Clara Uriel

One pot/two donors/one diol give one differentiated trisaccharide: powerful evidence for reciprocal donor–acceptor selectivity (RDAS)

Three component, one-pot reactions involving equimolar amounts of the acceptor diol and both armed and disarmed donors presented simultaneously, produce a single double-differential glycosidation product; this phenomenon provides evidence for Reciprocal Donor Acceptor Selectivity (RDAS).

Thioglycoside and trichloroacetimidate donors in regioselective glycosidations. Comparison with n-pentenyl glycosides

Thioglycoside and trichloacetimidate donors show the same regiopreferences as NPG analogs for selective glycosidation of an altroside diol, indicating that the selectivity may be general for donors. They also undergo one-pot, double-differential-glycosidations to give a single trisaccharide out of four possibilities.

Six- versus five-membered ring formation in radical cyclization of 1-vinyl-5-methyl-5-hexenyl radicals

Abstract Radical cyclization of 1-vinyl-5-methyl-5-hexenyl radicals (radical numbering) affords six-membered ring products prevailing over the isomeric five-membered ring compounds; the former are generated through two reaction pathways: 6- endo – trig ring closure and rearrangement of intermediate methylenecyclopentyl radicals obtained by 5- exo – trig cyclization.

Stereoselective synthesis of C-ketosides by Lewis acid-catalyzed C-glycosylation of alkynyl-ketoses

C-Ketosides are conveniently prepared in a stereoselective manner from alkynyl-ketoses by reaction with carbon nucleophiles in the presence of a Lewis acid.

Reaction of 1,2-orthoesters with HF-pyridine: a method for the preparation of partly unprotected glycosyl fluorides and their use in saccharide synthesis.

Glycosyl fluorides can be prepared in an efficient manner by treatment of pyranose- or furanose-derived 1,2-orthoesters, with hydrogen fluoride pyridine (HF-py). The method is compatible with the presence of a variety of protecting groups, including tert-butyldiphenyl silyl ethers, and can be applied to sugar derivatives with free hydroxyl groups, thus avoiding the need for the protection-deprotection steps.

Some aspects of selectivity in the reaction of glycosyl donors

Some advantages, disadvantages, and anomalies of various donors in glycosidations are discussed. By studying several two‐component donor/acceptor‐diol reactions, it is shown that regiopreferences are not very sensitive to the type of donor used. However, in competitive glycosidations within a given type of donor and between different types of donor, it is shown that regio‐ and chemoselectivities must be indexed to donor reactivity. * Dedicated to the memory of Professor Jacques van Boom.

Ready access to a branched Man5 oligosaccharide based on regioselective glycosylations of a mannose-tetraol with n-pentenyl orthoesters

A branched Man(5) oligosaccharide has been synthesized by sequential regioselective glycosylations on a mannose-tetraol with n-pentenyl orthoester glycosyl-donors promoted by NIS/BF(3)·Et(2)O, in CH(2)Cl(2). An extended n-pentenyl chain was incorporated into the tetraol acceptor to facilitate (a) the solubility of the starting tetraol in CH(2)Cl(2), and (b) future manipulations at the reducing end of the Man(5) oligosaccharide.

Ferrier-Nicholas pyranosidic cations: application to diversity-oriented synthesis

Abstract Pyranosidic allylic (Ferrier) cations that share dicobalt hexacarbonyl propargyl (Nicholas) stabilization at C-1, can be easily generated by treatment of hexacarbonyldicobalt alkynyl glycals with BF3·OEt2, and display a remarkable reactivity leading to a variety of products. The substituent at O-6 in these glycals plays a pivotal role in directing the outcome of the transformations. Accordingly, 6-O-benzyl or 6-O-allyl groups cause a series of transformations resulting in the stereoselective formation of oxepanes through a process that involves an initial hydride transfer step from the allyl or benzyl substituent to the Ferrier–Nicholas cation. On the contrary, 6-OH derivatives undergo an overall ring contraction to branched tetrahydrofuran derivatives. 6-O-Silyl derivatives, in the presence of heteroaryl nucleophiles, were transformed into C-3 branched bis-C-C-glycosides, containing two of such molecules.

Furanose-based templates in the chemoselective generation of molecular diversity

Highly functionalized 1-exo-alkylidene-2,3-anhydro-, and 1’-halo-1-exo-alkylidene-2,3-anhydro-furanoses, which are accessible from D-mannose in four or five steps, respectively, can be efficiently transformed in furanose based templates with up to four sites of molecular diversity, by way of a serie...