Chiral‐Organotin‐Catalyzed Kinetic Resolution of Vicinal Amino Alcohols

Organotin(IV) compounds catalyzed cyanide-free synthesis of α-iminonitriles

Two polydentate pro-ligands (H2L1 and H3L2) have been reacted with different organotin(IV) halides such as Ph2SnCl2, (t-Bu)2SnCl2, and (n-Bu)2SnCl2 to synthesize six organotin(IV) compounds, [R2Sn(L1)] (R = Ph (1), t-Bu (2), n-Bu (3)) and [R2Sn(HL2)] (R = Ph (4), t-Bu (5), n-Bu (6)), respectively. All organotin(IV) compounds were characterized by FT-IR spectroscopy, 1H, 13C{1H}, and 119Sn{1H} NMR spectroscopy, HR-MS spectrometry, and single-crystal X-ray diffraction analysis. The single-crystal X-ray diffraction analyses reveal that all compounds contain a penta-coordinated tin atom except 1. Compound 1 is hexacoordinated. All organotin compounds show catalytic efficiency towards the synthesis of α-iminonitriles, with a maximum yield of up to 88%. The α-iminonitriles are synthesized from trans-β-nitrostyrene derivatives and 2-aminopyridine derivatives without using any cyanating agent.

Asymmetric Amination of 1,2-Diol through Borrowing Hydrogen: Synthesis of Vicinal Amino α-Tertiary Alcohol

Methods to prepare vicinal amino alcohols are important because of their presence in biologically active compounds. Despite the development of various methods for vicinal amino alcohol synthesis, C(sp3)-rich oxygen-containing β-amine compounds continue to pose great challenge. While ring-opening reaction of epoxides with amine nucleophile is the prime method for vicinal amino alcohol preparation, epoxides are highly reactive and sometimes difficult to make, resulting in drawbacks regarding selectivity of this approach. Here, we report a catalytic enantio-convergent amination of α-tertiary 1,2-diols for the efficient access to vicinal amino α-tertiary alcohols. The racemic α-tertiary 1,2-diol substrates of different alkyl/aryl or alkyl/alkyl backbone, can be converted to chiral vicinal amino α-tertiary alcohols through diphenyl phosphate-mediated RuCl3 catalysed asymmetric borrowing hydrogen (ABH) pathway. This simple ABH reaction can be scaled up to the synthesis of chiral ligands, synthetic intermediates, and other medicinally-relevant compounds. Overall, this catalytic redox-neutral procedure broadens the scope of Ru-catalysed amination of alcohols and discloses an underexplored step- and atom-economical synthetic strategy for the synthesis of vicinal amino α-tertiary alcohols and provides a practicable alternative to the present benchmark procedures.

Nonactivated Aziridine Synthesis by Intermolecular Polarity-Mismatched Carboamination of Unactivated Alkenes with Unactivated Alkyl Halides

A general intermolecular polarity-mismatched carboamination reaction of unactivated alkenes with unactivated alkyl halides has been developed. A series of nonactivated alkyl-substituted aziridines were constructed in exclusive regioselectivity. The dual polarity-mismatched mechanism might be involved.

Brønsted-Acid-Catalyzed Enantioselective Desymmetrization of 1,3-Diols: Access to Chiral β-Amino Alcohol Derivatives

Herein, we describe a Brønsted-acid-catalyzed enantioselective desymmetrization of 1,3-diols with alkynes through a hydroalkoxylation/hydrolysis process. The reaction leads to the atom-economical synthesis of valuable chiral β-amino alcohols under mild reaction conditions. Further synthetic transformations based on the β-amino alcohol moiety provide divergent approaches toward chiral N-containing heterocycles.

Iron-Catalyzed Intermolecular Oxyamination of Terminal Alkenes Promoted by HFIP Using Hydroxylamine Derivatives

An atom-economical intermolecular iron-catalyzed oxyamination of alkenes is described herein. The insertion of oxygenated and nitrogenated moieties from the hydroxylamine substrate was observed with full regio- and chemo-selectivity for terminal alkenes in good yields. HFIP as a solvent appeared to have a synergistic effect with the iron catalyst to promote the formation of the oxyaminated products. Preliminary mechanistic studies suggest a pathway going through an aziridination reaction followed by an in situ ring opening.

