Totally found 1039 items.

  • [期刊] Water Phase, Room Temperature, Ligand-Free Suzuki-Miyaura Cross-Coupling: A Green Gateway to Aryl Ketones by C-N Bond Cleavage
    We report herein a green strategy for synthesis of aryl ketones from twisted amides by using Pd(OAc)(2) as catalysts. This method shows high functional group tolerance to offer a variety of ketones in good yields under mild conditions (up to 94 %). Notably, this methodology demonstrates the first water phase, room temperature, ligand-free Suzuki-Miyaura coupling through C-N bond cleavage, which is environmentally friendly and might facilitate the development of amide based green chemistry.
  • [期刊] Benzyl C–O and C–N Bond Construction via C–C Bond Dissociation of Oxime Ester under Visible Light Irradiation

    A photoredox benzyl activation was developed via formidable C(sp 3 )–C(sp 3 ) bond dissociation of 1‐aryl acetone oxime esters, which were easily prepared from benzyl ketones. Further coupling with O‐ and N‐ nucleophiles successfully forged important benzyl ether and amines derivatives in one pot. In this process, different substitutions on oxime esters were found compatible and various primary and secondary alcohols and amines, as well as amides showed good performance as nucleophiles. Mechanistic studies by control experiments, electrochemical measurements and in‐situ NMR spectra proposed a N–O bond interruption/C–C bond fragmentation/oxidation sequence to provide the key cation intermediate for the next electrophilic S N process. The features of mild condition, short reaction time and broad substrate scope made this new strategy much promising in the transformation of benzyl compounds, which might be valuable in last‐stage functionalizations.

