Synthesis of Allylic Amines by Asymmetric Transfer Hydrogenation of α,β-Unsaturated N-(tert-Butylsulfinyl)imines

Synthesis of α,γ-Chiral Trifluoromethylated Amines through the Stereospecific Isomerization of α-Chiral Allylic Amines

Chiral γ-branched aliphatic amines are present in a large number of pharmaceuticals and natural products. However, enantioselective methods to access these compounds are scarce and mainly rely on the use of designed chiral transition-metal complexes. Herein, we combined an organocatalytic method for the stereospecific isomerization of chiral allylic amines with a diastereoselective reduction of the chiral imine/enamine intermediates, leading to γ-trifluoromethylated aliphatic amines with two noncontiguous stereogenic centers, in excellent yields and high diastereo- and enantioselectivities. This approach has been used with primary amine substrates. This approach also provides a new synthetic pathway to chiral trifluoromethylated scaffolds, of importance in medicinal chemistry. Additionally, a gram-scale reaction demonstrates the applicability of this synthetic procedure.

PQQ-dependent Dehydrogenase Enables One-pot Bi-enzymatic Enantio-convergent Biocatalytic Amination of Racemic sec-Allylic Alcohols

The asymmetric amination of secondary racemic allylic alcohols bears several challenges like the reactivity of the bi-functional substrate/product as well as of the α,β-unsaturated ketone intermediate in an oxidation-reductive amination sequence. Heading for a biocatalytic amination cascade with a minimal number of enzymes, an oxidation step was implemented relying on a single PQQ-dependent dehydrogenase with low enantioselectivity. This enzyme allowed the oxidation of both enantiomers at the expense of iron(III) as oxidant. The stereoselective amination of the α,β-unsaturated ketone intermediate was achieved with transaminases using 1-phenylethylamine as formal reducing agent as well as nitrogen source. Choosing an appropriate transaminase, either the (R)- or (S)-enantiomer was obtained in optically pure form (>98 % ee). The enantio-convergent amination of the racemic allylic alcohols to one single allylic amine enantiomer was achieved in one pot in a sequential cascade.

A diversity of recently reported methodology for asymmetric imine reduction

This review describes recent developments in enantioselective imine reduction, including related substrates in which a CN bond is the target for reduction, and in situ methods.

Sequential Two-Step Stereoselective Amination of Allylic Alcohols through the Combination of Laccases and Amine Transaminases

A sequential two-step chemoenzymatic methodology for the stereoselective synthesis of (3E)-4-(het)arylbut-3-en-2-amines in a highly selective manner and under mild reaction conditions is described. The approach consists of oxidation of the corresponding racemic alcohol precursors by the use of a catalytic system made up of the laccase from Trametes versicolor and the oxy-radical TEMPO, followed by the asymmetric reductive bio-transamination of the corresponding ketone intermediates. Optimisation of the oxidation reaction, exhaustive amine transaminase screening for the bio-transaminations and the compatibility of the two enzymatic reactions were studied in depth in search of a design of a compatible sequential cascade. This synthetic strategy was successful and the combinations of enzymes displayed a broad substrate scope, with 16 chiral amines being obtained in moderate to good isolated yields (29-75 %) and with excellent enantiomeric excess values (94 to >99 %). Interestingly, both amine enantiomers can be achieved, depending on the selectivity of the amine transaminase employed in the system.

Nickel-Catalyzed Chemoselective Asymmetric Hydrogenation of α,β-Unsaturated Ketoimines: An Efficient Approach to Chiral Allylic Amines

An efficient synthetic route to chiral allylic amines has been developed by nickel/(S,S)-Ph-BPE complex catalyzed chemoselective asymmetric hydrogenation of α,β-unsaturated ketoimines. Varieties of α,β-unsaturated ketoimines have been well tolerated in this transformation to give chiral allylic amines with high yields and excellent ee values (up to 99% yield, up to 99% ee). A gram-scale reaction with 0.2 mol % catalyst loading has also been achieved.

Iridium-catalyzed diastereoselective amination of alcohols with chiral tert-butanesulfinamide by the use of a borrowing hydrogen methodology

An iridium-catalyzed diastereoselective amination of alcohols with chiral tert-butanesulfinamide was developed under basic conditions, affording the optically active secondary sulfinamides in high yields and diastereoselectivities. The removal of the sulfinyl group from sulfonamides allowed a facile access to a wide range of α-chiral primary amines. This synthetic strategy was further applied in the synthesis of the marketed pharmaceuticals (S)-rivastigmine and NPS R-568.