Multienzyme Redox System with Cofactor Regeneration for Cyclic Deracemization of Sulfoxides

Optically pure sulfoxides are noteworthy compounds applied in a wide range of industrial fields; however, the biocatalytic deracemization of racemic sulfoxides is challenging. Herein, a high-enantioselective methionine sulfoxide reductase A (MsrA) was combined with a low-enantioselective styrene monooxygenase (SMO) for the cyclic deracemization of sulfoxides. Enantiopure sulfoxides were obtained in >90% yield and with >90% enantiomeric excess ( ee ) through dynamic "selective reduction and non-selective oxidation" cycles. The cofactors of MsrA and SMO were subsequently regenerated by the cascade catalysis of three auxiliary enzymes through the consumption of low-cost D-glucose. Moreover, this "one-pot, one-step" cyclic deracemization strategy exhibited a wide substrate scope toward various aromatic, heteroaromatic, alkyl and thio-alkyl sulfoxides. This system proposed an efficient strategy for the green synthesis of chiral sulfoxide .

Palladium-Catalyzed trans-Hydroalkoxylation: Counterintuitive Use of an Aryl Iodide Additive to Promote C–H Bond Formation

We report an enantioselective palladium-catalyzed trans-hydroalkoxylation of propargylic amines with a trifluoroacetaldehyde-derived tether to build chiral oxazolidines. Diastereoselective hydrogenation using a heterogeneous palladium catalyst then gave access to protected benzylic amino alcohols in 45–87% yields and 84–94% ee values. Hydroalkoxylation of the alkynes required a catalytic amount of aryl iodide, highlighting the counterintuitive key role played by a putative Pd(II)/ArI oxidative addition complex to promote oxypalladation/protodemetalation.

A highly enantioselective approach towards optically active γ-amino alcohols by tin-catalyzed kinetic resolution of 1,3-amino alcohols

A highly enantioselective kinetic resolution of racemic 1,3-amino alcohols via O-Acylation was achieved using a chiral organotin as the catalyst. Alkyl- and aryl-substituted 1,3-amino alcohols were resolved with excellent efficiencies to afford the recovered 1,3-amino alcohols and acylative products with high enantioselectivities, with s factors up to >600. Notably, the chiral organotin catalyst was more selective for anti-1,3-amino alcohols than for syn-isomers. A Gram-scale reaction with loading using 2 mol% catalysts demonstrated the utility of this protocol.

Kinetic Resolution of Tertiary Alcohols by Chiral Organotin-Catalyzed O-Acylation

A novel highly enantioselective method for the kinetic resolution of racemic tertiary alcohols has been achieved through chiral organotin-catalyzed intermolecular acylation of the hydroxyl group. This process has demonstrated a broad substrate scope (both alkyl- and aryl-substituted tertiary alcohols) with high enantioselectivity under mild reaction conditions, affording the corresponding products and the recovered tertiary alcohols with high enantioselectivities, with s factors up to >200.

Kinetic resolution of N-aryl β-amino alcohols via asymmetric aminations of anilines

An efficient kinetic resolution of N-aryl β-amino alcohols has been developed via asymmetric para-aminations of anilines with azodicarboxylates enabled by chiral phosphoric acid catalysis. Broad substrate scope and high kinetic resolution performances were afforded with this method. Control experiments supported the critical roles of the NH and OH group in these reactions.

Catalytic asymmetric oxidative carbonylation-induced kinetic resolution of sterically hindered benzylamines to chiral isoindolinones

A highly enantioselective kinetic resolution of sterically hindered benzylamines has been achieved for the first time through transition-metal-catalyzed oxidative carbonylation, in which the new KR strategy offered a new approach to afford chiral isoindolinones (er up to 97 : 3) and the origin of chemoselectivity and stereoselectivity was confirmed by density functional theory (DFT) calculations.

Enantioselective Carboetherification/Hydrogenation for the Synthesis of Amino Alcohols via a Catalytically Formed Chiral Auxiliary

Chiral auxiliaries and asymmetric catalysis are the workhorses of enantioselective transformations, but they still remain limited in terms of either efficiency or generality. Herein, we present an alternative strategy for controlling the stereoselectivity of chemical reactions. Asymmetric catalysis is used to install a transient chiral auxiliary starting from achiral precursors, which then directs diastereoselective reactions. We apply this strategy to a palladium-catalyzed carboetherification/hydrogenation sequence on propargylic amines, providing fast access to enantioenriched chiral amino alcohols, important building blocks for medicinal chemistry and drug discovery. All stereoisomers of the product could be accessed by the choice of ligand and substituent on the propargylic amine, leading to a stereodivergent process.