Charge-Enhanced Reactivity of Esters by a Cationic Substituent.

In this study, the high electrophilicity of carbonyl carbons attached to cationic heterocycles was observed. Triazolium-substituted esters underwent catalyst-free amidation with aliphatic amines at -50 °C and reduction with NaBH4 at -100 °C. The origin and generality of the high reactivity of these esters were systematically investigated. The findings of this work were utilized for the postmodification of N-heterocyclic carbenes, which are utilized as promising ligands in a wide range of transition-metal-catalyzed reactions.

Fluoride-Mediated Nucleophilic Aromatic Amination of Chloro-1H-1,2,3-triazolium Salts.

We report a fluoride-mediated nucleophilic aromatic amination of chloro-1H-1,2,3-triazolium salts with aliphatic amines. The reaction proceeded under mild reaction conditions to provide amino-1,2,3-triazolium salts with various functional groups, which can be utilized for further transformations. Moreover, it was found that an amino-1,2,3-triazolium salt was transformed via deprotonation into the N-heterocyclic imine (NHI), which exhibited the excellent catalytic activity for the cyanosilylation of acetophenone with trimethylsilyl cyanide.

Planar-chiral ferrocene-based triazolylidene copper complexes: synthesis, characterization, and catalysis in asymmetric borylation of α,ß-unsaturated ester.

1,2,3-Triazol-5-ylidenes have recently attracted considerable attention as versatile ligands because of their strong electron-donating properties and structural diversities. While some efforts have been devoted to the development of chiral triazolylidene-metal complexes, there is no example achieving asymmetric induction by base-metal complexes with triazolylidene ligands. Herein, we synthesized planar-chiral ferrocene-based triazolylidene copper complexes, which enabled the asymmetric borylation of methyl cinnamate with bis(pinacolato)diboron with good enantioselectivity.

Lewis acid-base synergistic catalysis of cationic halogen-bonding-donors with nucleophilic counter anions.

Cationic halogen-bonding-donors with little or non-coordinating counter anions have attracted great attention as new Lewis acid type organocatalysts. However, these anions cannot function as nucleophilic activation sites due to their low Lewis basicity. In this study, 1,3,4-triaryl-5-iodotriazolium iodides have been developed as bifunctional catalysts for simultaneous activation of nucleophiles and electrophiles. Computational and experimental studies indicated that the nucleophilicity of the counter anions plays an important role in achieving high catalytic efficiency for the cyanosilylation of aldehydes. In addition, the first report on carbon dioxide fixation by XB-donors is described.

Silver-Catalyzed Diastereo- and Enantioselective Michael Addition and 1,3-Dipolar Cycloaddition Reactions of Imino Esters to 3-Methyl-4-nitro-5-styrylisoxazoles.

The AgOAc/ThioClickFerrophos complex catalyzed conjugate additions and 1,3-dipolar cycloadditions of 3-methyl-4-nitro-5-styrylisoxazoles with 1-pyrroline-5-carboxylates and glycine imino esters to give the corresponding Michael adducts and cycloadducts, respectively, in good yields with excellent diastereo- and enantioselectivities. These reactions can provide pyrroline- or pyrrolidine-containing isoxazole hybrid molecules that have potential biological and pharmaceutical activities.

Bulky iodotriazolium tetrafluoroborates as highly active halogen-bonding-donor catalysts.

Steric bulk around catalytic centers is one of the most important factors determining catalytic reactivities and selectivities. This paper reports the synthesis of structurally diverse 5-iodo-3-methyl-1,2,3-triazolium salts and the evaluation of their catalytic activities as halogen-bonding donors for the aza-Diels-Alder reaction of 2-siloxy-1,3-butadiene with imines. We found that steric hindrance around an iodide atom in halogen-bonding donors significantly impacted catalytic efficiency.

Transition-Metal-Free Formylation of Allylzinc Reagents Leading to α-Quaternary Aldehydes.

The first example of formylation of allylzinc reagents using S-phenyl thioformate is presented. The reaction proceeded under mild conditions without any transition-metal catalyst, forming quaternary carbon centers with reactive functionalities, such as formyl and vinyl groups. Moreover, Barbier-type formylation of an allylic bromide with a sterically demanding thioformate was achieved. As a preliminary result, asymmetric formylation was conducted using a menthol-derived chiral thioformate.

