Abstracts

2.1 Reduction of Aldehydes

N. Steinfeldt and K. Junge

Alcohols are valuable chemical intermediates and products that can be obtained by reduction of aldehydes. This chapter describes methods where the aldehyde reduction is performed in the liquid phase with hydrogen delivered directly from a cylinder or by hydrogen-donor molecules. Since they are both widely applied, both heterogeneous and homogeneous catalyzed reactions are considered.

Keywords: aldehydes • alcohols • reduction • hydrogenation • transfer hydrogenation • heterogeneous catalysis • homogeneous catalysis • liquid-phase reduction

2.2 Transfer Hydrogenation of Ketones to Alcohols

A. Matsunami, Y. Kayaki, and T. Ikariya

Transfer hydrogenation offers an alternative to hydrogenation using gaseous hydrogen, as well as a practical synthetic approach to enantiopure compounds. Alcohols, formic acid, and formate salts are often used as safe and nontoxic hydrogen sources in transition-metal catalyzed transfer hydrogenation systems. This chapter highlights effective transfer hydrogenation and asymmetric transfer hydrogenation of ketones catalyzed by transition-metal complexes. The reactions described in this section are classified according to the reducing agents employed and the type of ketone substrate.

Keywords: transfer hydrogenation • asymmetric transfer hydrogenation • ketones • esters • alcohols • propan-2-ol • formic acid • formate salts • metal-ligand cooperation • dynamic kinetic resolution • reduction

2.3 Catalytic Hydrogenation of Ketones

Q. Llopis, T. Ayad, P. Phansavath, and V. Ratovelomanana-Vidal

Catalytic hydrogenation using molecular hydrogen to reduce ketones is arguably one of the most efficient, practical, and environmentally responsible methods for the production of secondary alcohols, which are important building blocks for the synthesis of fine chemicals, pharmaceuticals, perfumes, and agrochemicals, as well as functional materials. This chapter, presents a non-exhaustive review of transition-metal-catalyzed homogeneous racemic as well as asymmetric hydrogenation of simple and functionalized ketones to give the corresponding secondary alcohols, with a focus on major advances in this important field from 2008 to late 2016.

Keywords: transition metals • asymmetric catalysis • homogeneous catalysis • carbon-hydrogen bonds • hydrogenation • ketones • secondary alcohols • enantioselectivity • diastereoselectivity • dynamic kinetic resolution • reduction

2.4 Hydrogenolysis of Aryl Ketones and Aldehydes, Benzylic Alcohols and Amines, and Their Derivatives

B. Ciszek and I. Fleischer

This chapter provides an overview of the hetero- and homogeneous metal-catalyzed hydrogenolysis of C=O, C-O, and C-N bonds at benzylic positions. This reaction constitutes an atom- and waste-economic alternative to traditional defunctionalization methods. It has found numerous applications in organic synthesis, including in the removal of protecting groups from alcohols and amines. Moreover, its role in the valorization of biomass feedstocks is being intensely investigated.

Keywords: hydrogenolysis • reduction • defunctionalization • deoxygenation • deprotection • aryl ketones • benzaldehydes • benzylic alcohols • benzylic amines • hydrogen • formic acid • palladium • nickel • ruthenium • cobalt • molybdenum • rhodium

2.5.1 Homogeneous Catalytic Hydrogenation of Carboxylic Acids, Anhydrides, Esters, Amides, and Acid Chlorides

Y. Shi, D. J. Cole-Hamilton, and P. C. J. Kamer

The homogeneous catalytic hydrogenation of carboxylic acids and their derivatives, such as esters, amides, and anhydrides, is a fundamental reaction of potential importance for the synthesis of important organic building blocks in the polymer and pharmaceutical industries. The corresponding alcohols, amines, or aldehydes can be obtained by using various metal/ligand systems together with molecular hydrogen.

