Enantioselective intermolecular[2+2]photocycloadditions of vinylazaarenes with triplet-state electron-deficient olefins

The development of catalytic asymmetric radical reactions is an attractive but formidable task.The high reactivity of radicals enables the use of readily accessible feedstocks and mild reaction conditions,but it leads to substantial difficulty for chiral catalysts to provide sufficient enantiocontrol.Moreover,a racemic background process is often inevitable,further deteriorating enantioselectivity.In this regard,an effective protocol has been established for enantioselective intermolecular[2+2]photocycloadditions to overcome the challenges,which is capitalising on the ground-state preassociations of chiral catalysts with photoactivated substrates.Here,we report the viability of substrate-differentiating synergistic catalysis for this important reaction.In this new platform,energy transfer occurs between DPZ as a photosensitizer and enones or(E)-2-substituted vinylazaarenes for producing triplet-state species,and chiral phosphoric acid interacts with ground-state 2-vinylazaarenes via hydrogen bonding for subsequent enantiofacial cycloaddition.Although all active species are dispersed in the reaction system,valuable enantioenriched mono-and di-azaarene-functionalized cyclobutanes are obtained efficiently and selectively.In addition to constructing all-carbon quaternary stereocentres,flexible modulation of azaaryl groups and other substituents on the cyclobutane ring is also operative.

Direct enantioselective reduction of C=C bond of β-polyfluoro-alkylated enones via asymmetric photoredox catalysis

Direct enantioselective reduction of the C=C bond ofβ-polyfluoro-alkylated enones is an important but long-pending subject in asymmetric catalysis.Here,we report on the viability of visible light-driven cooperative photoredox and chiral hydrogenbonding catalysis to effectively address this challenge,as a variety of products are obtained in high yields(up to 85%)with good to excellent enantioselectivities(up to 98%ee).The formation of thermodynamically favorable enol intermediates after double single-electron reduction represents the center of the success.Additionally,the utility of the current method is validated by the convenient regio-specific and-diverse synthesis of various deuterated derivatives for these products using inexpensive D_(2)O as the deuterium source.

Recent applications of macrocycles in supramolecular catalysis

Numerous supramolecular macrocycles have been utilized for developing catalysts by exploiting their specific molecular recognition and ability to form inclusion complexes through noncovalent interactions. The cyclic structure and modified functional groups of these macrocycles can influence substrate and transition state stability, as well as reaction selectivity. The inner cavities of these macrocycles are particularly beneficial, as they enable substrates to adopt preorganized arrangements and serve as versatile platforms for highly efficient supramolecular catalytic systems. This minireview provides an overview of recent advancements in supramolecular catalysis using various macrocycles, such as crown ethers, cyclodextrins,calixarenes, pillararenes, cucurbiturils, and other novel macrocycles.

Strategies for constructing seven-membered rings:Applications in natural product synthesis

The seven-membered ring motifs are found in bioactive pharmaceuticals and a wide range of natural products,including alkaloids and terpenoids,which hold significant importance in synthetic chemistry and has garnered considerable attention from both academia and industry.Despite the challenges faced in the past decade,the total synthesis of natural products incorporating the non-aromatic cycloheptane skeletons remains a compelling pursuit.Recently,numerous elegant strategies for constructing the sevenmembered ring system have been successfully developed.This review focuses on the recent advancements in this field from 2017 to April 2023,highlighting key transformations utilized to construct the non-aromatic cycloheptane core structures and serves as a valuable guide for synthetic chemists engaged in the total synthesis of natural products containing seven-membered ring motifs.