Xingxing Wu

Nickel(II)-catalyzed diastereoselective [3+2] cycloaddition of N-tosyl-aziridines and aldehydes via selective carbon-carbon bond cleavage.

An efficient and mild Ni(ClO(4))(2)-catalyzed [3+2] cycloaddition of N-tosylaziridines and aldehydes via C-C bond cleavage was developed. The cycloaddition reaction proceeds with high diastereoselectivity and regioselectivity leading to highly substituted 1,3-oxazolidines. Notably, this novel reaction can be easily expanded to gram level scale and the thermal conditions cannot achieve the same transformation.

N‑Heterocyclic Carbene-Catalyzed Radical Reactions for Highly Enantioselective β‑Hydroxylation of Enals

An N-heterocyclic carbene-catalyzed β-hydroxylation of enals is developed. The reaction goes through a pathway involving multiple radical intermediates, as supported by experimental observations. This oxidative single-electron-transfer reaction allows for highly enantioselective access to β-hydroxyl esters that are widely found in natural products and bioactive molecules.

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.

Construction of Fused Pyrrolidines and β‐Lactones by Carbene‐Catalyzed C−N, C−C, and C−O Bond Formations

A carbene-catalyzed intermolecular C-N bond formation, which initiates a highly selective cascade reaction for the synthesis of pyrrolidine fused β-lactones, is disclosed. The nitrogen-containing bicyclic β-lactone products are obtained with good yields and excellent stereoselectivities. Synthetic transformations of the reaction products into useful functional molecules, such as amino catalysts, can be efficiently realized under mild reaction conditions. Mechanistically, this study provides insights into modulating the reactivities of heteroatoms, such as nitrogen atoms, in challenging carbene-catalyzed asymmetric carbon-heteroatom bond-forming reactions.

Rapid access to bicyclic δ-lactones via carbene-catalyzed activation and cascade reaction of unsaturated carboxylic esters

Carboxylic esters are an excellent choice of substrates in organic synthesis. Here we demonstrate that carbene-catalyzed activation of α,β-unsaturated ester can be developed to synthesize sophisticated multi-cyclic molecules in a single step cascade process. The iridoid-type lactone products are obtained with high stereo-selectivities, and can readily undergo further transformations.

Sulfoxidation of alkenes and alkynes with NFSI as a radical initiator and selective oxidant

Sulfoxides are important functional molecules. We develop a short-route (one-pot) synthesis of this class of molecules by reacting thiols with alkenes or alkynes under mild and metal-free conditions. N-Fluorobenzenesulfonimide (NFSI) is used to play dual roles: as a radical initiator for a thiol-ene/-yne reaction to form sulfide adducts, and as efficient oxidant for conversion of the sulfides formed in situ to sulfoxides. Over-oxidation of the sulfoxides to sulfones is avoided in our approach.

Polyhalides as Efficient and Mild Oxidants for Oxidative Carbene Organocatalysis by Radical Processes

Simple and inexpensive polyhalides (CCl4 and C2 Cl6 ) have been found to be effective and versatile oxidants in removing electrons from Breslow intermediates under N-heterocyclic carbene (NHC) catalysis. This oxidative reaction involves multiple single-electron-transfer (SET) processes and several radical intermediates. The α, β, and γ-carbon atoms of aldehydes and enals could be readily functionalized. Given the low cost of the oxidants and the broad applicability of the reactions, this study is expected to greatly enhance the feasibility of oxidative NHC catalysis for large-scale applications. Also this new SET radical process with polyhalides as single-electron oxidants will open a new avenue in the development of NHC-catalyzed radical reactions.

Carbene-Catalyzed Reductive Coupling of Nitrobenzyl Bromide and Nitroalkene via the Single-Electron-Transfer (SET) Process and Formal 1,4-Addition

A carbene-catalyzed reductive 1,4-addition of nitrobenzyl bromides to nitroalkenes is disclosed. The reaction proceeds via a carbene-enabled single-electron-transfer process that generates radicals as key intermediates. The present study expands the potentials of carbene catalysis and offers unusual transformations for common substrates in organic synthesis.

Trimerization of enones under air enabled by NHC/NaOtBu via a SET radical pathway

An unusual trimerization of enone via a formal [2 + 2 + 2] process is disclosed. The reaction is initiated by a radical process enabled by NaOtBu and N-heterocyclic carbene (NHC). Molecular oxygen (air) is involved in key steps of the radical intermediate formation and carbon–carbon bond cleavage in this trimerization reaction to form highly substituted cyclohexane derivatives. In previous studies, alkali metal tert-butoxides such as NaOtBu were mainly employed to generate radical intermediates from aryl halides. Here we provide a new avenue in using NaOtBu and combined NHC/NaOtBu to generate radical intermediates from enones for further reactions.