Selective Cleavage of Methoxy Protecting Groups in Carbohydrates

Abstract

The selective cleavage of methoxy protecting groups next to hydroxy groups is achieved using a radical hydrogen abstraction reaction as the key step. Under the reaction conditions, the hydroxy group generates an alkoxyl radical that reacts with the sterically accessible adjacent methoxy group, which is transformed into an acetal. In the second step, the acetals are hydrolyzed to give alcohols or diols. A one-pot hydrogen abstraction-hydrolysis procedure was also developed. Good yields were usually achieved, and the mild conditions of this methodology were compatible with different functional groups and sensitive substrates such as carbohydrates.

Polyphosphates and Pyrophosphates of Hexopyranoses as Allosteric Effectors of Human Hemoglobin: Synthesis, Molecular Recognition, and Effect on Oxygen Release

“…[33d, 35,36] These characteristic features also apply for our derivatives, both protected phosphorylated (19,20,25,26) and sodium salts (31,32), as shown in Table 1.…”

“…Octabenzyl-1,2,3,4-(6-O-tert-butyldiphenylsilyl-a-d- , 1 H, H-3), 3.98-3.87 (m, 2 H, H-2, H-4), 3.80 (br d, J = 12.6, 1 H, H-6), 3.67 (dd, J = 12.8, 5.3, 1 H, H-6'), 3.54 (dd, J = 9.1, 4.8, 1 H, H-5); 13 À calcd for C 6 H 12 Na 3 O 18 P 4 : 564.8662, found: 564.8692. [32] Flash column chromatography (EtOAc ! 4 % CH 3 OH in EtOAc) as a white solid (77 %), ratio of a/b anomers 1/0.7: R f = 0.1 (EtOAc).…”

“…Reaction of parent sugars with TBDPS chloride was used to selectively block the primary hydroxy group at position 6. Whereas preparation of the silylated mannose derivative 15 has not been reported, those of glucose and galactose, 14 [31] and 16, [32] respectively, have been. However, we followed a modified procedure for the synthesis of all of them (Scheme 2).…”

Concise Access to the Skeleton of Protoilludane Sesquiterpenes through a Photochemical Reaction Cascade: Total Synthesis of Atlanticone C

“…Reported procedures for the ring opening of methylene acetals [25] require acidic conditions,w hich turned out to be not perfectly compatible with the substrate.F or example,t he yield of deprotection with trifluoroacetic acid anhydride and acetic acid in CH 2 Cl 2 [26] was only 36 %. Reported procedures for the ring opening of methylene acetals [25] require acidic conditions,w hich turned out to be not perfectly compatible with the substrate.F or example,t he yield of deprotection with trifluoroacetic acid anhydride and acetic acid in CH 2 Cl 2 [26] was only 36 %.…”

Selective methoxy ether cleavage of 2,6-dimethoxyphenol followed by a selective acylation

“…An extensive literature search revealed that various Lewis acids such as aluminum trihalides or boron trihalides have been used as ether-cleaving agents, 8–11 in particular AlCl 3 12 and BCl 3 13 can be used to selectively cleave aromatic methoxy groups adjacent to a carbonyl function without affecting other methoxy groups present in the molecule. Haraldsson et al have reported the selective cleavage of aromatic benzyl ethers with magnesium bromide via a neighboring group effect.…”