Exploiting the Strained Ion-Pair Interactions of Sterically Hindered Pyridinium Salts Toward S2 Glycosylation of Glycosyl Trichloroacetimidates.

We demonstrate here that strained and sterically hindered protonated 2,4,6-tri--butylpyridinium (TTBPy) tetrafluoroborate, a crystalline, bench stable salt serves as a mild and efficient organocatalyst for the S2 type displacement of glycosyl trichloroacetimidates toward the stereoselective synthesis of both α- and β-glycosides. The strained ion-pair interactions between the sterically hindered pyridinium cation and the tetrafluoroborate anion infuse unusual reactivity to the ions resulting in the unique anion assisted activation of alcohol. This mild activation of alcohol facilitates the S2 type displacement of glycosyl αtrichloroacetimidates into β-glycosides in a highly diastereoselective manner.

Synthesis of chiral functional polyhydroxylated arenes via Mukaiyama aldol reaction from Perlin aldehydes.

Functionalized aryl polyhydroxylated compounds could be of great synthetic value for natural product synthesis. However, the synthesis of such compounds usually requires multi-step synthesis or the usage of sensitive reagents. We present here a practically simple route for the synthesis of such functionalized arylpolyols from glycal derived α,β-unsaturated 2,3-dideoxy aldehyde as well as α,β-saturated 2,3-dideoxy aldehyde (Perlin aldehydes) via Mukaiyama cross aldol condensation in the presence of silyl enol ether and TiCl It was observed that the nature of the electronic substitution of the silyl enol ether does not play any role in the yield of the desired products.

-[1-(-MeOPhenyl)vinyl]benzoate PMPVB as a recyclable auxiliary for C-O and C-S bond formation reactions under Brønsted acid catalysis.

A practically simple and useful method is reported for the synthesis of ethers and thioethers Brønsted acid-catalyzed activation of -[1-(-MeOphenyl)vinyl]benzoate (PMPVB) donors derived from alcohols. The mechanism of action is based on the remote activation of an active alkene followed by intramolecular 5- cyclization leading to a reactive intermediate that can react a substrate dependent S1 or S2 mechanism with alcohols and thiol nucleophiles providing facile access to ether and thioether functionalities, respectively.

Regio- and Stereoselective -Glycosylation of Indoles Using -[1-(-MeO-Phenyl)vinyl]benzoates (PMPVB) as Glycosyl Donors under Brønsted Acid Catalysis.

The alkene-based -[1-(-MeO-phenyl)vinyl]benzoates (PMPVB) donors that can be remotely activated under catalytic Brønsted acidic conditions have been utilized to synthesize the -linked indolyl glycosides in a regio- and stereoselective manner. The highly reactive glycosyl donors allow the usage of the poorly nucleophilic -Boc and -acetyl indole derivatives, leading to the indolyl glycosides in excellent yields and stereoselectivities. Also, conditions were developed for recycling the byproduct, which significantly improves the potential of these donors.

Glycosyl -[1-(-MeO-Phenyl)vinyl]benzoates (PMPVB) as Easily Accessible, Stable, and Reactive Glycosyl Donors for O-, S-, and C-Glycosylations under Brønsted Acid Catalysis.

Methods suitable for the synthesis of both O- and S-glycosylations are relatively rare because commonly used promoters like halonium sources or gold catalysts are incompatible with thiols as nucleophiles. Here, we present (-MeO)phenylvinylbenzoates (PMPVB) as easily accessible, stable, and reactive alkene-based glycosyl donors that can be activated with catalytic amounts of a Brønsted acid. This activation protocol not only allows us to synthesize -glycosides but also can successfully provide S- and C-linked glycosides.

Catalytic stereoselective synthesis of 2-deoxy α-glycosides using glycosyl -[1-(-MeOPhenyl)Vinyl]Benzoate (PMPVB) donors.

2-Deoxy glycosyl -[1-(-MeOPhenyl)Vinyl]Benzoates (PMPVB) have been presented as stable, reactive glycosyl donors for the synthesis of 2-deoxy α-glycosides. The donors react under Brønsted acid conditions to provide the 2-deoxy-α-glycosides with very high stereocontrol. The observed high stereoselectivities were discussed with respect to the relative free energy differences between the anomeric reactive intermediates.

TfO···H-O-H Interaction-Assisted Generation of a Silicon Cation from Allylsilanes: Access to Phenylallyl Ferrier Glycosides from Glycals.

We demonstrate here that the strained and bulky protonated 2,4,6-tri--butylpyridine (TTBPy) triflate salt serves as a mild and efficient organocatalyst for the diastereoselective -Ferrier glycosylation of various glycals. The importance of the role of the 1/2 HO molecule trapped in the catalyst has been disclosed. The mechanism of action involves unique anionic triflate and HO hydrogen-bond interactions that assist the activation of allylsilanes, providing unprecedented access to diastereoselective phenylallyl Ferrier glycosides.

Sterically Strained Brønsted Pair Catalysis by Bulky Pyridinium Salts: Direct Stereoselective Synthesis of 2-Deoxy and 2,6-Dideoxy-β-thioglycosides from Glycals.

A sterically strained ionic Brønsted pair complex obtained from a sterically bulky base 2,4,6-tri--butylpyridine and hydrochloric acid imbues unusual reactivity to the anionic chloride. The complete shielding of the cationic [N-H] by the bulky ortho--butyl groups weakens the possible hydrogen-bonding interactions with the chloride anion, and the [N-H]···Cl distance is unusually longer (3.10 Å).