Discovery and Surprises with Cyclizations, Cycloadditions, Fragmentations, and Rearrangements in Complex Settings

Chiral sulfide and achiral sulfonic acid cocatalyzed enantioselective electrophilic tandem selenylation semipinacol rearrangement of allenols

A highly enantioselective electrophilic selenylation/semipinacol rearrangement of allenols has been developed, which is enabled by the cooperative catalysis of a chiral sulfide and an achiral sulfonic acid. The designed and synthesized chiral sulfide catalyst and selenylating reagent play a crucial role in enhancing both enantioselectivity and reactivity. This approach exhibits excellent regio-, chemo-, and enantioselectivity, providing access to diverse enantioenriched cyclopentanones featuring an arylselenovinyl-substituted quaternary carbon stereocenter. Furthermore, these products can be transformed into synthetically valuable alkyne, vinyl bromide, and aniline derivatives. Mechanistic studies reveal that the combination of a chiral sulfide and an achiral sulfonic acid not only facilitates the formation of catalytically active species, but also governs the enantioselectivity of the reaction. Meanwhile, density functional theory calculations disclose that four hydrogen bond interactions and a π‧‧‧π interaction are responsible for the observed enantioselectivity.

Synthesis of Novel Benzofuran Spiro-2-Pyrrolidine Derivatives via [3+2] Azomethine Ylide Cycloadditions and Their Antitumor Activity

A synthetic strategy of a three-component spiro-pyrrolidine compound based on benzofuran via an [3+2] azomethine ylide cycloaddition reaction is reported herein. Under mild optimal conditions, this reaction can quickly produce potentially bioactive compounds with a wide range of substrates, high yield, and simple operation. The desired products were obtained with a yield of 74-99% and a diastereomeric ratio (dr) of >20:1. Subsequently, the inhibitory effects of the compounds on the cell viability of the human cancer cell line HeLa and mouse cancer cell line CT26 were evaluated. Compounds 4b (IC50 = 15.14 ± 1.33 µM) and 4c (IC50 = 10.26 ± 0.87 µM) showed higher antiproliferative activities against HeLa cells than cisplatin (IC50 = 15.91 ± 1.09 µM); compounds 4e (IC50 = 8.31 ± 0.64 µM) and 4s (IC50 = 5.28 ± 0.72 µM) exhibited better inhibitory activities against CT26 cells than cisplatin (IC50 = 10.27 ± 0.71 µM). The introduction of electron-donating substituents was beneficial to the inhibitory activities against cancer cells. Molecular docking simulations revealed that 4e and 4s may exert corresponding bioactivities by binding to antitumor targets through hydrogen bonds, providing a new approach for discovering spiro-heterocyclic antitumor drugs.

Metal-free synthesis of gem-difluorinated heterocycles from enaminones and difluorocarbene precursors

A cascade strategy to synthesise gem-difluorinated 2H-furans from reactions of BrCF₂CO₂Et with enaminones has been described. The reactions tolerate a wide variety of functional groups under metal-free conditions. An active aminocyclopropane is proposed to be a key intermediate through the cyclopropanation of difluorocarbene with enaminones, which further triggers a regioselective C-C bond cleavage in situ to afford the corresponding gem-difluorinated 2H-furans.