Shaoxia Lin

One-Pot Cascade Leading to Direct α-Imidation of Ketones by a Combination of N-Bromosuccinimide and 1,8-Diazabicyclo[5.4.1]undec-7-ene

A one-pot cascade transformation of ketones into α-imidoketones has been developed, in which N-bromosuccinimide (NBS) provides both electrophilic bromine and nucleophilic nitrogen sources, and diazabicyclo[5.4.1]undec-7-ene (DBU) functions as a base and a nucleophilic promoter for the activation of NBS. α-Bromination is supposed as the key step in the process, which takes place between more electrophilic bromide active species and enolates.

N-bromosuccinimide/1,8-diazabicyclo[5.4.1]undec-7-ene combination: β-amination of chalcones via a tandem bromoamination/debromination sequence.

A one-pot cascade transformation of chalcones into β-imidoketones has been developed, in which NBS provides both electrophilic bromine and nucleophilic nitrogen sources, and DBU functions as a nucleophilic reagent to activate NBS to be a more electrophilic bromine species and to further remove the bromine of α-bromoketones. The whole process involves tandem bromoamination and debromination, which represents a unique example of preparing β-aminoketones by the reaction of chalcones with the NBS/DBU combination.

Acetoacetanilides as Masked Isocyanates: Facile and Efficient Synthesis of Unsymmetrically Substituted Ureas

A general and practical method for the preparation of unsymmetrically substituted ureas has been developed. By the reactions of acetoacetanilides with various amines including primary/secondary amines, a series of substituted aryl ureas were achieved in high yields. Acetoacetanilide substrates can be considered as masked reagents that liberate reactive isocyanates in situ.

Halonium-initiated C-O bond formation via umpolung of α-carbon to the carbonyl: efficient access to 5-amino-3(2H)-furanones.

Highly efficient C-O bond formation has been developed via carboxylic acid catalyzed reaction of 1-acetylcyclopropanecarboxamides with N-halosuccinimide (NXS), which provides strategically novel and atom-economic access to biologically important 5-amino-3(2H)-furanones. The mechanism of halonium-initiated tandem oxa-cyclization and ring opening of cyclopropane was proposed. A variety of nucleophiles were found to open the cyclopropane.

Iron(II)-catalyzed oxidation of sp3 C-H bonds adjacent to a nitrogen atom of unprotected arylureas with tert-butyl hydroperoxide in water.

With a FeSO(4)/TBHP system in water, direct oxidation of sp(3) C-H bonds adjacent to nitrogen of arylureas to give both unprecedented tert-butoxylated and hydroxylated products 2 was revealed. Under elevated temperatures, either 2-oxo-N-arylpyrrolidine-1-carboxamides 3 or 1,3-diarylureas 4 were attained, depending on the aliphatic ring size of the arylurea substrates.

Aza-oxy-carbanion relay via non-Brook rearrangement: efficient synthesis of furo[3,2-c]pyridinones.

An aza-oxy-carbanion relay via tandem Michael addition/ring opening of cyclopropane and recyclization/carbanion migration/electrophile trapping has been developed by the utilization of 1-cinnamoylcyclopropanecarboxamides to react with various electrophiles. This represents the first example of anion relay chemistry via non-Brook rearrangement. This novel protocol has been applied in the facile and efficient synthesis of biologically active bicyclic furo[3,2-c]pyridinone compounds.

Halonium-initiated electrophilic cascades of 1-alkenoylcyclopropane carboxamides: efficient access to dihydrofuropyridinones and 3(2H)-furanones

Halonium-initiated cascade reaction of 1-alkenoylcyclopropane carboxamides was developed, which leads to the production of dihydrofuropyridinones and 3(2H)-furanones, respectively, depending on the property of substituents on the enone moiety.

N-Bromosuccinimide-carboxylic acid combination: mild and efficient access to dibromination of unsaturated carbonyl compounds

A mild, efficient and practical method for the preparation of dihalogenated products has been developed. Benzoic acid (0.2 equiv.) is capable of catalyzing the reactions of unsaturated carbonyl compounds with N-halosuccinimides (NXS, X = Br and Cl) to afford a series of dihalogenated products at room temperature.

Organocatalyzed Anion Relay Leading to Functionalized 2,3-Dihydrofurans

A DABCO-mediated organocatalyzed anion relay cascade based on 1-cinnamoylcyclopropanecarboxamides has been developed and applied in the construction of 2,3-dihydrofurans with the original alkene and amide functionalities intact. In the aza-oxy-carbanion relay process, DABCO provides both the electron source and sink. The enolate anion-triggered ring opening of the cyclopropane is ascribed to the key step in the anion relay cascade.

Otherwise inert reaction of sulfonamides/carboxamides with formamides via proton transfer-enhanced reactivity

NBS-mediated addition-elimination reaction of sulfonamides/carboxamides and formamides afforded N-sulfonylamidines and N-formylarylamides, respectively, depending on the different mechanism of elimination. Hydrogen bond-induced proton transfer leads to enhanced reactivities and was proposed as the key driving force for the reaction to take place. The protocol demonstrates the possibility of constructing chemical bonds based on a proton transfer strategy induced by noncovalent hydrogen bond interaction.