  • [期刊] Enantiocomplementary C-H Bond Hydroxylation Combining Photo-Catalysis and Whole-Cell Biocatalysis in a One-Pot Cascade Process
    Enantiocomplementary hydroxylation of alkyl aromatics through a one-pot photo-biocatalytic cascade reaction is described. The photoredox process is implemented in aqueous phase with O-2 as oxidant and the subsequent (R)- or (S)-selective bioreduction is performed by whole cell system without the addition of the expensive cofactor (NADPH). This mild, operationally simple protocol transforms a wide variety of readily available aromatic compounds into valuable chiral alcohols with high yield (up to 90 %) and stereoselectivity (up to 99 %), thereby displaying important potentials in organic synthesis.
  • [期刊] Cover Feature: Visible‐Light‐Induced Dearomatizations (Eur. J. Org. Chem. 10/2020)
  • [期刊] Quantitative Mono-Formation and Crystallographic Characterization of Pyrazole- and Pyrrole-Ring Fused Derivatives of C-60
    Nitrogen-heterocyclic fullerene derivatives have received great interest in the past years due to their potential biological activities and optical properties. Herein, we report a quantitative mono-formation of the pyrazole- and pyrrole-ring fused derivatives of fullerene C-60, i.e., C-60 (C13N2H10) (3) and C-60 (C9NH11) (4), from the respective reactions between C-60 and diphenylnitrilimine (1) and N-benzylazomethine ylide (2). Single-crystal X-ray diffraction (XRD) crystallographic results unambiguously confirm the formation of [6,6]-closed derivatives (3 and 4). Interestingly, the intermolecular pi-pi interactions between the phenyl groups and C-60 spheres are observed in the crystal of 3, but they are absent from 4, indicating that the number of the external phenyl groups has an important influence on the stacking pattern of derivatives during crystallization. Electrochemical results show that the reduction potentials of 3 are positively shifted compared with the corresponding values of pristine C-60, while the reduction potentials of 4 are all cathodically shifted, revealing the redox processes of C-60 can be selectively modulated by changing the structures of the addends. Notably, our theoretical results demonstrate that the quantitative formation of merely one mono-adduct without any bis- or multi-adducts detected in both reactions is a direct result from the steric hindrance of the existing bulky pyrazole- or pyrrole-ring moiety on the C-60 cage. This work thus presents a quantitative way for the mono-formation of the pyrrole- and pyrazole-ring fused derivatives of C-60, which are potentially useful as organic photovoltaic devices and biological reagents.
  • [期刊] Amphiphilic Pd-II-NHC Complexes on 1,3-Alternate p-tert-Butylthiacalix[4]arene Platform: Synthesis and Catalytic Activities in Coupling and Hydrogenation Reactions
    Herein we report the first example of amphiphilic Pd-II-NHC complexes on the thiacalix[4]arene backbone in 1,3-alternate configuration. Relative catalytic activity of synthesized Pd-II-NHC complexes in Suzuki-Miyaura coupling of haloarenes with phenylboronic acid was studied. A combination of micellar and metallocomplex catalysis was observed in Suzuki-Miyaura coupling upon going from pure DMF to water/DMF 3:1: the 2-fold increase of conversion of 4-bromoanisole unlike pure DMF was found. Interesting feature was found using chloroarene in DMF/water: the reaction selectivity changed from heterocoupling to homo coupling of phenylboronic acid. Pd-II-NHC complexes demonstrated a high activity in model hydrogenation reaction of p-nitrophenol using sodium borohydride. The most lipophilic Pd-II-NHC complex was found to be most active, which can be attributed with additional p-nitrophenol preconcentration in the aggregates due to larger hydrophobic capacity of macrocycle.
  • [期刊] Synthesis and Characterization of Naphtho[2,1-b:7,8-b ']bis[1]benzothiophene
    We describe a simple three-step synthesis of naphtho[2,1-b:7,8-b ']bis[1]benzothiophene, which is scalable to multi-hundred-gram. We report the subsequent functionalization of this compound into iodine, boronic ester and silane derivatives, which are useful intermediates for various applications. The core structure was analyzed by NMR and single-crystal X-ray diffraction, and the physical properties were investigated by cyclic voltammetry, UV/Vis- and fluorescence spectroscopy.
  • [期刊] Glycosylation on Unprotected or Partially Protected Acceptors
    Over the last 30 years, there have been several methods developed for the synthesis of oligosaccharides, such as combinatorial synthesis, programmable one-pot glycosylations, pre-activation-based chemo-selective glycosylation strategy, random glycosylation, chemo-enzymatic processes, and automated platforms. Distinguishing hydroxyl groups in carbohydrate monomers form the crux of oligosaccharides synthesis. The protection of hydroxyl groups stops glycosylation at undesired positions on carbohydrates, but additional steps are required to install and remove the protecting groups. The targeted functionalization of carbohydrates relies mostly on the protection of hydroxyl groups that are not supposed to undergo glycosylation and to leave the hydroxyl group unprotected where the glycosylation should occur. Numerous procedures to avoid or decrease protecting group manipulations have been developed for the synthesis of a single or an oligosaccharide library, such as glycosylation on unprotected or partially protected acceptors, and random glycosylation on unprotected acceptors. In this review, overall approaches for glycosylation on unprotected or partially protected acceptors in the synthesis of oligosaccharides and oligosaccharide libraries are summarized, the glycosylation on unprotected or partially protected carbohydrate acceptors with or without tin or boron mediation, and random glycosylation on unprotected or partially protected acceptors in solution phase or on solid phase are discussed.
  • [期刊] Nitrene Transfer Reactions for Asymmetric C-H Amination: Recent Development
    C-H bonds are ubiquitous and abundant in organic molecules. If C-H bonds could be directly converted to desired functional groups in a chemo-, site-, and stereoselective manner, C-H functionalization would be a strong and useful tool for organic synthesis. Recent developments in catalytic and enzymatic chemistry have achieved highly sustainable and selective nitrene C-H insertion. Initially, C-H amination was inspired by model studies on enzymatic oxidation and used iminoiodinanes, nitrogen analogs of iodosobenzene, as nitrene precursors. Transition-metal/iminoiodinane systems are well studied and established. These systems can directly introduce sulfonamide groups with excellent stereoselectivity, albeit with co-production of iodobenzene as waste material. Fortunately, the atom economics of this methodology were improved by introducing highly sustainable nitrene sources such as azide compounds and 1,2,4-dioxazol-5-one derivatives. In this review, we present the details of these developments with respect to their catalysts and nitrene sources.
  • [期刊] Macrolide Core Synthesis of Calysolin IX Using an Intramolecular Glycosylation Approach
    The utility of intramolecular glycosylation for the synthesis of the 27-membered macrocyclic ring is highlighted in this first total synthesis of the most complex resin glycoside isolated to date - Calysolin IX. Oligosaccharide-containing macrolides core was effectively constructed by TfOH/NIS-promoted intramolecular glycosylation of thioglycosyl donor. As the glycosidic bond must be created en route to target structure, we show that this unusual yet efficient approach can effectively reduce the number of steps in the total synthesis of complex natural macrolides. This attempt is documented as an efficient tool in the synthesis of gigantic macrolide rings thus proving their practical utility in the total synthesis of sugar-containing targets.