Fast and Selective Hydroaminomethylation Using Xanthene‐Based Amino‐Functionalized Ligands

Abstract

Dedicated to Prof. Wilhelm Keim on the occasion of his 75 th birthdayIn both the bulk and fine chemical industries, amines are of great importance, for example as active pharmaceutical ingredients or building blocks for polymers. [1, 2] Easy and selective atom-efficient synthetic access to these intermediates, availability and price of starting materials, and waste reduction have been important issues over the past decades. In this perspective, hydroaminomethylation (HAM), is a promising reaction among newly developed catalytic methods to synthesize amines, alongside such reactions as palladium-catalyzed amination of aryl halides, [3] hydroamination, [4] and reductive amination, [5] which fulfill the aforementioned requirements.Hydroaminomethylation, which was first discovered by Reppe in 1949, [6] is a transition metal-catalyzed cascade reaction, combining, in one pot, an alkene hydroformylation and a reductive amination of the intermediate aldehyde with an amine (secondary, primary, or ammonia), leading to the desired amine product (Scheme 1). Although this reaction has been Supporting information for this article is available on the WWW under http://dx.

Interplay between Cationic and Neutral Species in the Rhodium‐Catalyzed Hydroaminomethylation Reaction

“…7 On the other hand, [Rh(cod) 2 ]BF 4 should generate the [Rh(H) 2 (S) 2 (PP)] + species (S=solvent), which is an active species in hydrogenation 11. Recently, Vogt et al 10e. proposed the simultaneous use of cationic and neutral rhodium precursors in order to increase both catalytic activity and amine selectivity.…”

Formation of Acetals under Rhodium‐Catalyzed Hydroformylation Conditions in Alcohols

“…We reported recently on the excellent activities and selectivities obtained in hydroaminomethylation using a combination of a rhodium source and the DPX ligand (Scheme ) 4a. Ethanol and methanol were the most suitable solvents for this transformation.…”

“…Representing a potential atom efficient route to amines, we are interested in the hydroaminomethylation (HAM),2,3 a cascade reaction involving hydroformylation and a reductive amination step (see Scheme ) 4. This reaction proceeds faster and with better selectivities using alcohols as co‐solvent 4a. In order to understand the role of the alcohol in the catalytic cycle, we decided to investigate in the first place the hydroformylation reaction in alcohol solvents.…”

Recent Advances in Amine Synthesis by Catalytic Hydroaminomethylation of Alkenes

“…[21] Dipyrrolylphosphine moieties have also been introduced on the xanthene backbone by Vogt et al, [22] who investigated the activity of the three new ligands 17, 18, and 19 (Scheme 4) with c values comparable to those of phosphites in the hydroaminomethylation of oct-1ene with piperidine (Scheme 6). It is well known that p-acidic ligands afford high activities in rhodium-catalyzed hydroformylation.…”

“…It is well known that p-acidic ligands afford high activities in rhodium-catalyzed hydroformylation. [21] Dipyrrolylphosphine moieties have also been introduced on the xanthene backbone by Vogt et al, [22] who investigated the activity of the three new ligands 17, 18, and 19 (Scheme 4) with c values comparable to those of phosphites in the hydroaminomethylation of oct-1ene with piperidine (Scheme 6). Ligand 17 gave more satisfactory results, with a n/iso ratio of 12.3 and 99.5 % amine selectivity, starting from 0.1 mol % of the [Rh(COD) 2 ]BF 4 precursor in toluene/MeOH solvent mixture.…”