Zinc‐Catalyzed Asymmetric Hydrosilylation of Cyclic Imines: Synthesis of Chiral 2‐Aryl‐Substituted Pyrrolidines as Pharmaceutical Building Blocks

PPM Ir-f-phamidol-Catalyzed Asymmetric Hydrogenation of γ-Amino Ketones Followed by Stereoselective Cyclization for Construction of Chiral 2-Aryl-pyrrolidine Pharmacophores

Transition metal catalysts with a million turnovers and excellent selectivity are rarely reported but are crucial for the industrial manufacture of optical pure pharmaceuticals, natural products, and fine chemicals. In this paper, we report an unprecedented aninoic Ir-f-phamidol catalyst for asymmetric hydrogenation of γ-amino ketones followed by stereoselective cyclization for construction of valuable chiral 2-aryl-pyrrolidine pharmacophores. The Ir-f-phamidol catalyst showed up to 1,000,000 TON and >99% ee, as well as excellent tolerance of substrates and protecting groups, providing various chiral amino alcohol intermediates. Upon optimization of the conditions, the stereoselective cyclization reaction was highly smooth and efficient (quantitative conversions, 92 to >99% ee). Finally, this solution was applied in the preparation of high-value chiral entities containing such chiral 2-aryl-pyrrolidine pharmacophores.

Enantio-Complementary Synthesis of 2-Substituted Pyrrolidines and Piperidines via Transaminase-Triggered Cyclizations

Chiral N-heterocycles are a common motif in many active pharmaceutical ingredients; however, their synthesis often relies on the use of heavy metals. In recent years, several biocatalytic approaches have emerged to reach enantiopurity. Here, we describe the asymmetric synthesis of 2-substituted pyrrolidines and piperidines, starting from commercially available ω-chloroketones by using transaminases, which has not yet been comprehensively studied. Analytical yields of up to 90% and enantiomeric excesses of up to >99.5% for each enantiomer were achieved, which has not previously been shown for bulky substituents. This biocatalytic approach was applied to synthesize (R)-2-(p-chlorophenyl)pyrrolidine on a 300 mg scale, affording 84% isolated yield, with >99.5% ee.

N-Silylamines in catalysis: synthesis and reactivity

A summary of the catalytic synthesis and reactivity of N-silylated amines is presented. Dehydrocoupling of amines with silanes, hydrosilylation of imines and dealkenylative coupling of amines with vinylsilanes are three ways to achieve their catalytic syntheses. The resultant N-silylamines serve as substrates in a variety of reactions, including C-N and C-C bond forming reactions, and are preferred in transformations because of the facile Si-N hydrolytic cleavage to reveal free amine products upon reaction completion. This review highlights the distinct electronic properties of N-silyl amines, N-silyl imines and N-silyl enamines that result in complementary reactivity to that of parent non-silyl variants.

Efficient preparation of (R)-2-(2,5-difluorophenyl)pyrrolidine via a recycle process of resolution

An efficient preparation of (R)-2-(2,5-difluorophenyl)pyrrolidine ((R)-1) from the racemate based on a recycle process of resolution/racemization was described. In the process, the desired (R)-1 was obtained by resolution with D-malic acid in 95% EtOH. Meanwhile, the undesired (S)-1 could be racemized in the presence of potassium hydroxide in DMSO. After three times of recycle process, the desired freebase (R)-1 was obtained in a yield of 61.7% with excellent ee (98.4%).

On the application of 3d metals for C-H activation toward bioactive compounds: The key step for the synthesis of silver bullets

Several valuable biologically active molecules can be obtained through C-H activation processes. However, the use of expensive and not readily accessible catalysts complicates the process of pharmacological application of these compounds. A plausible way to overcome this issue is developing and using cheaper, more accessible, and equally effective catalysts. First-row transition (3d) metals have shown to be important catalysts in this matter. This review summarizes the use of 3d metal catalysts in C-H activation processes to obtain potentially (or proved) biologically active compounds.

Novel (S)-Selective Hydrolase from Arthrobacter sp. K5 for Kinetic Resolution of Cyclic Amines

Chiral 2-methylpiperidine (2-MPI) is an important building block that has potential for applications in pharmaceuticals and pesticides. In this study, we observed that the hydrolase in Arthrobacter sp. K5 exhibits high (S)-selectivity toward rac-N-pivaloyl-2-MPI to yield (S)-2-MPI with 80.2% enantiomeric excess (ee) in a 38.2% conversion. The hydrolase, which was identified by analyses of partial amino acid sequences of the purified enzyme and genome sequence of Arthrobacter sp. K5, exhibited moderate homology with amidohydrolases up to 67% (molinate hydrolase from Gulosibacter molinativorax). The hydrolase gene was overexpressed in Rhodococcus erythropolis. The recombinant cells produced (S)-2-MPI with 83.5% ee in a 48.4% conversion (E = 26.3) from 100 mM rac-N-pivaloyl-2-MPI. These results suggest the possibility of an efficient preparation of chiral 2-MPI in kinetic resolution.