Reactivity of polyhydroxyalkyl-heterocycles towards Lewis acids

Lewis acid catalysis and Green oxidations: sequential tandem oxidation processes induced by Mn-hyperaccumulating plants

Among the phytotechnologies used for the reclamation of degraded mining sites, phytoextraction aims to diminish the concentration of polluting elements in contaminated soils. However, the biomass resulting from the phytoextraction processes (highly enriched in polluting elements) is too often considered as a problematic waste. The manganese-enriched biomass derived from native Mn-hyperaccumulating plants of New Caledonia was presented here as a valuable source of metallic elements of high interest in chemical catalysis. The preparation of the catalyst Eco-Mn1 and reagent Eco-Mn2 derived from Grevillea exul exul and Grevillea exul rubiginosa was investigated. Their unusual polymetallic compositions allowed to explore new reactivity of low oxidative state of manganese-Mn(II) for Eco-Mn1 and Mn(IV) for Eco-Mn2. Eco-Mn1 was used as a Lewis acid to catalyze the acetalization/elimination of aldehydes into enol ethers with high yields; a new green and stereoselective synthesis of (-)-isopulegol via the carbonyl-ene cyclization of (+)-citronellal was also performed with Eco-Mn1. Eco-Mn2 was used as a mild oxidative reagent and controlled the oxidation of aliphatic alcohols into aldehydes with quantitative yields. Oxidative cleavage was interestingly noticed when Eco-Mn2 was used in the presence of a polyol. Eco-Mn2 allowed direct oxidative iodination of ketones without using iodine, which is strongly discouraged by new environmental legislations. Finally, the combination of the properties in the Eco-Mn catalysts and reagents gave them an unprecedented potential to perform sequential tandem oxidation processes through new green syntheses of p-cymene from (-)-isopulegol and (+)-citronellal; and a new green synthesis of functionalized pyridines by in situ oxidation of 1,4-dihydropyridines.

The long underestimated carbonyl function of carbohydrates – an organocatalyzed shot into carbohydrate chemistry

Several novel and highly stereoselective C–C bond formation processes of unprotected carbohydrates are described.

SiO2-Supported CeCl3·7H2O−NaI Lewis Acid Promoter: Investigation into the Garcia Gonzalez Reaction in Solvent-Free Conditions⊥

The Knoevenagel condensation of aldose sugars with beta-dicarbonyl compounds produces furan derivatives having polyhydroxyalkylated alkyl side chains; this reaction is known as the Garcia Gonzalez reaction. Despite the fact that these polyhydroxyalkyl furans are interesting scaffolds for synthetic chemists to utilize in the synthesis of a variety of biologically interesting molecules, the reported approach suffers from harsh conditions. The development of a general and more efficient protocol is of considerable importance, and in this manuscript, we wish to explore the role of the NaI in enhancing the activity of CeCl3.7H2O as a useful water-tolerant Lewis acid promoter for the Garcia Gonzalez reaction. The procedure proceeds with good yields at 50 degrees C using our system supported on SiO2 in solvent-free conditions and represents a simple and convenient methodology for the preparation of densely functionalized molecules. Furthermore, the first qualitative results obtained on mechanistic investigation on the role of iodide on this our heterogeneous reaction may be of value for optimization of existing organic transformations and for the development of new ones.

Hetaryleneaminopolyols and hetarylenecarbopeptoids: a new type of glyco- and peptidomimetics. Syntheses and studies on solution conformation and dynamics

Ready access to a new class of oligomers has been demonstrated by the synthesis of hetaryleneaminopolyols and hetarylenecarbopeptoids using 3-hydroxymethyl-5-(4-amino-4-deoxy-d-arabinotetritol-1-yl)-2-methylfuran and 5-(4-amino-4-deoxy-d-arabinotetritol-1-yl)-2-methyl-3-furoic acid as novel scaffolds. The conformational behavior of peptidomimetics 22, 23, 25, 26, and 36 have been analyzed by NMR spectroscopy and extensive molecular dynamics simulations. MD simulations using the GB/SA continuum solvent model for water and the MM3 force field provide a population distribution of conformers which satisfactorily agrees with the experimental NMR data for the torsional degrees of freedom of the molecule.