N-Si Heterolysis by Chiral (BOX)Cu(OTf) Catalysts for the Synthesis of Indole and Carbazole Glycosides.

Chiral Cu(II) bisoxazolines have been shown to catalyze the coupling of acetyl-protected carbohydrates with N-silylated indoles to give the corresponding N-glycosides. Preliminary mechanistic experiments indicated that catalysis occurs through formation of a Cu-indolide complex with concomitant formation of TMS-OTf which together activate the sugar and deliver the indole nucleophile.

Borane- and Silylium-Catalyzed Difunctionalization of Carbohydrates: 3,6-Anhydrosugar Enabled 1,6-Site Selectivity.

A novel diastereoselective, Lewis acid catalyzed 1,6-difunctionalization of galactose and mannose derivatives has been developed in one pot, via sequential nucleophile additions. Our studies point to the formation of a 3,6-anhydrosugar intermediate as key to the 1,6-site-selectivity. Starting material-specific reactivity occurs when competitive ring-opening C-O cleavage is possible, owed to basicity and stereoelectronic stabilization differences.

Switching between -Pyrano-, -Furano-, and Anhydro--pyranoside Synthesis (X = C, N) under Lewis acid Catalyzed Conditions.

A variety of -glycosides can be obtained from the fluoroarylborane (B(CF)) or silylium (RSi) catalyzed functionalization of 1-MeO- and per-TMS-sugars with TMS-X reagents. A one-step functionalization with a change as simple as the addition order and/or Lewis acid and TMS-X enables one to afford chiral synthons that are common (-pyranosides), have few viable synthetic methods (-furanosides), or are virtually unknown (anhydro--pyranosides), which mechanistically arise from whether a direct substitution, isomerization/substitution, or substitution/isomerization occurs, respectively.

Surprisingly big linker-dependence of activity and selectivity in CO reduction by an iridium(i) pincer complex.

Here, we report the quantitative electroreduction of CO2 to CO by a PNP-pincer iridium(i) complex bearing amino linkers in DMF/water. The electrocatalytic properties greatly depend on the choice of linker within the ligand. The complex 3-N is far superior to the analogues with methylene and oxygen linkers, showing higher activity and better selectivity for CO2 over proton reduction.

Silylpalladium Cations Enable the Oxidative Addition of C(sp)-O Bonds.

The synthesis and characterization of the room-temperature and solution-stable silylpalladium cations (PCy)Pd-SiR(CF)B (SiR = SiMeEt, SiHEt) and (Xantphos)Pd-SiR(BAr) (SiR = SiMeEt, SiHEt; Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; BAr = (3,5-(CF)CH)B) are reported. Spectroscopic and ligand addition experiments suggest that silylpalladium complexes of the type (PCy)Pd-SiR are three-coordinate and T-shaped. Addition of dialkyl ethers to both the PCy and Xantphos-based silylpalladium cations resulted in the cleavage of C(sp)-O bonds and the generation of cationic Pd-alkyl complexes.