Bi(OAc)3/Chiral Phosphoric Acid-Catalyzed Enantioselective 1,2- and Formal 1,4-Allylation Reaction of β,γ-Unsaturated α-Ketoesters

Catalyst-controlled regiodivergence and stereodivergence in formal cross-[4+2] cycloadditions: The unique effect of bismuth(III)

The [4+2] cycloaddition is crucial for constructing six-membered rings in pharmaceuticals and natural products. Cross-[4+2] cycloadditions offer greater product diversity than traditional diene-dienophile reactions due to multiple possible pathways. However, precise control over regio- and stereoselectivity for various isomers remains a great challenge. This study reports catalyst-controlled regiodivergent formal cross-cycloadditions of acyclic dienes and enones, significantly enhancing access to diverse pyrazole-fused spirooxindoles. Chiral phosphoric acid (CPA) catalysis enables endoselective [4+2] cycloadditions, while Bi(III) with a CPA ligand yields [2+4] products with high regio- and stereoselectivity. A Claisen rearrangement of the [2+4] adduct produces the exo-selective [4+2] product, further increasing stereochemical diversity and enabling the synthesis of six regio- and stereo-isomers from a single substrate set. DFT calculations reveal that Bi(III) reverses regioselectivity by repositioning reactants in the CPA pocket and stabilizing the enone oxygen's negative charge. In addition, product 3as demonstrates therapeutic potential against triple-negative breast cancer, with an IC50 of 8.5 μM in MDA-MB-453 cells.

Recent Advances in Asymmetric Catalysis Using p-Block Elements

The development of new methods for enantioselective reactions that generate stereogenic centres within molecules are a cornerstone of organic synthesis. Typically, metal catalysts bearing chiral ligands as well as chiral organocatalysts have been employed for the enantioselective synthesis of organic compounds. In this review, we highlight the recent advances in main group catalysis for enantioselective reactions using the p-block elements (boron, aluminium, phosphorus, bismuth) as a complementary and sustainable approach to generate chiral molecules. Several of these catalysts benefit in terms of high abundance, low toxicity, high selectivity, and excellent reactivity. This minireview summarises the utilisation of chiral p-block element catalysts for asymmetric reactions to generate value-added compounds.

Enantioselective N-Heterocyclic Carbene Catalyzed α-Oxidative Coupling of Enals with Carboxylic Acids Using an Iodine(III) Reagent

The enantioselective α-oxidative coupling of enals with carboxylic acids was developed via the umpolung of an NHC-bound enolate with an iodine(III) reagent. The corresponding α-acyloxyl-β,γ-unsaturated esters were afforded in good yields, with high regio- and enantioselectivities. The key step of the reaction involves the formation of enol iodine(III) intermediate from the enolate with iodosobenzene, which changes the polarity of α-carbon of the enal from nucleophilic to electrophilic, and thus facilitates the subsequent addition of carboxylate.