Advancement of the Cleavage Methods of Carbohydrate-derived Isopropylidene and Cyclohexylidene Ketals

Abstract:

Carbohydrates, amino acids, and nucleosides, the fundamental building blocks of complex biomolecules in nature, are essential starting materials for the fabrication of natural and unnatural structural entities, which necessitate the masking and demasking of various functional groups with the utmost chemoselectivity, mildness, and efficiency to avoid unintended bond breaking and formation, as well as associated reactions. Ketals, benzylidene, methoxymethyl, p-methoxybenzyl, silyl ethers, trityl, tert-butyl carbamate, and other functional groups are widely used in modern organic synthesis. In carbohydrate chemistry, the commonly used protecting functionality of isopropylidene and cyclohexylidene ketals necessitates effective methods for selective cleavage. This review summarises different methods for deblocking isopropylidene and cyclohexylidene ketals using inorganic acids, Lewis acid, silica-supported inorganic acids, Amberlite-120 (H+) resin, phosphotungstic acid, Nafion-H, NaBArF4.2H2O, montmorillonite clay, Dowex 50W-X8, camphorsulphonic acid (CSA), ceric ammonium nitrate, molecular iodine, ionic liquids, zeolites and so on.

Nascent-HBr-Catalyzed Removal of Orthogonal Protecting Groups in Aqueous Surfactants

Organic reactions in the aqueous environment have recently emerged as a promising research area. The generation of nascent-HBr from the slow hydrolysis of the dispersed catalyst, benzyl bromide, with the interior water present in the hydrophobic core of the confined micellar medium in aqueous surfactant is described for the first time. The sustained-release nascent-HBr enabled the chemoselective cleavages of acid-sensitive orthogonal functionalities present in carbohydrates, amino alcohols, and hydroxylated acyclic compounds in good to excellent yields.

1,4-Dithiothreitol mediated cleavage of the acetal and ketal type of diol protecting groups

An efficient deprotection of the ketal and acetal type protecting groups has been achieved with Brønsted acid as a catalyst and 1,4-dithiothreitol as a ketal or acetal exchange reagent.

Grindstone chemistry: protic ionic liquid-substrate tuned green synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity

An environmentally benign and highly substrate-protic ionic liquid controlled synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity is demonstrated through grinding a mixture of OPD, aldehydes and catalyst.

A protic ionic liquid catalyzed strategy for selective hydrolytic cleavage of tert-butyloxycarbonyl amine (N-Boc)

An efficient strategy for selective hydrolytic cleavage of N-tert-butyloxycarbonyl (Boc) group is devised using protic ionic liquid as catalyst. The cleavage reaction proceeded well in the presence of many other labile protecting groups.

General solvent-free ionic liquid catalyzed C–N/C–C coupled cyclization to diverse dihydropyrimidinones and new organic materials: Langmuir–Blodgett film study

An ionic liquid catalyzed dual C–N/C–C coupled cyclization under solvent-free green conditions to DHPMs and their innovative new organic materials by LB film study are demonstrated.

Phthalate tethered strategy: carbohydrate nitrile oxide cycloaddition to 12–15 member chiral macrocycles with alkenyl chain length controlled orientation of bridged isoxazolines

The highly selective synthesis of phthalate templated bridged sugar-based isoxazoline macrocyclic lactones is demonstrated through INOC with alkene.