Divergent reactivity of phenol- and anisole-tethered donor-acceptor α-diazoketones

The first study of the divergent reactivity of phenol/anisole-tethered donor-acceptor α-diazoketones is described. Four distinct product classes were shown to be accessible from closely related α-diazoketone precursors, with the reaction outcome dependent on the nature of the oxygen substituent on the phenol/anisole ring and the catalyst used to decompose the diazo group. Anisole and TBS-protected derivatives selectively produce three products types (cyclopropanes, tetralones and 1,2-dicarbonyls) while phenols selectively produce spirocyclic dienones.     

Divergent reactivity of allene-containing α-diazoesters using Cu and Rh catalysis

A versatile intramolecular reaction of allene-containing diazomalonates that exhibits excellent chemoselectivity for either allenic C–H insertion or cyclopropanation is demonstrated. The identity of the product depends on the transition metal catalyst that is employed for the reaction. Rh catalysts promote exclusive C–H insertion with good diastereoselectivity for the trans product, while Cu catalysis enables intramolecular cyclopropanation to yield methylenecyclopropanes with moderate to good E:Z ratios.     

Addition of indoles to oxyallyl cations for facile access to α-indole carbonyl compounds

A direct coupling of unprotected indoles and α-halo ketones via in situ generated oxyallyl cation intermediates is described. The reactions efficiently afford α-indole carbonyl compounds with good to quantitative yields.     

An organocatalyzed facile and rapid access to α-hydroxy and α-amino phosphonates under conventional/ultrasound technique

In the present work, successful implementation of ultrasound irradiation for the rapid synthesis of α-hydroxy and α-amino phosphonates under solvent-free conditions is demonstrated. Use of a novel catalyst (i.e., camphor sulfonic acid) in combination with ultrasound technique is reported for the first time. Comparative study for the synthesis of α-hydroxy and α-amino phosphonates using conventional as well as ultrasonication method is discussed.     

Efficient and facile strategy to substituted 2-aminothiazoles via ring opening of α-nitroepoxides

A novel and efficient reaction has been developed to synthesize a set of substituted 2-aminothiazoles from α-nitroepoxides and ammonium thiocyanate. This reaction could proceed smoothly at mild condition, to afford products for a wide range of substrates with good to excellent yields. A possible mechanism has also been proposed.     

Ring expansion reaction of α-sulfonyl cyclic ketones via insertion of arynes into C-C: a facile and mild access to medium- and large-sized benzannulated carbocycles

Insertion of arynes into C-C of α-sulfonyl ketones was investigated, which lead to the ring expansion reactions when α-sulfonyl cyclic ketones were used. By ring expansions and desulfonylations, medium- and large-sized benzannulated cyclic ketones were obtained in moderate yields.     

Highly regioselective control of 1,2-addition of organolithiums to α,β-unsaturated compounds promoted by lithium bromide in 2-methyltetrahydrofuran: a facile and eco-friendly access to allylic alcohols and amines

Very high regioselective 1,2-addition of organolithiums to α,β-unsaturated carbonyl-like compounds (ketones, aldehydes, and imines) in the presence of LiBr was achieved by carrying out reactions in the sustainable solvent 2-methyltetrahydrofuran. Excellent yields (in isolated product) of allylic alcohols and allylic amines were recovered under a simple experimental procedure at 0 °C.     

Construction of highly functional α-amino nitriles via a novel multicomponent tandem organocatalytic reaction: a facile access to α-methylene γ-lactams

The first tertiary amine-catalyzed multicomponent tandem Strecker-allylic-alkylation (SAA) reaction has been developed, which provides a facile access to functionalized α-amino nitriles, which could be readily converted into α-methylene-γ-butyrolactams.     

Generation and Dienophilic reactivity of α-oxoselenoaldehydes and ketones

The reaction of elemental selenium with sulfur ylides stabilized by electron-withdrawing substituent(s) affords a facile method for generation of functionalized selenocarbonyl compounds, which can be effectively trapped by Diels-Alder reaction with 1,3-dienes.     

An efficient synthesis of 2-isoxazolines from α-haloketone oximes and dimethyl sulfonium salts

2-Isoxazolines were synthesized efficiently from a formal [4+1] cycloaddition of nitrosoalkenes and sulfur ylides, which were generated in situ from α-haloketone oximes and dimethyl sulfonium salts. This approach provides a new method to synthesize a range of 2-isoxazolines in high yields and high regioselectivity.     