Chiral triazolylidene-Pd-PEPPSI: synthesis, characterization, and application in asymmetric Suzuki-Miyaura cross-coupling.

A chiral triazolylidene-Pd-PEPPSI (PEPPSI = pyridine, enhanced, precatalyst, preparation, stabilization, initiation) complex with ferrocene-based planar chirality has been synthesized and characterized. Investigation of the electronic and steric nature of this complex revealed its powerful electron-donating ability (TEP 2044 cm-1) and high steric bulk (%Vbur = 42.2). These unique properties allow the complex to exhibit very high catalytic activity (TON = 420) for asymmetric Suzuki-Miyaura cross-coupling, providing the coupling product with good enantioselectivity (75% ee).

Metal Complex-Controlled Regio-, Diastero- and Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylides with Benzo[b]thiophene Sulfones.

The Cu(MeCN)4 PF6 /DTBM-Segphos complex catalyzed the highly diastereo- and enantioselective 1,3-dipolar cycloaddition of azomethine ylides with benzo[b]thiophene sulfones with the usual regiochemistry to give single isomers of the exo-cycloadducts in good yields. In contrast, the AgOAc/ThioClickFerrophos complex catalyzed the reaction with atypical regiochemistry to give the endo-cycloadducts as major products with excellent enantioselectivities. Thus, the choice of chiral metal complex enabled the regio- and stereoselective synthesis of chiral fused sulfolanes.

Chiral Silver Complex-Catalyzed Diastereoselective and Enantioselective Michael Addition of 1-Pyrroline-5-carboxylates to α-Enones.

A AgOAc/ThioClickFerrophos complex-catalyzed the highly diastereo- and enantioselective reaction between 1-pyrroline-5-carboxylates (1) and acyclic α-enones (2) in MeOH, in the presence of DBU, to give the single isomer Michael adducts (3) in high yields (up to 99%) with excellent enantioselectivies (up to 99% ee). Subsequent reduction of the Michael adducts with sodium cyanoborohydride successfully produced the fused pyrrolizidine ester as an almost pure single stereoisomer.

Palladium-Catalyzed Formylation of Arylzinc Reagents with S-Phenyl Thioformate.

The first example of palladium-catalyzed direct formylation of arylzinc reagents using S-phenyl thioformate is reported. The reaction proceeded under mild conditions, allowing high functional group tolerance. In addition, the developed formylation method was used to prepare deuterated and 13C-labeled aryl aldehydes from isotope-labeled S-phenyl thioformates. Moreover, this procedure was applied to an alkenylzinc halide, affording the corresponding enal.

Ligand-Controlled Stereodivergent, Enantioselective Conjugate Addition of 2-Oxazoline- and 2-Thiazoline-4-carboxylate to Nitroalkene Catalyzed by Chiral Copper Complexes.

The copper-catalyzed asymmetric conjugate addition of 2-oxazoline- and 2-thiazoline-4-carboxylate to a nitroalkene proceeded to give either the syn or anti adduct selectively in high enantiomeric excess when an appropriate chiral ligand was used. Subsequent reduction of the nitro group followed by hydrolysis of the oxazoline ring yielded an optically active γ-lactam of protected α-quaternary serine derivative.

Preparation of cycloheptane ring by nucleophilic cyclopropanation of 1,2-diketones with bis(iodozincio)methane.

The nucleophilic cyclopropanation of hexa-1,5-diene-3,4-diones with bis(iodozincio)methane afforded the Zn alkoxides of cis-dialkenylcyclopropane-1,2-diols stereoselectively. The subsequent oxy-Cope rearrangement afforded the corresponding Zn alkoxides of 5,6-dialkylcyclohepta-3,7-diene-1,3-diols.

Catalytic asymmetric aldol-type reaction of zinc enolate equivalent of amides.

Treatment of phenyl isocyanate with bis(iodozincio)methane gave a zinciomethylenated product, which acts as an amide-enoate equivalent. It did not react with an aldehyde efficiently, but gave the corresponding adduct in good yield in the presence of an aminoalcohol. Use of a catalytic amount of chiral aminoalcohol led the process to the catalytic asymmetric Aldol-type reaction.