Accumulation, Characterization and Reactivity of Chiral Ammonium-Carboxonium Dications in Superacid.

The accumulation of chiral ammonium-oxocarbenium dications in superacid is evidenced by low-temperature NMR spectroscopy, X-ray diffraction analysis and confirmed by DFT calculations. Its potential for the diastereoselective remote hydrofunctionalization of non-activated alkene is also explored.

Evidence and exploitation of dicationic ammonium-nitrilium superelectrophiles: direct synthesis of unsaturated piperidinones.

Exploiting superacid activation, the reactivity of aminonitriles was enhanced through the transient formation of highly reactive ammonium-nitrilium superelectrophiles. Demonstrated by using in situ low-temperature NMR experiments and confirmed by X-ray diffraction analysis, these dications can be intramolecularly trapped by non-activated alkenes to generate unsaturated piperidinones, including enantioenriched ones, in a straightforward way.

Structural and Computational Analysis of 2-Halogeno-Glycosyl Cations in the Presence of a Superacid: An Expansive Platform.

An expansive NMR-based structural analysis of elusive glycosyl cations derived from natural and non-natural monosaccharides in superacids is disclosed. For the first time, it has been possible to explore the consequence of deoxygenation and halogen substitution at the C2 position in a series of 2-halogenoglucosyl, galactosyl, and mannosyl donors in the condensed phase. These cationic intermediates were characterized using low-temperature in situ NMR experiments supported by DFT calculations.

Defining the S1 Side of Glycosylation Reactions: Stereoselectivity of Glycopyranosyl Cations.

The broad application of well-defined synthetic oligosaccharides in glycobiology and glycobiotechnology is largely hampered by the lack of sufficient amounts of synthetic carbohydrate specimens. Insufficient knowledge of the glycosylation reaction mechanism thwarts the routine assembly of these materials. Glycosyl cations are key reactive intermediates in the glycosylation reaction, but their high reactivity and fleeting nature have precluded the determination of clear structure-reactivity-stereoselectivity principles for these species.

Evidence of Phosphonium-Carbenium Dication Formation in a Superacid: Precursor to Fluorinated Phosphine Oxides.

Unambiguously confirmed by low-temperature in situ NMR experiments, X-ray diffraction and vibrational spectroscopy, phosphonium-carbenium superelectrophiles are shown to be generated in strong acidic conditions. Representing crucial intermediates, their exploitation allows for the synthesis of unprecedented fluorinated (cyclic) phosphine oxides.