Bifunctional Squaramide‐Catalysed Asymmetric Michael/Hemiketalization/Retro‐Aldol Reaction of Unsaturated Thiazolones with α‐Nitroketones: Synthesis of Chiral 4‐Acyloxythiazole Derivatives

Squaramide-Catalyzed Asymmetric Mannich/Hemiketalization Retro-Henry Cascade Reaction of o-Hydroxy-α-Aminosulfones with α-Nitroketones

A concise and efficient asymmetric Mannich/hemiketalization/retro-Henry cascade reaction between o-hydroxy-α-aminosulfones and α-nitroketones was developed by utilizing a cinchona-derived bifunctional squaramide catalyst. This methodology provided access to β-nitro-substituted amino compounds with up to 95% yield and >99% ee. The practicality was demonstrated by scale-up and diverse derivatizations, including the synthesis of imidazolidinone and amino acid analogs. This is the first report of α-nitroketones in such a cascade reaction, offering a valuable approach for the synthesis of chiral β-nitro amino compounds.

Zinc-Catalyzed Asymmetric Cascade Michael/Acyl Transfer Reaction between α-Hydroxy Aryl Ketones and Enynones

We described herein a neoteric enantioselective cascade Michael/acyl transfer reaction of enynones and α-hydroxy aryl ketones catalyzed by dinuclear zinc cooperative catalysis. A series of structurally diverse chiral 1,5-dicarbonyl compounds were synthesized in good yields with excellent stereoselectivities. This strategy features broad substrate scope, high atom economy, as well as enynones as efficient electrophilic acyl transfer reagents in asymmetric cascade reactions for the first time.

Recent Advances in Greener Asymmetric Organocatalysis Using Bio-Based Solvents

Efficient synthetic methods that avoid the extensive use of hazardous reagents and solvents, as well as harsh reaction conditions, have become paramount in the field of organic synthesis. Organocatalysis is notably one of the best tools in building chemical bonds between carbons and carbon-heteroatoms; however, most examples still employ toxic volatile organic solvents. Although a portfolio of greener solvents is now commercially available, only ethyl alcohol, ethyl acetate, 2-methyltetrahydrofuran, supercritical carbon dioxide, ethyl lactate, and diethyl carbonate have been explored with chiral organocatalysts. In this review, the application of these bio-based solvents in asymmetric organocatalytic methods reported in the last decade is discussed, highlighting the proposed mechanism pathway for the transformations.

A squaramide-catalysed asymmetric cascade Michael addition/acyl transfer reaction between unsaturated benzothiophenones and α-nitroketones

An efficient and practical organocatalytic asymmetric strategy was developed using unsaturated benzothiophenones and α-nitroketones catalysed by bifunctional squaramide via Michael addition and acyl transfer steps. A broad range of chiral acyloxybenzothiophene derivatives were obtained in good yields (up to 97%) with excellent enantioselectivities (up to 98% ee). What's more, employing different chiral squaramide catalysts and unsaturated benzothiophenones can deliver the acyloxy unit at the 2-position or 3-position of benzothiophene.

Organocatalytic Asymmetric Cascade Michael-acyl Transfer Reaction between 2-Fluoro-1,3-diketones and Unsaturated Thiazolones: Access to Fluorinated 4-Acyloxy Thiazoles

Quinine derived bifunctional urea catalyzed cascade Michael-acyl transfer reaction of 5-alkenyl thiazolones and monofluorinated β-diketones has been developed. The fluorine containing 4-acyloxy thiazoles were synthesized in high yields and good diastereo-and excellent enantioselectivities. Synthetic transformations, including synthesis of 4-hydroxy thiazoles, have been demonstrated.

Organocatalytic asymmetric Michael/acyl transfer reaction between α-nitroketones and 4-arylidenepyrrolidine-2,3-diones

An organocatalytic asymmetric Michael/acyl transfer reaction between α-nitroketones and 4-arylidenepyrrolidine-2,3-diones is reported. A bifunctional thiourea catalyst was found to be effective for this reaction. With 10 mol % of the catalyst, good results were attained for a variety of 1,5-dihydro-2H-pyrrol-2-ones under mild reaction conditions.

Recent advances in the catalytic asymmetric reactions of thiazolone derivatives

Thiazolones as a class of five-membered heterocyclic compounds containing both nitrogen and sulfur, have been proved to possess important biological activities. Because thiazolone molecules have many reaction sites, they can carry out a series of modification reactions, which makes them good reaction substrates for various molecular syntheses. In recent years, research on the use of asymmetric organocatalysis to construct thiazolone derivatives has attracted a lot of attention. Among these, some breakthrough results have been achieved in the asymmetric synthesis of thiazolone derivatives. This review highlights recent developments in thiazolone derivatives in asymmetric reactions, including Michael additions, Mannich reactions as well as various cascade reactions.