Nucleophilic substitution reactions of C-4 sulfur-substituted tetrahydropyran acetals revealed that neighboring-group participation does not control product formation. Spectroscopic evidence for the formation of an intermediate sulfonium ion is provided, as are data from nucleophilic substitution reactions demonstrating that products are formed from oxocarbenium ion intermediates. The selectivity was not sensitive to solvent or to which Lewis acid was employed. The identity of the heteroatom at the C-4 position also did not significantly impact diastereoselectivity. Consequently, neighboring-group participation was not responsible for the formation of either the major or the minor products. These studies implicate a Curtin-Hammett kinetic scenario in which the formation of a low-energy intermediate does not necessitate its involvement in the product-forming pathway.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1021/ja0767783 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Mechanism of C-3 Acyl Neighboring Group Participation in Mannuronic Acid Glycosyl Donors.
J Am Chem Soc
January 2025
Department of Synthetic Organic Chemistry, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, Nijmegen 6525 AJ, The Netherlands.
One of the main challenges in oligosaccharide synthesis is the stereoselective introduction of the glycosidic bond. In order to understand and control glycosylation reactions, thorough mechanistic studies are required. Reaction intermediates found by NMR spectroscopy often cannot explain the glycosylation's stereochemical outcome.
View Article and Find Full Text PDFCooperative Catalysis in Stereoselective - and -Glycosylations with Glycosyl Trichloroacetimidates Mediated by Singly Protonated Phenanthrolinium Salt and Trichloroacetamide.
J Am Chem Soc
December 2024
Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States.
The development of small-molecule catalysts that can effectively activate both reacting partners simultaneously represents a pivotal pursuit in advancing the field of stereoselective glycosylation reactions. We report herein the development of the singly protonated form of readily available phenanthroline as an effective cooperative catalyst that facilitates the coupling of a wide variety of aliphatic alcohols, phenols, and aromatic amines with α-glycosyl trichloroacetimidate donors. The glycosylation reaction likely proceeds via an S2-like mechanism, generating β-selective glycoside products.
View Article and Find Full Text PDFSynthesis of a multivalent α-1,2-mannobiose ligand for targeting C-type lectins.
RSC Adv
November 2024
Department of Chemistry, Davidson College Davidson NC 28035 USA
The importance of lectins in biological processes such as pathogen recognition, cell adhesion, and cell recognition is well documented. C-Type lectins, which require calcium for binding, play an important role in the innate immune response by engaging carbohydrates presented as part of the human and pathogen glycocalyx. For example, lectins such as MBL, Dectin-2, langerin and DC-SIGN selectively recognize mannose rich (high-mannose) structures presented as part of the glycocalyx.
View Article and Find Full Text PDFHarnessing Free Sulfate Groups in Glycosylation Reactions.
Angew Chem Int Ed Engl
November 2024
Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, 560-0043, Toyonaka, Osaka, Japan.
General strategies for synthesizing sulfated oligosaccharides employ the protection of sulfate groups for glycosylation or post-sulfation after the synthesis of oligosaccharides. However, the chemical behavior of free sulfate groups in glycosylation reactions has not been thoroughly studied. We examined several glycosyl donors with free sulfate groups, but neither glycosyl imidates nor thioglycosides achieved products.
View Article and Find Full Text PDFAcetal Substitution Reactions: Stereoelectronic Effects, Conformational Analysis, Reactivity vs. Selectivity, and Neighboring-Group Participation.
Synlett
September 2024
Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003 USA.
Acetal substitution reactions can proceed by a number of mechanisms, but oxocarbenium ion intermediates are involved in many of these reactions. Our research has focused on understanding the conformational preferences, structures, and reactions of these intermediates. This Account summarizes our observations that electrostatic effects play a significant role in defining the preferred conformations, and that torsional effects determine how those intermediates react.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!