Recent advances in catalytic C-N bond formation: a comparison of cascade hydroaminomethylation and reductive amination reactions with the corresponding hydroamidomethylation and reductive amidation reactions

Scandium-catalysed intermolecular hydroaminoalkylation of olefins with aliphatic tertiary amines

A homoleptic scandium trialkyl complex in combination with a borate compound served as an excellent catalyst for the C-H addition of aliphatic tertiary amines to olefins. This highly regiospecific, 100% atom efficient C-H bond alkylation reaction was applicable to a wide variety of tertiary amines and olefins, including functionalised styrenes and unactivated α-olefins. This work represents the first example of rare-earth catalysed olefin hydroaminoalkylation and also the first example of catalytic C-H addition of aliphatic tertiary amines to olefins with any catalyst.

Carbon Dioxide Transformation in Imidazolium Salts: Hydroaminomethylation Catalyzed by Ru-Complexes

The catalytic species generated by dissolving Ru3 (CO)12 in the ionic liquids 1-n-butyl-3-methyl-imidazolium chloride or 1-n-butyl-2,3-dimethyl-imidazolium chloride are efficient multifunctional catalysts for: (a) reverse water-gas shift, (b) hydroformylation of alkenes, and (c) reductive amination of aldehydes. Thus the reaction of alkenes with primary or secondary amines (alkene/amine, 1:1) under CO2 /H2 (1:1) affords the hydroaminomethylations products in high alkene conversions (up to 99 %) and selectivities (up to 96 %). The reaction proceeds under relatively mild reaction conditions (120 °C, 60 bar=6 MPa) and affords selectively secondary and tertiary amines. The presence of amine strongly reduces the alkene hydrogenation competitive pathway usually observed in the hydroformylation of terminal alkenes by Ru complexes. The catalytic system is also highly active for the reductive amination of aldehydes and ketones yielding amines in high yields (>90 %).

Synthesis of α-Amidoketones from Vinyl Esters via a Catalytic/Thermal Cascade Reaction

A straightforward, modular, and atom-efficient method is reported for the synthesis of α-amidoketones from vinyl esters via a cascade reaction including hydroformylation, condensation with a primary amine, and a rearrangement step giving water as the only byproduct. The reaction sequence can be performed in one pot or as a three-step procedure. The synthetic applicability is demonstrated by the preparation of different α-amidoketones in moderate to good yields.

Ruthenium-Catalyzed Transfer Hydrogenation for C-C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs

Merging the chemistry of transfer hydrogenation and carbonyl or imine addition, a broad new family of redox-neutral or reductive hydrohydroxyalkylations and hydroaminomethylations have been developed. In these processes, hydrogen redistribution between alcohols and π-unsaturated reactants is accompanied by C-C bond formation, enabling direct conversion of lower alcohols to higher alcohols. Similarly, hydrogen redistribution between amines to π-unsaturated reactants results in direct conversion of lower amines to higher amines. Alternatively, equivalent products of hydrohydroxyalkylation and hydroaminomethylation may be generated through the reaction of carbonyl compounds or imines with π-unsaturated reactants under the conditions of 2-propanol-mediated reductive coupling. Finally, using vicinally dioxygenated reactants, that is, diol, ketols, or diones, successive transfer hydrogenative coupling occurs to generate 2 C-C bonds, resulting in products of formal [4+2] cycloaddition.

Diene hydroaminomethylation via ruthenium-catalyzed C-C bond forming transfer hydrogenation: beyond carbonylation

Under the conditions of ruthenium catalyzed transfer hydrogenation using 2-propanol as terminal reductant, 1,3-dienes engage in reductive C-C coupling with formaldimines obtained in situ from 1,3,5-tris(aryl)-hexahydro-1,3,5-triazines to form homoallylic amines. Deuterium labelling studies corroborate a mechanism involving reversible diene hydroruthenation to form an allylruthenium complex that engages in turn-over limiting imine addition. Protonolysis of the resulting amidoruthenium species releases product and delivers a ruthenium alkoxide, which upon β-hydride elimination closes the catalytic cycle. These transformations, which include enantioselective variants, represent the first examples of diene hydroaminomethylation.

Catalytic N-Alkylation of Amines Using Carboxylic Acids and Molecular Hydrogen

A convenient, practical and green N-alkylation of amines has been accomplished by applying readily available carboxylic acids in the presence of molecular hydrogen. Applying an in situ formed ruthenium/triphos complex and an organic acid as cocatalyst, a broad range of alkylated secondary and tertiary amines are obtained in good to excellent yields. This novel method is also successfully applied for the synthesis of unsymmetrically substituted N-methyl/alkyl anilines through a direct three-component coupling reaction of the corresponding amines, carboxylic acids, and CO2 as a C1 source.

Rhodium-catalyzed hydroaminomethylation of cyclopentadiene

The substance class of amines is highly relevant for chemical and pharmaceutical industries. A one-step rhodium catalyzed direct route from cyclopentadiene to saturated C₆-amines is presented via hydroaminomethylation.