Dehydrogenation as a substrate-activating strategy in homogeneous transition-metal catalysis.

Conventional oxidations of organic compounds formally transfer hydrogen atoms from the substrate to an acceptor molecule such as oxygen, a metal oxide, or a sacrificial olefin. In acceptorless dehydrogenation (AD) reactions, catalytic scission of C-H, N-H, and/or O-H bonds liberates hydrogen gas with no need for a stoichiometric oxidant, thereby providing efficient, nonpolluting activation of substrates. In addition, the hydrogen gas is valuable in itself as a high-energy, clean fuel. Here, we review AD reactions selectively catalyzed by transition metal complexes, as well as related transformations that rely on intermediates derived from reversible dehydrogenation. We delineate the methodologies evolving from this recent concept and highlight the effect of these reactions on chemical synthesis.

http://science.sciencemag.org/content/sci/341/6143/1229712.full.pdf

Applications of acceptorless dehydrogenation and related transformations in chemical synthesis.

Hydrogen autotransfer in the N-alkylation of amines and related compounds using alcohols and amines as electrophiles.

Amongst the many ways of constructing the amide bond, there has been a growing interest in the use of metal-catalysed methods for preparing this important functional group. In this tutorial review, highlights of the recent literature have been presented covering the key areas where metal catalysts have been used in amide bond formation. Acids and esters have been used in coupling reactions with amines, but aldehydes and alcohols have also been used in oxidative couplings. The use of nitriles and oximes as starting materials for amide formation are also emerging areas of interest. The use of carbon monoxide in the transition metal catalysed coupling of amines has led to a powerful methodology for amide bond formation and this is complemented by the addition of an aryl or alkenyl group to an amide typically using palladium or copper catalysts.

http://www.chtf.stuba.sk/~szolcsanyi/education/files/Organicka%20chemia%20II/Prednaska%208_Aminokyseliny%20a%20peptidy/Doplnkove%20studijne%20materialy/Amide%20bond%20formation/Metal-catalysed%20approaches%20to%20amide%20bond%20formation.pdf

Metal-catalysed approaches to amide bond formation

Heterogeneous Catalysts for the One-Pot Synthesis of Chemicals and Fine Chemicals

The alkylation of amines by alcohols has been achieved using 0.5 mol % [Ru(p-cymene)Cl2]2 with the bidentate phosphines dppf or DPEphos as the catalyst. Primary amines have been converted into secondary amines, and secondary amines into tertiary amines, including the syntheses of Piribedil, Tripelennamine, and Chlorpheniramine. N-Heterocyclization reactions of primary amines are reported, as well as alkylation reactions of primary sulfonamides. Secondary alcohols require more forcing conditions than primary alcohols but are still effective alkylating agents in the presence of this catalyst.

Ruthenium-catalyzed N-alkylation of amines and sulfonamides using borrowing hydrogen methodology.

Borrowing Hydrogen in Water and Ionic Liquids: Iridium-Catalyzed Alkylation of Amines with Alcohols

The alkylation of amines using alcohols with the borrowing hydrogen strategy is reviewed. The alkylation process generates water as the only by-product and is catalysed by transition metal complexes which temporarily oxidise the alcohol to a more reactive aldehyde.

Gareth W. Lamb

Papers

Ruthenium-catalyzed N-alkylation of amines and sulfonamides using borrowing hydrogen methodology.

Borrowing Hydrogen in Water and Ionic Liquids: Iridium-Catalyzed Alkylation of Amines with Alcohols

Borrowing hydrogen - C - N bond formation from alcohols

Borrowing hydrogen methodology for the conversion of alcohols into N-protected primary amines and in situ deprotection

Ruthenium-Catalyzed N-Alkylation of Amines and Sulfonamides Using Borrowing Hydrogen Methodology.