Novel Selectivity in Carbohydrate Reactions, IV: DABCO-Mediated Regioselective Primary Hydroxyl Protection of Carbohydrates

The versatility of DABCO as a reagent in organic synthesis: a review

DABCO (1,4-diazabicyclo[2.2.2]octane) has garnered a lot of interest for numerous organic transformations since it is a low-cost, environmentally friendly, reactive, manageable, non-toxic and basic organocatalyst with a high degree of selectivity. Moreover, DABCO functions as a nucleophile as well as a base in a variety of processes for the synthesis of a wide array of molecules, including carbocyclic and heterocyclic compounds. Protection and deprotection of functional groups and the formation of carbon-carbon bonds are also catalyzed by DABCO. The reagent also finds applications in the synthesis of functional groups like isothiocyanate, amide and ester. Application of DABCO in cycloaddition, coupling, aromatic nucleophilic substitution, ring-opening, oxidation and rearrangement reactions is also noteworthy. This is a state of the art review that has encompassed a variety of processes for the synthesis of organic frameworks using DABCO.

Regioselective Carbohydrate Oxidations: A Nuclear Magnetic Resonance (NMR) Study on Selectivity, Rate, and Side-Product Formation

Palladium/neocuproine catalyzed oxidation of glucosides shows an excellent selectivity for the C3-OH, but in mannosides and galactosides, unselective oxidation was initially observed. For further application in more-complex (oligo)saccharides, a better understanding of the reaction, in terms of selectivity and reactivity, is required. Therefore, a panel of different glycosides was synthesized, subjected to palladium/neocuproine catalyzed oxidation and subsequently analyzed by qNMR. Surprisingly, all studied glucosides, mannosides, galactosides, and xylosides show selective oxidation of the C3-OH. However, subsequent reaction of the resulting ketone moiety is the main culprit for side product formation. Measures are reported to suppress these side reactions. The observed differences in reaction rate, glucosides being the most rapidly oxidized, may be exploited for the selective oxidation of complex oligosaccharides.

Diazepinium perchlorate: a neutral catalyst for mild, solvent-free acetylation of carbohydrates and other substances

Diazepinium perchlorate-promoted acetylation of free as well as partially protected sugars, phenols, thiophenols, thiols, other alcohols and amines is described.

Acyl transfer reactions of carbohydrates, alcohols, phenols, thiols and thiophenols under green reaction conditions

Acyl transfer reactions of various carbohydrates, alcohols, phenols, thiols and thiophenols were achieved at room temperature in high yields and catalytic efficiency in the presence of methane sulfonic acid, a green organic acid, under solvent-free conditions over short time periods.

Concise synthesis of 5-methoxy-6-hydroxy-2-methylchromone-7-O- and 5-hydroxy-2-methylchromone-7-O-rutinosides. Investigation of their cytotoxic activities against several human tumor cell lines

The synthesis of two novel 2-methylchromone-7-O-rutinosides is reported, and the in vitro biological activities of these compounds and their synthetic precursors have been investigated on the basis of their cytotoxicity against several human tumor cell lines. The synthesis features early stage assembly of the acidic labile glycosidic bond between sugar and 2-methylchromone aglycon under phase transfer catalyzed glycosidation conditions, whereas all the other standard glycosylation conditions specific to a wide array of rutinosyl donors bearing different anomeric leaving groups (e.g., SPh, OC(NH)CCl(3), Br, OH groups) failed to furnish any detectable products.