Recent Advances in the Construction of Bridged Rings through Cycloadditions and Cascade Reactions

Asymmetric Synthesis of Bridged N-Heterocycles with Tertiary Carbon Center through Barbas Dienamine-Catalysis: Scope and Applications

A direct aza-Diels-Alder reaction between 2-aryl-3H-indolin-3-ones and cyclic-enones has been developed to access chiral indolin-3-one fused polycyclic bridged compounds. This method proceeds via proline-catalyzed Barbas-dienamine intermediate formation from various cyclic-enones such as 2-cyclopenten-1-one, 2-cyclohexene-1-one, and 2-cycloheptene-1-one, followed by a reaction with 2-aryl-3H-indol-3-ones. Several indolin-3-ones fusing [2.2.2], [2.2.1], and [3.2.1] skeletons decorated with a tertiary carbon chiral center have been prepared. Computational studies (DFT) supported the observed stereoselectivity in the method. The synthesized compounds have shown exciting photophysical activities and selective sensing of Pd²⁺ and Fe³⁺ ions through the fluorescence quenching "switch-off" mode.

Construction of bridged polycycles through dearomatization strategies

Bridged polycycles are privileged molecular skeletons with wide occurrence in bioactive natural products and pharmaceuticals. Therefore, they have been the pursing target molecules of numerous chemists. The rapid and convenient generation of sp3-rich complex three-dimensional molecular skeletons from simple and easily available aromatics has made dearomatization a highly valuable synthetic tool for the construction of rigid and challenging bridged rings. This review summarizes the-state-of-the-art advances of dearomatization strategies in the application of bridged ring formation, discusses their advantages and limitations and the in-depth mechanism, and highlights their synthetic value in the total synthesis of natural products. We wish this review will provide an important reference for medicinal and synthetic chemists and will inspire further development in this intriguing research area.

Catalytic asymmetric dearomative [4 + 2] annulation of 2-nitrobenzofurans and 5H-thiazol-4-ones: stereoselective construction of dihydrobenzofuran-bridged polycyclic skeletons

An organocatalytic asymmetric dearomative [4 + 2] annulation of 2-nitrobenzofurans and 5H-thiazol-4-ones is developed for the construction of dihydrobenzofuran-bridged polycyclic skeletons with good results.

Diastereoselective construction of cage-like and bridged azaheterocycles through dearomative maximization of the reactive sites of azaarenes

A highly diastereoselective multicomponent dearomative multifunctionalization of N-alkyl activated azaarenes with 1,5-diazapentadienium salts has been developed to access structurally rigid and synthetically challenging cage-like and bridged azaheterocycles.

Copper(i)-catalyzed [4 + 2] cycloaddition of aza-ortho-quinone methides with bicyclic alkenes

An efficient copper(i)-catalyzed [4 + 2] cycloaddition of aza-ortho-quinone methides (ao-QMs) and bicyclic alkenes to prepare tetrahydroquinoline-fused bicycles bearing multiple stereocenters in good yields is reported.