Chiral Primary Amine Catalyzed Enantioselective Tandem Reactions Based on Heyns Rearrangement: Synthesis of α-Tertiary Amino Ketones

Dual Functionalization of the α,β-C-H Bonds in Alanine Ester Derivatives via Enamine-Imine Tautomerism: Construction of 4-Quinolinolate Skeletons through a Fragmentation-Reassembly Pathway

Using a SbCl3/O2 mild oxidation system, a dual functionalization of the α,β-C-H bonds in alanine ester derivatives was achieved via enamine-imine tautomerism, and a series of quinoline-4-carboxylates were synthesized through a fragmentation-reassembly pathway. The investigation of the substrate scope revealed that various functional groups were easily tolerated, highlighting that this reaction provided an efficient path for the construction of the quinoline-4-carboxylate framework.

Reversal of Reactivity of Heyns Intermediate for the Concise Synthesis of Substituted 3-Hydroxyquinolines

An efficient and general method for the synthesis of 3-hydroxyquinolines has been achieved from o-acylanilines and α-hydroxyketones in good yields. The strategy involves the intramolecular reverse trapping of the in situ generated aminoenol intermediate with an electrophilic carbonyl, viz. an interrupted Heyns rearrangement, followed by aromatization. Important features include good functional group tolerance, operational simplicity, gram-scale synthesis, and broad synthetic utility.

Regioselective Synthesis of 2,3-Disubstituted Indoles via Interrupted Heyns Rearrangement Involving C-C Bond Cleavage

A novel metal free, Brønsted acid mediated and operationally simple strategy has been developed for regioselective synthesis of 2,3-disubstituted indoles from α-hydroxyketones and o-aminoaryl ketones in excellent yields. The reaction proceeds via interrupted Heyns rearrangement through the generation of aminoenol intermediate followed by intramolecular trapping and aromatization with C-C bond cleavage and release of corresponding ester. The mechanism was further supported by the identification of ester in GCMS and reaction of cyclic α-hydroxydimethylketal, which afforded ester tethered indole derivative.

Efficient Conversion of Glucose to Hydroxymethylfurfural: One-pot Brønsted Base and Acid Promoted Selective Isomerization and Dehydration

Development of elegant, selective, and efficient strategies for the production of value-added platform chemicals from renewable feedstocks are in high demand to achieve the future needs and sustainable goals. In this context, an efficient acid-promoted synthesis of highly valuable hydroxymethylfurfural (HMF) has been demonstrated from glucose, a major constituent of lignocellulosic biomass. The major challenge in the conversion of glucose to HMF is the selective isomerization of glucose to ketose, which in the present work has been successfully addressed through the amine-mediated rearrangement of glucose to aminofructose under Amadori rearrangement. Importantly, subsequent dehydration step affords HMF and regenerates the amine employed in the first step, which could be readily recovered. In addition, scale-up and successful integration into one-pot synthesis of HMF proves the efficiency and applicability of the present transformation in large scale application. In addition, the method was also successfully extended to other monosaccharides and disaccharides to produce HMF.

The Heyns Rearrangement: Synthetic Routes Beyond Carbohydrate Chemistry

This concept review describes the recent achievements on the Heyns rearrangement appeared in literature over the last decade and aims to provide the reader with a general overview of the fundamental synthetic advances in this research area.

Enantioselective α-Amination of Amides by One-Pot Organo-/Iodine Sequential Catalysis

An one-pot organo- and iodine sequential catalysis strategy for reactions of amides with pyrazole-based primary amines was described to synthesize chiral α-amino amides with a quaternary stereocenter. This methodology exhibited strong asymmetric induction, resulting in a typical enantiomeric excess value exceeding 99% and diastereoselectivity up to >99:1 dr. Moreover, the reaction was conducted without the use of any metals or strong bases.

An interrupted Heyns rearrangement approach for the regioselective synthesis of acylindoles

An efficient and general method for the synthesis of 2- and 3-acylindoles has been achieved with high regioselectivity from o-acylanilines and α-hydroxycarbonyl or its equivalent. The strategy involves the intramolecular trapping of an in situ generated aminoenol intermediate and an interrupted Heyns rearrangement pathway, followed by aromatization or rearrangement/aromatization. Important features include excellent regiocontrol, good functional group tolerance, operational simplicity and application to gram-scale synthesis and the synthesis of an anti-tumor agent.

Catalytic asymmetric synthesis of α-tertiary aminoketones from sulfoxonium ylides bearing two aryl groups

Disclosed herein is an efficient organocatalytic formal N-H insertion reaction of arylamines with α-keto sulfoxonium ylides bearing two aryl groups, delivering a broad range of α-tertiary aminoketones with good to excellent yields and enantioselectivities (up to 90% yield and 94% ee). The utilities of this protocol were also demonstrated by facile preparation of enantioenriched 2-amino-1,2-diarylethanol bearing two different aryl groups, a type of important building block lacking efficient access.

Highly Enantioselective Brønsted Acid Catalyzed Heyns Rearrangement

Herein we report the first method for highly enantioselective Brønsted acid catalyzed Heyns rearrangements. These reactions, catalyzed by a chiral spiro phosphoric acid, afforded synthetically valuable chiral α-aryl-α-aminoketones which cannot be obtained by means of previously reported Heyns rearrangement methods. This method features low catalyst loadings, high yields and high enantioselectivities, making these reactions highly practical. We used the method to efficiently synthesize various chiral amines, including some biologically active molecules. We experimentally proved that these acid-catalyzed Heyns rearrangements proceeded via a proton-transfer process involving an enol intermediate and the stereocontrol was realized during the proton-transfer step.