Fe(OTf) 3 -catalyzed tandem Meyer-Schuster rearrangement/intermolecular hydroamination of 3-aryl propargyl alcohols for the synthesis of acyclic β-Aminoketones

Enantioselective Synthesis of α-Quaternary Isochromanes by Oxidative Aminocatalysis and Gold Catalysis

A novel strategy that combines oxidative aminocatalysis and gold catalysis allows the preparation of chiral α-quaternary isochromanes, a motif that is prevalent in natural products and synthetic bioactive compounds. In the first step, α-branched aldehydes and propargylic alcohols are transformed into α-quaternary ethers with excellent optical purities (>90 % ee) via oxidative umpolung with DDQ and an amino acid-derived primary amine catalyst. Subsequent gold(I)-catalyzed intramolecular hydroarylation affords the isochromane products with retention of the quaternary stereocenter. A second approach explores the use of allylic alcohols as reaction partners for the oxidative coupling to furnish α-quaternary ethers with generally lower enantiopurities. Stereoretentive cyclization to isochromane products is achieved via intramolecular Friedel-Crafts type alkylation with allylic acetates as a reactive handle. A number of synthetic elaborations and a biological study on these α-quaternary isochromanes highlight the potential applicability of the presented method.

Bi(OTf)3-Catalyzed Alkyl-Intercepted Meyer-Schuster Rearrangement of Propargylic Alcohols for the Synthesis of 1,2,3,5-Tetrasubstituted Pentane-1,5-diones

An alkyl intercepted Meyer-Schuster rearrangement reaction with α,β-unsaturated ketones as the electrophiles was first investigated, which provided a facile method to construct 2-methylene-pentane-1,5-diones. Then the in situ generated 2-methylene-pentane-1,5-diones underwent a Michael addition to give diverse 2-malononitrile methyl substituted pentane-1,5-diones in a one-pot fashion. This transformation was reliable on a gram scale. The high yield, convenient experimental operation, and 100% atom economy made it a valuable method for the construction of 1,2,3,5-tetrasubstituted pentane-1,5-dione derivatives.

Bi(OTf)3 -catalyed One-pot Synthesis of α-Halo-β-amino Ketones and Acyl Aziridines from 3-Aryl Propargyl Alcohols

A Bi(OTf)₃ -catalyed reaction of 3-aryl propargyl alcohols with sulfonamide and halogen source was firstly investigated, which provided a facile route for the synthesis of a large variety of α-halo-β-amino ketones. The key intermediates, β-amino ketones, were obtained through tandem Meyer-Schuster rearrangement reaction of propargyl alcohols and intermolecular Michael addition of α, β-unsaturated ketones and sulfonamide. Then the in situ generated α-halo-β-amino ketones underwent the base-promoted intramolecular cyclization to give diverse acyl aziridines in a one-pot fashion. These transformations are reliable on a large scale. The high yields and convenient experimental operations make it a valuable method for the construction of α-halo-β-amino ketones and acyl aziridine derivatives.

Acid-Mediated Denitrogenation/Rearrangement/Coupling of ­Benzyl Azides with Triazolyl-Substituted Cycloalkanones

Organic molecules containing α-triazolyl or β-amino cyclic ketone fragments have been individually proven to show good bioactivities and to be useful in asymmetric and pharmaceutical syntheses. A triflic acid-promoted simple and efficient method for the synthesis of unsymmetrical α-triazolyl-α′-(aminomethyl)cycloalkanones from benzyl azides and α-triazolylcycloalkanones has been developed. A series of unsymmetrical α,α′-disubstituted cycloalkanones were obtained with high syn-diastereoselectivity and up to 82% yield. Examination of the reaction mechanism showed that the benzyl azides undergo protonation, nitrogen elimination, rearrangement, and electrophilic attack by the enol forms of the cyclic ketones.

Deep eutectic solvent-catalyzed Meyer-Schuster rearrangement of propargylic alcohols under mild and bench reaction conditions

The Meyer-Schuster rearrangement of propargylic alcohols into α,β-unsaturated carbonyl compounds has been revisited by setting up an atom-economic process catalyzed by a deep eutectic solvent FeCl3·6H2O/glycerol. Isomerizations take place smoothly, at room temperature, under air and with short reaction times. The unique solubilizing properties of the eutectic mixture enabled the use of a substrate concentration up to 1.0 M with the medium being recycled up to ten runs without any loss of catalytic activity.

Visible Light Photoredox-Catalyzed α-Alkylation of Cyclic Tertiary Arylamines

An efficient method was successfully developed to obtain cyclic β-amino ketones via visible-light photoredox catalysis. With this catalytic system, vinyl azides and N-Ph pyrrolidines react to form cyclic β-amino ketones by α-amino radical addition. This method provides a simple, mild, straightforward, and novel paradigm to prepare important β-amino ketones.

Gold-Catalyzed Hydroamination of Propargylic Alcohols: Controlling Divergent Catalytic Reaction Pathways To Access 1,3-Amino Alcohols, 3-Hydroxyketones, or 3-Aminoketones

A versatile approach to the valorization of propargylic alcohols is reported, enabling controlled access to three different products from the same starting materials. First, a general method for the hydroamination of propargylic alcohols with anilines is described using gold catalysis to give 3-hydroxyimines with complete regioselectivity. These 3-hydroxyimines can be reduced to give 1,3-amino alcohols with high syn selectivity. Alternatively, by using a catalytic quantity of aniline, 3-hydroxyketones can be obtained in high yield directly from propargylic alcohols. Further manipulation of the reaction conditions enables the selective formation of 3-aminoketones via a rearrangement/hydroamination pathway. The utility of the new chemistry was exemplified by the one-pot synthesis of a selection of N-arylpyrrolidines and N-arylpiperidines. A mechanism for the hydroamination has been proposed on the basis of experimental studies and density functional theory calculations.

Asymmetric synthesis of β-amino ketones by using cinchona alkaloid-based chiral phase transfer catalysts

A highly enantioselective nucleophilic addition of ketones to imines catalyzed by chiral phase-transfer catalysts (N-quaternised cinchona alkaloid ammonium salts) has been developed, and the process affords the Mannich reaction products with tertiary stereocenters in good to high yields (up to 95%) with excellent enantioselectivities (up to 97% ee).

Reductive N-alkylation of primary and secondary amines using carboxylic acids and borazane under mild conditions

An expedient strategy of reductive N-alkylation of amines with readily available carboxylic acids as alkylating reagents has been developed.