Influence of Anion-Binding Schreiner’s Thiourea on DMAP Salts: Synergistic Catalysis toward the Stereoselective Dehydrative Glycosylation from 2-Deoxyhemiacetals

Abstract

Amines are used as additives to facilitate or increase the host−guest chemistry between the thiourea and the anions of Bronsted acids. However, we here demonstrate, for the first time, the synergistic effect of the combination of DMAP/HCl/ Schreiner's thiourea in catalyzing dehydrative glycosylation. The variations in the electronic effects of the cationic Bronsted acid part (the protonated DMAP) in the presence of chloride binding Schreiner's thiourea have been discussed using NMR and X-ray crystallographic techniques.

Thiourea-catalysed conjugate additions of amines to vinyl phosphonates and phosphinates

“…NMR analysis has previously been used to provide evidence for H-bonding interactions between thiourea catalysts and substrates. 59–61 We noted that the solubility of catalyst 1 in CDCl 3 was increased dramatically in the presence of diethyl vinylphosphonate which is consistent with formation of an H-bonded complex between the two species. H-Bonding interactions between thioureas and phosphoryl compounds have been studied using 31 P NMR and used to create a scale of catalyst H-bonding ability.…”

Reshuffle Bonds by Ball Milling: A Mechanochemical Protocol for Charge-Accelerated Aza-Claisen Rearrangements

“…N , N ′−Bis [3,5−bis(trifluoromethyl)phenyl]−thiourea (Schreiner’s thiourea catalyst). The title compound was prepared according to a modified literature procedure [ 139 ]. A 4 mL-GC vial was charged with 3,5-bis(trifluoromethyl)aniline (573 mg, 2.50 mmol, 1.00 equiv.)…”

Recent Advances in Stereoselective Chemical O-Glycosylation Reactions

“…Very recently Kancharala et al have reported the influence of anion-binding thiourea ( 12 ) on 4-dimethylaminopyridine salts toward α-selective synthesis of 2-deoxyglycosides ( 124 ) from their corresponding hemiacetals ( Ghosh et al, 2021 ). Combination of Schreiner’s thiourea ( 12 ), DMAP and HCl was used for dehydrative glycosylation of hemiacetals ( 130 ) in 1,2-dichloroethane solvent at 40°C (IV in Scheme 11 ).…”