N-Heterocyclic Carbene Catalyzed [4+3] Annulation of Enals ando-Quinone Methides: Highly Enantioselective Synthesis of Benzo-ε-Lactones

Chiral N,N'-Dioxide-Scandium(III) Complex-Catalyzed Asymmetric Friedel-Crafts Alkylation Reaction of ortho-Hydroxybenzyl Alcohols with C3-Substituted N-Protected Indoles

The first Lewis acid catalyzed asymmetric Friedel-Crafts alkylation reaction of ortho-hydroxybenzyl alcohols with C3-substituted indoles is described. A chiral N,N'-dioxide Sc(OTf)₃ complex served not only to promote formation of ortho-quinone methides (o-QMs) in situ but also induced the asymmetry of the reaction. This methodology enables a novel activation of ortho-hydroxybenzyl alcohols, thus affording the desired chiral diarylindol-2-ylmethanes in up to 99 % yield and 99 % ee. A range of functional groups were also tolerated under the mild reaction conditions. Moreover, this strategy gives concise access to enantioenriched indole-fused benzoxocines.

Enantioselective Nucleophilic β-Carbon-Atom Amination of Enals: Carbene-Catalyzed Formal [3+2] Reactions

An enantioselective β-carbon amination for enals is disclosed. The nitrogen atom from a protected hydrazine with suitable electronic properties readily behaves as a nucleophile. Addition of the nitrogen nucleophile to a catalytically generated N-heterocyclic-carbene-bound α,β-unsaturated acyl azolium intermediate constructs a new carbon-nitrogen bond asymmetrically. The pyrazolidinone products from our catalytic reactions are common scaffolds in bioactive molecules, and can be easily transformed into useful compounds such as β(3) -amino-acid derivatives.

DFT perspective toward [3 + 2] annulation reaction of enals with α-ketoamides through NHC and Brønsted acid cooperative catalysis: mechanism, stereoselectivity, and role of NHC

The DFT perspective toward the [3 + 2] annulation reaction through NHC and Brønsted acid cooperative catalysis has been investigated.

NHC-Catalyzed Asymmetric Synthesis of Functionalized Succinimides from Enals and α-Ketoamides

The efficient asymmetric synthesis of highly substituted succinimides from α,β-unsaturated aldehydes and α-ketoamides via NHC-catalyzed [3+2] cycloaddition has been developed. The new scalable protocol significantly expands the utility of NHC catalysis for the synthesis of heterocycles and provides easy access to assemble a wide range of succinimides from simple starting materials.

Formal asymmetric catalytic thiolation with a bifunctional catalyst at a water-oil interface: synthesis of benzyl thiols

The enantioselective conjugated addition of tritylthiol to in situ generated ortho-quinone methides (o-QMs) is catalyzed by an acid-base bifunctional squaramide organocatalyst. The transformation proceeds with high yield (up to 99 %) and stereoselectivity (up to 97:3 e.r.) using water as solvent under mild conditions. The catalyst system provides a new strategy for the synthesis of optically active benzyl mercaptans. Control experiments suggested that o-QMs are generated by the tertiary amine moiety of the squaramide organocatalyst and that the water-oil biphase is crucial for achieving high reactivity and stereoselectivity.

An NHC-catalyzed in situ activation strategy to β-functionalize saturated carboxylic acid: an enantioselective formal [3+2] annulation for spirocyclic oxindolo-γ-butyrolactones

An in situ NHC-catalyzed activation strategy to β-functionalize saturated carboxylic acid was developed. This asymmetric formal [3+2] annulation could deliver spirocyclic oxindolo-γ-butyrolactones from saturated carboxylic acid and isatin in good yields with high to excellent enantioselectivities. The easy availability of the starting materials, direct installation of functional units at unreactive carbon atom and the convergent assembly make this protocol attractive in the field of organic synthesis.

A quantum mechanical study of the mechanism and stereoselectivity of the N-heterocyclic carbene catalyzed [4 + 2] annulation reaction of enals with azodicarboxylates

The mechanism and stereoselectivity of the NHC-catalyzed [4 + 2] annulation reaction of enals with azodicarboxylates have been investigated using the DFT method.

N-heterocyclic-carbene-catalyzed synthesis of 2-aryl indoles

A convergent and efficient transition-metal-free catalytic synthesis of 2-aryl-indoles has been developed. The interception of a highly reactive and transient aza-ortho-quinone methide by an acyl anion equivalent generated through N-hetereocyclic carbene catalysis is central to this successful strategy. High yields and a wide scope as well as the streamlined synthesis of a kinase inhibitor are reported.