Keywords: homogeneous catalysis • reduction • hydrogenation • carboxylic acids • esters • amides • acid chlorides • anhydrides • alcohols • amines • triphos ligands • pincer ligands • chemoselectivity • enantioselectivity • ruthenium • iron • manganese • cobalt • iridium

2.5.2 Heterogeneous Catalytic Hydrogenation of Carboxylic Acids, Anhydrides, Esters, Amino Acids, and Amides

M. Besson and C. Pinel

The reduction of carboxylic acids and their derivatives (i.e., anhydrides, esters, amino acids, and amides) is a highly relevant transformation in synthetic organic chemistry and for biomass conversion. Interest in this area has recently increased thanks to the large-scale production of bio-based platform molecules. This chapter describes methods for the hydrogenation of carboxylic acids and derivatives using heterogeneous catalysts. The methods selected have generally been reported within the last ten years, and the focus is on those approaches that give high selectivity toward the desired products and on those employing highly stable catalysts.

Keywords: hydrogenation • reduction • heterogeneous catalysis • carboxylic acids • carboxylic esters • alcohols • aldehydes • diols • amino alcohols • amines • carboxylic anhydrides • biomass-derived functionalized (di)acids • amino acids • amides • vapor-phase reduction • liquid-phase reduction

2.6 Reduction of Imines and Reductive Amination of Aldehydes and Ketones

C. Claver, I. PeÇafiel, M. Urrutigoïty, and P. Kalck

Amines are powerful building blocks in the chemical industry due to their high reactivity. They also find various applications in fine chemistry. In the context of sustainable chemistry, the hydrogenation of imines and reductive amination of aldehydes and ketones represent efficient tools to give direct access to amines. For the asymmetric hydrogenation of imines, many catalyst precursors containing a transition metal and chiral phosphorus- or nitrogen-based ligands give rise to high yields and enantioselectivities. The one-pot reductive amination reaction involves the condensation of carbonyl and amine groups, followed by the hydrogenation of the resulting imine or enamine, performed by either heterogeneous or homogeneous catalysis. Molecular hydrogen or organic donors providing hydrogen by transfer can be used in both reactions. The more economical and environmentally friendly catalysts based on iron or copper offer attractive options in these two synthetic pathways.

Keywords: imines • amines • carbonyl compounds • reduction • reductive amination • hydrogenation • transfer hydrogenation • metal catalysis • asymmetric hydrogenation • homogeneous catalysis • heterogeneous catalysis • enantioselectivity

2.7 Reduction of Nitro Compounds to Amines, Azo Compounds, Hydroxylamines, and Oximes, and Reduction of N-Oxides to Amines

P. Puylaert, A. Savini, and S. Hinze

Various catalytic strategies are discussed for the reduction of both aromatic and aliphatic nitro functionalities to the corresponding amines, including homogeneous and heterogeneous (transfer) hydrogenations, as well as the water–gas shift reaction. Chemoselectivity with respect to other reducible moieties (carbonyls, alkenes, alkynes) and hydrodehalogenation is taken into account. The isolation of azobenzenes, N-substituted hydroxylamines, and oximes, which are typically considered intermediates or byproducts in nitro reductions, is included as well. Finally, developments in the deoxygenation of N-oxides are addressed briefly.

Keywords: nitroaromatics • nitroaliphatics • reduction • deoxygenation • N-oxides • hydrogenation • transfer hydrogenation • water–gas shift reaction • anilines • amines • azobenzenes • N-substituted hydroxylamines • oximes • pyridines • chemoselectivity • scale-up • homogeneous catalysis • heterogeneous catalysis

2.8 Reduction of Azides

Y. Monguchi and H. Sajiki

This chapter covers recent progress in the catalytic hydrogenation and catalytic transfer hydrogenation of azides, including continuous-flow hydrogenation using heterogeneous catalysts, hydrogenative formylation, and hydrogenative alkylation for natural product synthesis. Recently developed catalysts for the chemoselective reduction of azides in the presence of other coexisting reducible functionalities are especially highlighted. Furthermore, a method for the selective semihydrogenation of alkynes to the corresponding alkenes leaving coexisting azides intact is also presented.

Keywords: catalytic hydrogenation • reduction • catalytic transfer hydrogenation • chemoselectivity • catalysts • azides • alkynes •...