On the selectivity of deprotection of benzyl, mpm (4-methoxybenzyl) and dmpm (3,4-dimethoxybenzyl) protecting groups for hydroxy functions

The last two decades have seen an impressive improvement of the use of iron as a fascinating and valuable alternative transition metal in homogeneous catalysis in terms of sustainability and economy. It was efficiently used in catalytic organic synthetic transformations, which in particular include the reduction of unsaturated bonds. This review summarizes the fast development and the recent advances in selective reductions of olefins, alkynes, carbonyl and carboxylic derivatives, imines, and nitro compounds promoted by iron catalysts. The topical hydrogen-borrowing reactions and hydroboration of unsaturated compounds are also reported. It is hoped that this account not only provides an overview of the state of the art in iron catalysis but also stimulates the development of superior greener catalytic systems in the near future.

Iron Catalysis in Reduction and Hydrometalation Reactions.

Quinones are common stoichiometric reagents in organic chemistry. Para-quinones with high reduction potentials, such as DDQ and chloranil, are widely used and typically promote hydride abstraction. In recent years, many catalytic applications of these methods have been achieved by using transition metals, electrochemistry, or O2 to regenerate the oxidized quinone in situ. Complementary studies have led to the development of a different class of quinones that resemble the ortho-quinone cofactors in copper amine oxidases and mediate the efficient and selective aerobic and/or electrochemical dehydrogenation of amines. The latter reactions typically proceed by electrophilic transamination and/or addition-elimination reaction mechanisms, rather than hydride abstraction pathways. The collective observations show that the quinone structure has a significant influence on the reaction mechanism and has important implications for the development of new quinone reagents and quinone-catalyzed transformations.

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Quinone-Catalyzed Selective Oxidation of Organic Molecules

A new approach is developed for hydrogenolytic ring opening of biobased 5-hydroxymethylfurfural (HMF), dehydration product of hexoses, towards 1,6-hexanediol (HDO) under atmospheric pressure. The highest yield of HDO, 43%, is achieved over reusable Pd/zirconium phosphate (ZrP) catalyst at 413 K in the presence of formic acid as hydrogen source. In comparison with various Bronsted and/or Lewis acidic supports, the specific Bronsted acidity on ZrP support effectively accelerated the cleavage of C-O bond in a furan ring.

Direct Synthesis of 1,6‐Hexanediol from HMF over a Heterogeneous Pd/ZrP Catalyst using Formic Acid as Hydrogen Source

1 Preparation and Characterization of Lignin-Carbohydrate Complexes.- 2 Location of Lignin Moieties Along Polysaccharide Chains in Lignin-Carbohydrate Complexes.- 3 Formation of Lignin-Carbohydrate-Complex Micelles and Pectin/Lignin/Hemicelluloses.- 4 Analysis of Native Bonds Between Lignin and Carbohydrate by Specific Chemical Reactions.- 5 Residual Lignin in Alkaline Pulps.- 6 Functions of Lignin-Carbohydrate Complexes.- 7 Microbial Degradation of Lignin-Carbohydrate Complexes.- 8 Condensation of Lignins with Carbohydrates in Concentrated Sulfuric Acid.- References.

Association Between Lignin and Carbohydrates in Wood and Other Plant Tissues

Transfer hydrogenation and transfer hydrogenolysis: VIII. Hydrogen transfer from amines to olefins catalyzed by heterogeneous and homogeneous catalysts

Transfer hydrogenation and transfer hydrogenolysis—21 : Dehydrogenation of alcohols by quinones

Transfer hydrogenation and transfer hydrogenolysis

The selective hydrogenation of methyl linoleate was studied using various organic compounds as hydrogen sources in the presence of homogeneous and metallic palladium catalysts. Complete selectivity to monoenes and relatively little formation of isolatedtrans double bonds were realized by the hydrogen transfer from L-ascorbic acid at 47% conversion of starting material to hydrogenation products. The hydrogenation bytrans-1,2-cyclohexanediol catalyzed by RuH2(PPh3)4 also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH2(PPh3)4, also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH2(PPh3)4, the presence of these hydroxy compounds increased the isomerization of methyl elaidate tocis-monoenes.

Transfer hydrogenation and transfer hydrogenolysis: XII. Selective hydrogenation of fatty acid methyl esters by various hydrogen donors

In the homogeneous hydrogenation of eight membered cyclo-olefins, o- and p-dihydroxybenzene were superior to alcohols as hydrogen donors, and FeCl2(PPh3)2 and FeBr2(PPh3)2 were the most active catalysts of the complexes MX2(PPh3)2, where M is FeII, CoII, and NiII, and X is Cl–, Br–, and I–.

Takeshi Nishiguchi

Papers

Transfer hydrogenation and transfer hydrogenolysis: VIII. Hydrogen transfer from amines to olefins catalyzed by heterogeneous and homogeneous catalysts

Transfer hydrogenation and transfer hydrogenolysis—21 : Dehydrogenation of alcohols by quinones

Transfer hydrogenation and transfer hydrogenolysis

Transfer hydrogenation and transfer hydrogenolysis: XII. Selective hydrogenation of fatty acid methyl esters by various hydrogen donors

Homogeneous transfer-hydrogenation of olefins catalysed by FeII, CoII, and NiII complexes: o- and p-dihydroxybenzene as hydrogen donors