Search

Oxidative N‐heterocyclic carbene (NHC) organocatalysis, typically leading to the formation of acyl azolium reactive intermediates, constitutes one of the most important activation strategies for the NHC‐catalyzed chemical transformations. Here, we report an unprecedented oxidative radical NHC catalysis by using peroxyester as the external single‐electron oxidant to realize divergent difunctionalization of olefins. The key to success of this chemistry is the catalytic generation of oxygen radicals that could trigger an intermolecular hydrogen atom transfer to activate the inert C−H bonds, thereby enabling the productive radical relay process. With this protocol, commonly used general chemicals could serve as radical precursors to allow efficient synthesis of value‐added products in a straightforward and cost‐effective manner. Preliminary mechanistic investigations, including control experiments and DFT calculations, shed light on the NHC organocatalytic radical reaction mechanism. [ABSTRACT FROM AUTHOR]

It has been a long-standing demand to design hetero-nanostructures for charge-flow steering in semiconductor systems. Multi-component nanocrystals exhibit multifunctional properties or synergistic performance, and are thus attractive materials for energy conversion, medical therapy, and photoelectric catalysis applications. Herein we report the design and synthesis of binary and ternary multi-node sheath hetero-nanorods in a sequential chemical transformation procedure. As verified by first-principles simulations, the conversion from type-I ZnS-CdS heterojunction into type-II ZnS-(CdS/metal) ensures well-steered collections of photo-generated electrons at the exposed ZnS nanorod stem and metal nanoparticles while holes at the CdS node sheaths, leading to substantially improved photocatalytic hydrogen-evolution performance. [ABSTRACT FROM AUTHOR]

The catalytic bis‐allylation of alkynes is an important but challenging protocol to construct all‐carbon tetra‐substituted alkenes. Particularly, the catalytic unsymmetrical bis‐allylation of alkynes remains as an underexplored task to date. We herein report an unprecedented unsymmetrical bis‐allylation by simultaneously utilizing electrophilic trifluoromethyl alkene and nucleophilic allylboronate as the allylic reagents. With the aid of robust Ni0/NHC catalysis, valuable skipped trienes can be obtained in high regio‐ and stereo‐selectivities under mild conditions. Mechanistic studies indicate that the reaction may proceed through a β‐fluorine elimination of a nickelacycle followed by a transmetalation step with allylboronate. The present method exhibits a good tolerance of various functional groups. Besides, the skipped triene products can undergo an array of elaborate transformations, which highlights the potential applications of this strategy. [ABSTRACT FROM AUTHOR]

3D covalent organic frameworks (COFs) with well‐defined porous channels are shown to be capable of inducing chiral molecular catalysts from non‐enantioselective to highly enantioselective in catalyzing organic transformations. By condensations of a tetrahedral tetraamine and two linear dialdehydes derived from enantiopure 1,1′‐binaphthol (BINOL), two chiral 3D COFs with a 9‐fold or 11‐fold interpenetrated diamondoid framework are prepared. Enhanced Brønsted acidity was observed for the chiral BINOL units that are uniformly distributed within the tubular channels compared to the non‐immobilized acids. This facilitates the Brønsted acid catalysis of cyclocondensation of aldehydes and anthranilamides to produce 2,3‐dihydroquinazolinones. DFT calculations show the COF catalyst provides preferential secondary interactions between the substrate and framework to induce enantioselectivities that are not achievable in homogeneous systems. [ABSTRACT FROM AUTHOR]

Chiral phosphoric acids are incorporated into indium‐based metal–organic frameworks (In‐MOFs) by sterically preventing them from coordination. This concept leads to the synthesis of three chiral porous 3D In‐MOFs with different network topologies constructed from three enantiopure 1,1′‐biphenol‐phosphoric acid derived tetracarboxylate linkers. More importantly, all the uncoordinated phosphoric acid groups are periodically aligned within the channels and display significantly enhanced acidity compared to the non‐immobilized acids. This facilitates the Brønsted acid catalysis of asymmetric condensation/amine addition and imine reduction. The enantioselectivities can be tuned (up to >99 % ee) by varying the substituents to achieve a nearly linear correlation with the concentrations of steric bulky groups in the MOFs. DFT calculations suggest that the framework provides a chiral confined microenvironment that dictates both selectivity and reactivity of chiral MOFs. [ABSTRACT FROM AUTHOR]