NAD(P)H辅酶模型在Mg2+离子催化条件下还原N-芳基芴亚胺反应的研究

对Hantzsch酯在Mg²⁺存在和不存在的情况下还原N-芳基芴亚胺的反应进行了研究, 并与BNAH的类似还原做了系统的比较.研究结果表明:Mg²⁺在该还原反应中起亲电催化剂的作用;还原能力较BNAH弱的Hantzsch酯在反应中所呈现的强的反应性是由于其3, 5-位两个极性谈基氧通过静电作用降低过渡态的能量的缘故;本文反应届H-一步转移机理.     

Complementary routes to both enantiomers of pipecolic acid and 4,5-dihydroxypipecolic acid derivatives

Complementary new routes to both enantiomers of N-protected pipecolic acid and the corresponding 4,5-dihydroxylated derivatives are developed, which involve stereo-divergent allylation of a chiral N-allylimine and ring-closing metathesis as key steps.     

Allylic amination of unfunctionalyzed olefins by nitroarenes and CO, catalyzed by Ru3(CO)12/Ph-BIAN (Ph-BIAN=bis(phenylimino)acenaphthenequinone): extension to the synthesis of allylic amines with strongly electron-withdrawing or electron-donating groups on the aryl ring

The allylic amination of unfunctionalyzed olefins by nitroarenes under CO pressure, catalyzed by Ru₃(CO)₁₂/Ph-BIAN (Ph-BIAN=bis(phenylimino)acenaphthenequinone) has been extended to some substrates with strongly electron-withdrawing groups on the nitroarene. Reaction of 1,4-dinitrobenzene selectively affords functionalization of only one nitro group, the other remaining unreacted. However, the second nitro group can be reduced in one pot by CO/H₂O in the presence of the same catalytic system employed in the amination reaction, to afford the corresponding 4-amino derivative. Some attempts to render the reaction enantioselective by employing chiral bis-oxazolines as ligands in place of Ph-BIAN are described. Bis-oxazolines are suitable ligands for the reaction, although not as efficient as Ph-BIAN, but the allylic amine obtained was found to be racemic.     

Synthesis and l-fucosidase inhibitory activity of a new series of cyclic sugar imines—in situ formation and assay of their saturated counterparts

The synthesis of a series of aryl-substituted cyclic sugar imines was performed via a tandem nucleophilic addition/substitution reaction. The so-obtained ketimines displayed fucosidase inhibitory activities (IC₅₀ = 46-556 μM). Their reduced counterparts were prepared and assayed after addition of sodium borohydride to the enzymatic assay stock solution. The pyrrolidines strongly inhibit fucosidase (IC₅₀ = 0.65-150 μM).     

Trimethylsilyl cyanide addition to aldimines and its application in the synthesis of (S)-phenylglycine methyl ester

The addition of TMSCN to a variety of arylaldimines (Strecker reaction) in the presence of LiClO₄ or BF₃·Et₂O in acetonitrile has been studied. The reaction provided the addition products in very high yields. The method has been successfully utilized for the synthesis of (S)-phenylglycine methyl ester.     

Convenient synthesis of mono- and di-β-hydroxy-β-bis(trifluoromethyl)-(di)imines from β-hydroxy-β-bis(trifluoromethyl)-ketones and (di)amines

A series of novel β-hydroxy-β-bis(trifluoromethyl)-imines (2a-j) and di(β-hydroxy-β-bis(trifluoromethyl))-diimines (3a-f) were prepared in moderate to good yields via a simple two-step approach: first, β-hydroxy-β-bis(trifluoromethyl)-ketones (1a-c) were obtained by a catalyst-free aldol reaction between liquid hexafluoroacetone sesquihydrate and ketones (acetone, acetophenone, and pinacolone, respectively); then, condensation of the latter fluorinated β-ketols 1a-c with primary amines or diamines was achieved in the presence of Lewis (montmorillonite, InBr₃, La(OTf)₃) or Brönsted (PTSA) acid catalysts. The molecular structures of mono- and di-β-hydroxy-β-bis(trifluoromethyl)-(di)imines 2e,h and 3a,f were determined and found to exhibit strong intramolecular (R)N?H-O hydrogen bonding.     

Alkyl Formates as Transfer Hydroalkylation Reagents and Their Use in the Catalytic Conversion of Imines to Alkylamines**

Easily accessible via a simple esterification of alcohols with formic acid, alkyl formates are used as a novel class of transfer hydroalkylation reagents, CO₂ acting as a traceless linker. As a proof-of-concept, their reactivity in the transfer hydroalkylation of imines is investigated, using a ruthenium-based catalyst and LiI as promoter to cleave the C−O σ-bond of the formate scaffold. Providing tertiary amines, the reaction displays a divergent regioselectivity compared to previously reported transfer hydroalkylation strategies.     

Front Cover: Dynamic Covalent Chemistry for Synthesis and Co-conformational Control of Mechanically Interlocked Molecules (Eur. J. Org. Chem. 8/2023)

Mechanically interlocked molecules have found extensive applications in areas all across the physical sciences, from materials to catalysis and sensing. However, introducing mechanical bonds and entanglements at the molecular level is still a significant challenge due to the inherent restriction in entropy needed to preorganize strands before interlocking. Over the last decade, dynamic covalent chemistry has emerged as one of the most efficient methods of forming rotaxanes, catenanes and molecular knots. By using reversible bonds such as imines, disulfides and boronate esters, one can use the inherent error-correction in these linkages to form interlocked architectures with high fidelity and often in excellent yields. This review reports on recent advances in the use of dynamic covalent chemistry to make mechanically interlocked molecules, systematically surveying clipping, capping and templating approaches with dynamic bonds. Furthermore, it is also discussed how dynamic bonds can be used to control motion, co-conformational expression and catalytic activity in mechanically interlocked molecular machinery.     

Fluoro aromatic imine nickel(0) complexes: Synthesis and structural studies

The reaction of [Ni(dippe)]₂(μ-H)₂ with a series of fluoroaromatic imines affords nickel(0) complexes of the type [(dippe)Ni(η²-C,N)-PhHCNR′Ph], dippe = 1,2-bis(diisopropylphosphine)ethane. Solution NMR experiments as well as X-ray diffraction studies confirmed the π-coordination of the ligand through the CN moiety; the resulting complex found to adopt a distorted tetrahedral geometry around the nickel center. The compounds are thermally stable and decomposition is only observed after long periods of heating above 150 °C.     

Gas-phase reactions of the bis(η-cyclopentadienyl)methylzirconium cation with imines

The reactions of the bis(η⁵-cyclopentadienyl)methylzirconium cation (1) with four imines have been studied in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry. Reactivity of the bis(η⁵-cyclopentadienyl)methylzirconium cation is governed by the availability of a labile hydrogen in the corresponding imine. The products observed differ from those that might be expected in analogy with earlier work on ketones, aldehydes and alkenes (e.g., zirconocene η³-enolate and η³-allyl complexes): azomethyne/benzylidene species are found instead of enamines; however, the general reaction mechanism resembles that proposed for ketones and alkenes. An elimination reaction leading to final products was shown to be preceded by a fast migratory insertion/deinsertion equilibrium for alkyl-substituted imines. Such an equilibrium is not possible for aryl-substituted imines due to lack of lability of the aryl groups and thus only methane elimination was observed for these imines.