Visible Light-Triggered and Catalyst- and Template-Free syn-Selective [2 + 2] Cycloaddition of Chalcones: Solid-State Suspension Reaction in Water to Access syn-Cyclobutane Diastereomers

Abstract

Light-driven [2 + 2] cycloaddition of olefins is a kind of atom-economic and green transformation for building cyclobutane scaffolds, which are widely found in bioactive compounds and natural products. Although great progress has been made in the (dia)stereoselective synthesis of anti-cyclobutanes by photocycloadditions, the selective synthesis of syn-cyclobutanes is still full of challenges. Herein, we report a visible light-triggered and catalyst- and template-free [2 + 2] cycloaddition strategy of chalcones as a solid-state reaction in water to afford syn-cyclobutanes in high yields with excellent diastereoselectivity.

Anion-Mediated Allosteric Catalysis of [2 + 2] Photocycloaddition Based on a Flexible Metallo-Amine Cage for High Diastereoselectivity

“…The unique guest-binding behaviors mediated by anions inspired us to apply this allosteric cage in photocatalytic reactions with the expectation of regulating the product selectivity. Visible-light-photosensitized olefin [2 + 2] cycloadditions have attracted extensive attention over the past decades. ,,, However, for the intermolecular coupling reactions of acyclic olefins, the syn -HH diastereomers, which are considered important in many biologically active natural products, were obtained only as a minor product in most photoreactions, which is due to the fact that the syn -HH diastereomers are thermodynamically and sterically disfavored. − Our group previously applied a cage catalyst of MOC-16, which possesses similar photoactive Ru-centers for sensitization and pockets suitable for guest dual stacking analogous with MOC-68, to achieve the syn -HH diastereoselectivity of [2 + 2] cycloaddition for acyclic olefins. , However, the rigid cage structure somewhat limits its adaptability to certain substrates for satisfactory selectivity; for example, the Chal derivatives bearing α-benzoyl functional groups generally gave poorer d.r. values as compared to those functionalized in β-position by different phenyl groups .…”

Access to Symmetrical and Unsymmetrical Cyclobutanes via Template-Directed [2+2]-Photodimerization Reactions of Cinnamic Acids

“…Such photochemical cycloaddition reactions proceed generally with very high yields and diastereoselectivities. 7 10 Moreover, this type of synthetic transformations is favored from a green chemistry perspective as they do not require the use of a solvent during the reaction. 11,12 Despite the advantages mentioned above, this approach does not provide a general solution to the selective photodimerization of any cinnamic acid derivative regardless of its solid-state structure.…”

“…Such photochemical cycloaddition reactions proceed generally with very high yields and diastereoselectivities. 7,10 Moreover, this type of synthetic transformations is favored from a green chemistry perspective as they do not require the use of a solvent during the reaction. 11,12 Despite the advantages mentioned above, this approach does not provide a general…”

Chalcone-Based Synthesis of Tetrahydropyridazines via Cloke–Wilson-Type Rearrangement-Involved Tandem Reaction between Cyclopropyl Ketones and Hydrazines

“…Moreover, chalcones are readily obtained natural products or synthetic compounds featuring a 1,3-diaryl-2-propen-1-one scaffold and have shown great potential as synthons in synthetic organic chemistry and as privileged structures in medicinal chemistry . As part of our continuing efforts on the green transformation based on chalcones, we envisioned that the corresponding cyclopropyl ketones which were readily derived from chalcones might undergo a relaying condensation and Cloke–Wilson-type rearrangement with hydrazines to generate various interesting multisubstituted tetrahydropyridazines (Scheme f). Herein, we report a facile and efficient strategy for the synthesis of tetrahydropyridazines via Cloke–Wilson-type tandem reaction between chalcone-based cyclopropyl ketones and hydrazines catalyzed by trifluoromethanesulfonic acid (TfOH) in the eco-friendly and recyclable solvent hexafluoroisopropanol (HFIP) …”