A simple method for the oxidation of α-amino acid esters to α-oximino esters

Magnesium bis(monoperoxyphthalate) hexahydrate (MMPP) was found to be an effective reagent for the oxidation of various α-amino acid esters to the corresponding α-oximino acid esters. This transformation could be completed under mild conditions within 2.5 h using 1.1 equiv of MMPP in THF. Clean oximino esters were obtained after quenching and extracting the reaction from sodium thiosulfate solution. The O-phosphorylated derivative of 2-oximinoglutarate exhibited slow binding inhibitory potency for the metallopeptidase prostate-specific membrane antigen (PSMA) with an IC₅₀ value of 58 nM.     

Organocatalytic asymmetric aldol reaction of hydroxyacetone with β,γ-unsaturated α-keto esters: facile access to chiral tertiary alcohols

An efficient direct asymmetric aldol reaction between hydroxyacetone and β,γ-unsaturated α-keto esters has been successfully developed. In the presence of 9-amino-9-deoxy-epi-cinchonine and trifluoroacetic acid, the direct aldol reaction of O-protected hydroxyacetone proceeded in a highly enantioselective manner, affording the desired adducts containing a chiral tertiary alcohol in high yields and with excellent enantioselectivities. The aldol products obtained are valuable precursors for the synthesis of 2-substituted glycerol derivatives.     

Gold α-oxo carbenoids in catalysis: catalytic oxygen-atom transfer to alkynes

An overview of reactive gold α-oxo carbenoid intermediates in the gold-catalyzed functionalization of alkynes is presented. Such intermediates can be generated from inter- and intramolecular oxidation of alkynes by nucleophilic oxygen-atom donor groups, such as amine N-oxides, pyridine N-oxides, nitrones, nitro compounds, sulfoxides, and epoxides. These O-atom transfer processes occur by gold-mediated addition-elimination reactions. In catalytic systems, α-oxo carbenoids can undergo nucleophilic attack by imine, arene, and migrating hydride as well as alkyl groups, leading to cascade reactions and the construction of new skeletons. The facile construction of C-E (E=C, N, S, or O) bonds makes it an attractive step-economic approach to value-added molecules from readily available starting materials. The scope, mechanisms, and reactivity of such α-oxo carbenoid species are discussed. The remarkable diversity of structures accessible is demonstrated with various recent examples.     

Covalent attachment of antagonists to the α7 nicotinic acetylcholine receptor: synthesis and reactivity of substituted maleimides

The 3-methylmaleimide congeners of the natural product methyllycaconitine (MLA) and an analogue covalently attach to functional cysteine mutants of the α7 nicotinic acetylcholine receptor (nAChR).     

One-pot synthesis of polyfunctional pyrazoles: an easy access to α-diazoketones from arylglyoxal monohydrates and tosylhydrazine

A new and efficient method for the generation of α-diazoketones has been developed from arylglyoxal monohydrates and tosylhydrazine at room temperature. 1,3-Dipolar cycloaddition reactions were used to constructing polyfunctional pyrazole derivatives by the reaction of generated α-diazoketones in situ with electron-deficient alkenes, quinones and coumarins in one pot. The one-dimensional molecular packing of 1H-benzo[f]indazole-4,9-dione derivatives along the c direction demonstrated a helical chain formation via N–H?O hydrogen-bonding.     

InX3-catalyzed haloamidation of vinyl arenes: a facile synthesis of α-bromo- and α-fluoroamides

A variety of alkenes are converted into the corresponding α-fluoroamides in high yields by selectfluor^TM in the presence of 10 mol % of InF₃ in nitrile solution. α-Bromoamides are obtained with NBS in the presence of 10 mol % InBr₃ under similar conditions. The use of Lewis acid in haloamidation significantly improved the yields and reaction rates.     

Recent progress in insertion and cyclopropanation reactions of metal carbenoids from α-diazocarbonyl compounds

Research on Chemical Intermediates - Metal–carbenoids from α-diazocarbonyl compounds are well-known reactive intermediates with a long history of useful applications in synthetic organic...