Visible-Light-Triggered Selective Intermolecular [2+2] Cycloaddition of Extended Enones: 2-Oxo-3-enoates and 2,4-Dien-1-ones with Olefins

Design, Synthesis of (±)-Millpuline A, and Biological Evaluation for the Lung Cell Protective Effects through SRC

In this study, a visible-light-induced intermolecular [2+2] photocycloaddition reaction based on flavonoids was constructed to address the problems of low yield, poor physicochemical properties, and lack of target definition in total synthesis of (±)-millpuline A whose bioactivity remains unknown. As a result, 20 derivatives were synthesized for bioactivity evaluation. Consequently, lung cell protective effects of (±)-millpuline A and compound B13 a were revealed for the first time and the crucial role of stereoconfiguration of the cyclobutane moiety in their protective effects against NNK in normal lung cells was demonstrated. Moreover, through target prediction and experimental verification in MLE-12 cells, SRC was determined to be the target of (±)-millpuline A regarding its protective effect in NNK-induced lung cell injury. Results from RT-Q-PCR and HTRF experiments verified that (±)-millpuline A could repress SRC activity through a transcriptional mechanism but not acting as an inhibitor to directly bind to and thereby inhibit SRC protein. The results in this paper are informative for the further development of visible light-catalyzed cycloaddition of flavonoids and lay a scientific foundation for understanding the bioactivity and underlying mechanism of (±)-millpuline A and other structurally similar natural skeletons.

Organophotocatalytic [2+2] Cycloaddition of Electron-Deficient Styrenes

A visible-light organophotocatalytic [2+2] cycloaddition of electron-deficient styrenes is described. Photocatalytic [2+2] cycloadditions are typically performed with electron-rich styrene derivatives or α,β-unsaturated carbonyl compounds, and with transition-metal-based catalysts. We have discovered that an organic cyanoarene photocatalyst is able to deliver high-value cyclobutane products bearing electron-deficient aryl substituents in good yields. A range of electron-deficient substituents are tolerated, and both homodimerisations and intramolecular [2+2] cycloadditions to fused bicyclic systems are available by using this methodology.

Rapid Construction of Polysubstituted “Caged” Oxa-Bishomocubane Framework from Vinylidenecyclopropanes through a Sequential Dual Catalysis of Copper(I) and Visible-Light-Induced Photosensitization

This context describes a sequential dual catalytic transformation involving copper(I)-catalyzed cyclization/isomerization/migration-dimerization and visible-light photo-induced intramolecular [2+2] cycloaddition of vinylidenecyclopropanes for the rapid construction of polysubstituted “caged” oxa-bishomocubane products. The reaction...

Coordination-driven self-assembly of anthraquinone-based metal-organic cages for photocatalytic selective [2 + 2] cycloaddition

Visible-light-promoted [2 + 2] cycloaddition provides a straightforward and efficient way to produce cyclobutanes, which are the core skeleton in commercial pharmaceuticals and fine chemicals. However, the control of the conformation to produce syn-head-to-head (syn-HH) cyclobutanes remains a grand challenge. In this work, we report the design and synthesis of anthraquinone-based metal-organic cages (MOCs) for the [2 + 2] photocycloaddition of chalcones to generate syn-HH cyclobutanes. Guided by the coordination-driven self-assembly strategy, one D2 and three D4h symmetric MOCs are constructed from anthraquinone-derived dicarboxylate linkers and 4-tert-butylsulfonylcalixarene capped tetrametallic clusters. The porous cages feature large hydrophobic cavities and photoactive anthraquinone units and are demonstrated to be efficient and recyclable photocatalysts for [2 + 2] cycloaddition of chalcones. The syn-HH diastereomers are obtained with up to 13 : 1 diastereomeric ratio (dr). The cage catalysts provide a well-defined confined space to accommodate the substrates, thus leading to enhanced selectivity relative to the free anthraquinone catalyst.

Regioselectivity and stereoselectivity of intramolecular [2 + 2] photocycloaddition catalyzed by chiral thioxanthone: a quantum chemical study

Chiral photosensitizer-catalyzed stereoselective olefin cyclization has shown its significance in organic synthesis.