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]

Fluorinated ketones are widely prevalent in numerous biologically interesting molecules, and the development of novel transformations to access these structures is an important task in organic synthesis. Herein, we report the multicomponent radical acylfluoroalkylation of a variety of olefins in the presence of various commercially available aromatic aldehydes and fluoroalkyl reagents through N‐heterocyclic carbene organocatalysis. With this protocol, over 120 examples of functionalized ketones with diverse fluorine substituents have been synthesized in up to 99 % yield with complete regioselectivity. The generality of this catalytic strategy was further highlighted by its successful application in the late‐stage functionalization of pharmaceutical skeletons. Excellent diastereoselectivity could be achieved in the reactions forging multiple stereocenters. In addition, preliminary results have been achieved on the catalytic asymmetric variant of the olefin difunctionalization process. [ABSTRACT FROM AUTHOR]

Two chiral carboxylic acid functionalized micro- and mesoporous metal-organic frameworks (MOFs) are constructed by the stepwise assembly of triple-stranded heptametallic helicates with six carboxylic acid groups. The mesoporous MOF with permanent porosity functions as a host for encapsulation of an enantiopure organic amine catalyst by combining carboxylic acids and chiral amines in situ through acid-base interactions. The organocatalyst-loaded framework is shown to be an efficient and recyclable heterogeneous catalyst for the asymmetric direct aldol reactions with significantly enhanced stereoselectivity in relative to the homogeneous organocatalyst. [ABSTRACT FROM AUTHOR]

Innentitelbild: Radical Acylfluoroalkylation of Olefins through N-Heterocyclic Carbene Organocatalysis (Angew. B Die Mehrkomponenten-Acylfluoralkylierung b von Olefinen durch NHC-Organokatalyse (NHC=N-heterocyclisches Carben) wird im Forschungartikel von J.-L. Li, B. Han, Q.-Z. Die Allgemeingültigkeit der Methode wird durch die Modifizierung pharmazeutischer Gerüste in späten Synthesestadien unterstrichen. [Extracted from the article]

The direct functionalization of inert C(sp3)−H bonds under environmentally benign catalytic conditions remains a challenging task in synthetic chemistry. Here, we report an organocatalytic remote C(sp3)−H acylation of amides and cascade cyclization through a radical‐mediated 1,5‐hydrogen atom transfer mechanism using N‐heterocyclic carbene as the catalyst. Notably, a diversity of nitrogen‐containing substrates, including simple linear aliphatic carbamates and ortho‐alkyl benzamides, can be successfully applied to this organocatalytic system. With the established protocol, over 120 examples of functionalized δ‐amino ketones and isoquinolinones with diverse substituents were easily synthesized in up to 99 % yield under mild conditions. The robustness and generality of the organocatalytic strategy were further highlighted by the successful acylation of unactivated C(sp3)−H bonds and late‐stage modification of pharmaceutical molecules. Then, the asymmetric control of the radical reaction was attempted and proven feasible by using a newly designed chiral thiazolium catalyst, and moderate enantioselectivity was obtained at the current stage. Preliminary mechanistic investigations including several control reactions, KIE experiments, and computational studies shed light on the organocatalytic radical reaction mechanism. [ABSTRACT FROM AUTHOR]

Titelbild: Remote C(sp3)-H Acylation of Amides and Cascade Cyclization via N-Heterocyclic Carbene Organocatalysis (Angew. Cyclization Reactions, C-H Functionalization, Isoquinolinone, NHC Organocatalysis, Radical Acylation Keywords: Cyclization Reactions; C-H Functionalization; Isoquinolinone; NHC Organocatalysis; Radical Acylation EN Cyclization Reactions C-H Functionalization Isoquinolinone NHC Organocatalysis Radical Acylation 1 1 1 03/30/22 20220404 NES 220404 B Eine organokatalytische b C(sp SP 3 sp )-H-Acylierung von Amiden wurde auf der Grundlage einer 1,5-Wasserstoffatom-Transferstrategie entwickelt. [Extracted from the article]