Base-Free Iron Catalyzed Transfer Hydrogenation of Esters Using EtOH as Hydrogen Source.

Herein, we report on the use of the iron pincer complex Iron-MACHO-BH, in the base-free transfer hydrogenation of esters with EtOH as a hydrogen source. More than 20 substrates including aromatic and aliphatic esters and lactones were reduced affording the desired primary alcohols and diols with moderate to excellent isolated yields. It is also possible to reduce polyesters to the diols with this method, enabling a novel way of plastic recycling. Reduction of the renewable substrate methyl levulinate proceeds to form 1,4-pentanediol directly. The yields are largely governed by the equilibrium between the alcohol and the ethyl ester.

Selective Base-free Transfer Hydrogenation of α,ß-Unsaturated Carbonyl Compounds using iPrOH or EtOH as Hydrogen Source.

Commercially available Ru-MACHOTM -BH is an active catalyst for the hydrogenation of several functional groups and for the dehydrogenation of alcohols. Herein, we report on the new application of this catalyst to the base-free transfer hydrogenation of carbonyl compounds. Ru-MACHOTM -BH proved to be highly active and selective in this transformation, even with α,ß-unsaturated carbonyl compounds as substrates. The corresponding aliphatic, aromatic and allylic alcohols were obtained in excellent yields with catalyst loadings as low as 0.1-0.5 mol % at mild temperatures after very short reaction times. This protocol tolerates iPrOH and EtOH as hydrogen sources. Additionally, scale up to multi-gram amounts was performed without any loss of activity or selectivity. An outer-sphere mechanism has been proposed and the computed kinetics and thermodynamics of crotonaldehyde and 1-phenyl-but-2-en-one are in perfect agreement with the experiment.

Stereoselective synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc) and ureido-DNJNAc derivatives as new hexosaminidase inhibitors.

2-Acetamido-1,2-dideoxyiminosugars are selective and potent inhibitors of hexosaminidases and therefore show high therapeutic potential for the treatment of various diseases, including several lysosomal storage disorders. A stereoselective synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc), the iminosugar analog of N-acetylglucosamine, with a high overall yield is here described. This novel procedure further allowed accessing ureido-DNJNAc conjugates through derivatization of the endocyclic amine on a key pivotal intermediate. Remarkably, some of the ureido-DNJNAc representatives behaved as potent and selective inhibitors of ß-hexosaminidases, including the human enzyme, being the first examples of neutral sp(2)-iminosugar-type inhibitors reported for these enzymes. Moreover, the amphiphilic character of the new ureido-DNJNAc is expected to confer better drug-like properties.

E-Selective Manganese-Catalyzed Semihydrogenation of Alkynes with H2 Directly Employed or In Situ-Generated.

Selective semihydrogenation of alkynes with the Mn(I) alkyl catalyst fac-[Mn(dippe)(CO)3(CH2CH2CH3)] (dippe = 1,2-bis(di-iso-propylphosphino)ethane) as a precatalyst is described. The required hydrogen gas is either directly employed or in situ-generated upon alcoholysis of KBH4 with methanol. A series of aryl-aryl, aryl-alkyl, alkyl-alkyl, and terminal alkynes was readily hydrogenated to yield E-alkenes in good to excellent isolated yields. The reaction proceeds at 60 °C for directly employed hydrogen or at 60-90 °C with in situ-generated hydrogen and catalyst loadings of 0.5-2 mol %. The implemented protocol tolerates a variety of electron-donating and electron-withdrawing functional groups, including halides, phenols, nitriles, unprotected amines, and heterocycles. The reaction can be upscaled to the gram scale. Mechanistic investigations, including deuterium-labeling studies and density functional theory (DFT) calculations, were undertaken to provide a reasonable reaction mechanism, showing that initially formed Z-isomer undergoes fast isomerization to afford the thermodynamically more stable E-isomer.