RESUMO
The synthesis of polycyclic aromatic compounds generally requires stoichiometric oxidants or homogeneous metal catalysts, however, the risk of contamination of inorganic residues can affect their properties. Here we present a microwave (MW)-assisted platinum on beaded activated carbon (Pt/CB)-catalyzed C-C bond formation of diarylacetylenes and aromatic hydrocarbons under continuous-flow conditions. Various fused aromatic compounds were continuously synthesized via dehydrogenative C(sp2)-C(sp2) and C(sp2)-C(sp3) bond formation with yields of up to 87% without the use of oxidants and bases. An activated, local reaction site on Pt/CB in the flow reaction channel reaching temperatures of more than three hundred degrees Celsius was generated in the catalyst cartridge by selective microwave absorption in CB with an absorption efficiency of > 90%. Mechanistic experiments of the transformation reaction indicated that a constant hydrogen gas supply was essential for activating Pt. This is an ideal reaction with minimal input energy and no waste production.
RESUMO
Glycosylation reactions of 5-thioglucopyranosyl trichloroacetimidates bearing ethereal protective groups at the 2-O-position 14-15, and 37 proceed smoothly to give alpha-glycosides stereoselectively by using a catalytic amount of silyl triflate. This methodology allowed us to achieve syntheses of sulfur-substituted isomaltotetraoside 2 and maltotetraoside 3. These studies also revealed that benzoyl-protected 5-thioglucopyranosyl trichloroacetimidate 12 underwent beta-selective glycosylation with C6-OH glucopyranosyl acceptors upon activation by BF3OEt2. This was applied for preparation of sulfur-substituted gentiobiosides 1 and 46.
Assuntos
Oligossacarídeos/química , Tioglucosídeos/química , Sequência de Carboidratos , Glicosilação , Espectroscopia de Ressonância Magnética , Dados de Sequência Molecular , Oligossacarídeos/síntese química , Espectrometria de Massas de Bombardeamento Rápido de Átomos , Tioglucosídeos/síntese químicaRESUMO
A general method for alpha-selective glycosylation with 5-thioglucopyranosyl donors followed by efficient deprotection of the resulting products was developed. This methodology was utilized in the synthesis of an isomaltotetraoside analogue.