132487-16-2Relevant articles and documents
Open-Close Strategy toward the Organocatalytic Generation of 2-Deoxyribosyl Oxocarbenium Ions: Pyrrolidine-Salt-Catalyzed Synthesis of 2-Deoxyribofuranosides
Ghosh, Titli,Mukherji, Ananya,Kancharla, Pavan K.
, p. 7488 - 7498 (2019)
The reaction of secondary amine salts with 2-deoxy-ribofuranoses under forcible conditions leads to the putative furanosyl oxocarbenium ion that is trapped with various alcohols to provide 2-deoxy-ribofuranosides. The observed anomeric selectivities range from an equimolar mixture to complete α-selectivity in the case of bulky sugar acceptors. Owing to the mechanism and temperature of the transformation, the generated oxocarbenium ion shows little or no facial preference towards the nucleophilic attack of non-carbohydrate acceptors and leads to a mixture of anomers in the case of benzyl and acetyl protected donors. However, the conformationally less flexible tetraisopropylsilyl protected donor reacted with both sugar and non-sugar acceptors in a stereoselective fashion. Besides, the glycosylation with 2-cyanoethanol gave the product with unexpected beta-selectivity presumably due to nitrile effect. The operationally simple organocatalytic protocol provides easy access to otherwise difficult 2-deoxy-ribofuranosides/disaccharides.
Highly Stereoselective Glycosylation Reactions of Furanoside Derivatives via Rhenium (V) Catalysis
Casali, Emanuele,Othman, Sirwan T.,Dezaye, Ahmed A.,Chiodi, Debora,Porta, Alessio,Zanoni, Giuseppe
, p. 7672 - 7686 (2021/06/21)
A novel approach for the formation of anomeric carbon-functionalized furanoside systems was accomplished through the employment of an oxo-rhenium catalyst. The transformation boasts a broad range of nucleophiles including allylsilanes, enol ethers, and aromatics in addition to sulfur, nitrogen, and hydride donors, able to react with an oxocarbenium ion intermediate derived from furanosidic structures. The excellent stereoselectivities observed followed the Woerpel model, ultimately providing 1,3-cis-1,4-trans systems. In the case of electron-rich aromatic nucleophiles, an equilibration occurs at the anomeric center with the selective formation of 1,3-trans-1,4-cis systems. This anomalous result was rationalized through density functional theory calculations. Different oxocarbenium ions such as those derived from dihydroisobenzofuran, pyrrolidine, and oxazolidine heterocycles can also be used as a substrate for the oxo-Re-mediated allylation reaction.
Secondary amine salt catalyzed controlled activation of 2-deoxy sugar lactols towards alpha-selective dehydrative glycosylation
Ghosh, Titli,Mukherji, Ananya,Srivastava, Hemant Kumar,Kancharla, Pavan K.
, p. 2870 - 2875 (2018/05/03)
A new organocatalytic glycosylation method exploiting the lactol functionality has been disclosed. The catalytic generation of glycosyl oxacarbenium ions from lactols under forcible conditions via weakly Br?nsted-acidic, readily available secondary amine salts affects the diastereoselective glycosylation of 2-deoxypyranoses and furanoses. This operationally simple iminium catalyzed activation of 2-deoxy hemi-acetals is a potential alternative to the existing cumbersome methods that need specialized handling. The mechanisms for this unique transformation and kinetic/thermodynamic effects have been discussed based on both experimental evidence and theoretical studies.
