DBU-Mediated Construction of 1,3,5-Trisubstituted Benzenes via Annulation of α,β-Unsaturated Carboxylic Acids and α-Cyano-β-methylenones

An overview of the synthetic strategies of C3-symmetric polymeric materials containing benzene and triazine cores and their biomedical applications

C3-symmetric star-shaped materials are an emerging category of porous organic polymers with distinctive properties such as permanent porosity, good thermal and chemical stability, high surface area, and appropriate functionalization that promote outstanding potential in various applications. This review is mostly about constructing benzene or s-triazine rings as the center of C3-symmetric molecules and using side-arm reactions to add functions to these molecules. Over and above this, the performance of various polymerization processes has been additionally investigated in detail, including the trimerization of alkynes or aromatic nitriles, polycondensation of monomers with specific functional groups, and cross-coupling building blocks with benzene or triazine cores. Finally, the most recent progress in biomedical applications for C3-symmetric materials based on benzene or s-triazine have been summarized.

DBU-Mediated Isomerization/6-π Electro-Cyclization/Oxidation Cascade of Sulfonyl-Substituted Allenyl Ketones for the Construction of Hetero-1,3,5-Trisubstituted Benzene

1,3,5-tri-substituted benzene rings emerged with unique properties has widespread applications in materials, boosting the rapid development of their synthesis. Despite the significance, the direct construction of hetero-1,3,5-trisubstituted benzene core was far less-developed. Herein, we realized a DBU-mediated isomerization/6-π electro-cyclization/oxidative aromatization cascade of sulfonyl-substituted allenyl ketones under an air atmosphere (DBU=1,8-diazabicyclo[5.4.0]undec-7-ene). This versatile protocol featured metal-free conditions, easy operation, and broad functional group tolerance provides a new avenue for the construction of hetero-1,3,5-tri-substituted benzene.

Assembly of unsymmetrical 1,3,5-triarylbenzenes via tandem reaction of β-arylethenesulfonyl fluorides and α-cyano-β-methylenones

A transition-metal-free tandem reaction of β-arylethenesulfonyl fluorides and α-cyano-β-methylenones has been revealed. In the presence of cesium carbonate, 2-arylethenesulfonyl fluorides react with α-cyano-β-methylenones through a tandem Diels-Alder cycloaddition/sulfur (VI) fluoride...

Enantioselective Synthesis of Axially Chiral Benzothiophene/Benzofuran-Fused Biaryls by N-Heterocyclic Carbene Catalyzed Arene Formation

Axially chiral biaryl scaffolds are prevalent in natural products, chiral ligands, and organocatalysts. However, N-heterocyclic carbene (NHC) catalyzed de novo construction of an aromatic ring with concomitant axial chirality induction for the synthesis of biaryl atropisomers is far less developed, and the efficient synthesis of axially chiral tetra-ortho-substituted biaryls remains an unsolved problem under NHC catalysis. Reported here is an NHC-catalyzed de novo synthesis of axially chiral benzothiophene/benzofuran-fused biaryls from enals and 2-benzyl-benzothiophene/benzofuran-3-carbaldehydes through a [2+4] annulation, decarboxylation, and oxidative aromatization cascade with central-to-axial chirality conversion. The developed method provides efficient and general access to novel axially chiral benzothiophene/benzofuran-fused biaryls in high enantioselectivities and works well for the synthesis of tetra-ortho-substituted biaryls.

α,β-Unsaturated acyl ammonium species as reactive intermediates in organocatalysis: an update

α,β-Unsaturated acyl ammonium species are versatile intermediates that have been applied in a variety of transformations including Michael additions, domino reactions and cycloadditions. Many of these transformations are promoted by chiral Lewis base catalysts, enabling the rapid generation of molecular complexity with high stereochemical control. This review highlights recent developments in the generation and application of α,β-unsaturated acyl ammonium intermediates reported since a previous review of this area in 2016. Particular emphasis will be placed on reports providing mechanistic insight into catalytic transformations and observed selectivities. A perspective on current challenges and potential future developments in the field of α,β-unsaturated acyl ammonium catalysis is also provided.

Substrate-directed chemo- and regioselective synthesis of polyfunctionalized trifluoromethylarenes via organocatalytic benzannulation

Highly chemo- and regioselective substrate-directed benzannulation of trisubstituted CF₃-alkenes and 2-benzylidenemalononitriles or 2-nitroallylic acetates has been achieved via Michael-initiated [4 + 2] or Rauhut–Currier-initiated [3 + 3] annulation.

Organocatalyzed ring-opening polymerization (ROP) of functional β-lactones: new insights into the ROP mechanism and poly(hydroxyalkanoate)s (PHAs) macromolecular structure

The organocatalyzed ROP of some 4-alkoxymethylene-β-propiolactones (BPL^ORs) towards the formation of the corresponding poly(hydroxyalkanoate)s (PHAs; PBPL^ORs) is investigated simply using basic organocatalysts of the guanidine (TBD), amidine (DBU) or phosphazene (BEMP) type.

Direct access to multi-functionalized benzenes via [4 + 2] annulation of α-cyano-β-methylenones and α,β-unsaturated aldehydes

An efficient [4 + 2] benzannulation of α-cyano-β-methylenones and α,β-unsaturated aldehydes was achieved under metal-free reaction conditions selectively delivering a wide range of polyfunctional benzenes in high yields respectively (up to 94% yield).

An efficient [4 + 2] benzannulation of α-cyano-β-methylenones and α,β-unsaturated aldehydes was achieved under metal-free reaction conditions selectively delivering a wide range of polyfunctional benzenes in high yields respectively (up to 94% yield).

Amine-catalyzed and functional group-controlled chemo- and regioselective synthesis of multi-functionalized CF3-benzene via a metal-free process

A novel strategy for the synthesis of CF₃-containing multi-substituted benzenes with high chemo- and regioselectivities under metal-free and air-tolerant conditions was established.