Yasushi Imada

Aerobic Reduction of Olefins by In Situ Generation of Diimide with Synthetic Flavin Catalysts

A versatile reducing agent, diimide, can be generated efficiently by the aerobic oxidation of hydrazine with neutral and cationic synthetic flavin catalysts 1 and 2. This technique provides a convenient and safe method for the aerobic reduction of olefins, which proceeds with 1 equiv of hydrazine under an atmosphere of O(2) or air. The synthetic advantage over the conventional gas-based method has been illustrated through high hydrazine efficiency, easy and safe handling, and characteristic chemoselectivity. Vitamin B(2) derivative 6 acts as a highly practical, robust catalyst for this purpose because of its high availability and recyclability. Association complexes of 1b with dendritic 2,5-bis(acylamino)pyridine 15 exhibit unprecedented catalytic activities, with the reduction of aromatic and hydroxy olefins proceeding significantly faster when a higher-generation dendrimer is used as a host pair for the association catalysts. Contrasting retardation is observed upon similar treatment of non-aromatic or non-hydroxy olefins with the dendrimer catalysts. Control experiments and kinetic studies revealed that these catalytic reactions include two independent, anaerobic and aerobic, processes for the generation of diimide from hydrazine. Positive and negative dendrimer effects on the catalytic reactions have been ascribed to the specific inclusion of hydrazine and olefinic substrates into the enzyme-like reaction cavities of the association complex catalysts.

Palladium(O) catalyzed azidation and amination of allyl acetates. Selective synthesis of allyl azides and primary allylamines

Abstract Palladium catalyzed reaction of allyl acetates with azide ion gives allyl azides, which are readily converted into the corresponding primary allylamines upon treatment with PPh 3 /NaOH.

Neutral Flavins: Green and Robust Organocatalysts for Aerobic Hydrogenation of Olefins

Various olefins can be hydrogenated quantitatively with neutral flavin 2 catalysts in the presence of 1-2 equiv of hydrazine under 1 atm of O(2). Vitamin B(2) derivative 2g acts as a highly efficient and robust catalyst for the present environmentally benign process producing water and nitrogen gas as the only waste products.

Palladium(0)-catalyzed carbonylation of allyl phosphates and allyl acetates. Selective synthesis of β,γ-unsaturated esters

Abstract Palladium catalyzed carbonylations of allyl phosphates and allyl acetates give β,γ-unsaturated esters efficiently. The latter reaction requires bromide ion as a co-catalyst.

Palladium-catalyzed Carbonylation of Allylamines. Synthesis of β,γ-unsaturated amides by one-carbon homologation of Allylamines

Abstract Palladium-catalyzed carbonylation of allylamines under CO (50atm) at 110°C proceeds highly efficiently to give the corresponding β,γ-unsaturated amides. The carbonylation occurs at the less substituted carbon of allyl units to give linear amides with high regioselectivity. The reaction can be rationalized by assuming the mechanism which involves oxidative addition of palladium (0) species to allylamines to give π-allylpalladium complexes, insertion of carbon monoxide to give acylpalladium species, and amidation.

Palladium(o)-catalyzed hydroxylamination of allyl esters: Synthesis of n-allylhydroxylamines and secondary allylamines

Abstract Palladium-catalyzed reaction of allyl esters with hydroxylamines gives N-allylhydroxylamines, which are readily converted into secondary allylamines upon treatment with zinc powder in a dilute HCl solution.

Rhodium catalyzed hydrogenation of nitrogen heteroaromatics under water gas shift conditions. Selective synthesis of 1,2,3,4-tetrahydroquinolines and N-formyl-1,2,3,4-tetrahydroisoquinolines

Abstract Quinolines and isoquinolines are hydrogenated selectively in the nitrogen-containing ring by means of carbon monoxide and water in the presence of catalytic amount of rhodium carbonyl cluster.

Synthesis of (R)- and (S)-3-(tert-butyldimethylsilyloxy)-1-pyrroline N-oxides — chiral nitrones for synthesis of biologically active pyrrolidine derivative, Geissman-Waiss lactone

Tungstate-catalyzed oxidation of O-tert-butyldimethylsilyl (O-TBDMS) protected (R)-3-hydroxypyrrolidine ((R)-2), derived from trans-4-hydroxy-l-proline, gave O-TBDMS protected (R)-3-hydroxy-1-pyrroline N-oxide ((R)-1), which is a new chiral precursor for the synthesis of Geissman-Waiss lactone. The enantiomeric nitrone (S)-1 was also prepared by the oxidation of (S)-2 derived from l-malic acid.

Palladium-catalyzed asymmetric alkoxycarbonylation of allyl phosphates

Palladium-catalyzed alkoxycarbonylation of allyl phosphates proceeds with high efficiency affording the corresponding β,γ-unsaturated esters stereoselectively with inversion of configuration at the allylic carbon center. Palladium complexes bearing chiral monodentate phoshine ligands are effective catalysts for asymmetric allylic carbonylation of cyclohex-2-en-1-yl phosphates 1 to give optically active cyclohex-2-ene-1-carboxylates 2 in moderate enantiomeric excesses.

Aza- and oxacarbonylations of allyl phosphates catalyzed by rhodium carbonyl cluster. Selective synthesis of β,γ-unsaturated amides, esters, and acids

Abstract Rhodium-catalyzed carbonylation of allyl phosphates under CO (20 atm) at 50°C proceeds very efficiently in the presence of amines, alcohols, and water to give the corresponding β,γ-unsaturated amides, esters, and acids, respectively. These carbonylations occur with high regioselectivity at the less substituted carbon of allyl unit to give linear β,γ-unsaturated acid derivatives.