an alternative to those currently available especially for the acyl derivatives, which do not work under uncatalyzed conditions. Its application to the synthesis of acyloximes by direct condensation between aldehydes and acylhydroxylamines is unprecedented.

Mechanistic Aspects of the Formation of Aldehydes and Nitriles in Photosensitized Reactions of Aldoxime Ethers

The photooxidation of a series of aldoxime ethers was studied by laser flash photolysis and steady-state (product studies) methods. Nanosecond laser flash photolysis studies have shown that chloranil (CA)-sensitized reactions of the O-methyl (1), O-ethyl (2), O-benzyl (3), and O-tert-butyl (4) benzaldehyde oximes result in the formation of the corresponding radical cations. In polar non-nucleophilic solvents such as acetonitrile, there are several follow-up pathways available depending on the structure of the aldoxime ether and the energetics of the reaction pathway. When the free energy of electron transfer (DeltaGET) becomes endothermic, syn-anti isomerization is the dominant pathway. This isomerization pathway is a result of triplet energy transfer from CA to the aldoxime ether. For substrates with alpha-protons (aldoxime ethers 1-3), the follow-up reactions involve deprotonation at the alpha-position followed by beta-scission to form the benziminyl radical (and an aldehyde). The benziminyl radical reacts to give benzaldehyde, the major product under these conditions. A small amount of benzonitrile is also observed. In the absence of alpha-hydrogens (aldoxime ether 4), the major product is benzonitrile, which is thought to occur via reaction of the excited (triplet) sensitizer with the aldoxime ether. Abstraction of the iminyl hydrogen yields an imidoyl radical, which undergoes a beta-scission to yield benzonitrile. An alternative pathway involving electron transfer followed by removal of the iminyl proton was not deemed viable based on charge densities obtained from DFT (B3LYP/6-31G*) calculations. Similarly, a rearrangement pathway involving an intramolecular hydrogen atom transfer process was ruled out through experiments with a deuterium-labeled benzaldehyde oxime ether. Studies involving nucleophilic solvents have shown that all aldoxime ethers reacted with MeOH by clean second-order kinetics with rate constants of 0.7 to 1.2 x 10(7) M(-1) s(-1), which suggests that there is only a small steric effect in these reactions. The steady-state experiments demonstrated that under these conditions no nitrile is formed. This is explained by a mechanistic scheme involving nucleophilic attack on the nitrogen of the aldoxime ether radical cation, followed by solvent-assisted [1,3]-proton transfer and elimination of an alcohol, similar to the results obtained for a series of acetophenone oxime ethers.