Hydrogen Acceptor‐ and Base‐Free N‐Formylation of Nitriles and Amines using Methanol as C1 Source

An N‐formylation method using methanol as the C₁ source without a stoichiometric amount of activating reagent is described. Nitriles as well as amines can be directly used as substrates. The reaction is catalyzed by an N‐heterocyclic carbene coordinated ruthenium(II) dihydride complex, which mediates methanol dehydrogenation, nitrile reduction, and C N bond formation without any external base, hydrogen acceptor, or oxidant.

     

N‐Heterocyclic Carbene‐Catalyzed Umpolung Formal [3+3] Cycloaddition of Enals with Isatogens: Access to Fused Indolin‐3‐ones with a Tetrasubstituted Carbon Stereocenter

A novel synthetic method to access fused indolin‐3‐ones with a tetrasubstituted carbon stereocenter has been developed via NHC‐catalyzed umpolung formal [3+3] cycloaddtion of enals with isatogens. This methodology could be also applied for the quick construction of the 6‐5‐5 tricyclic pyrrolo[1,2‐a]indole skeleton which is frequently found as a core structure of many indole alkaloids.

     

When NHC Ligands Make a Difference in Gold Catalysis

Thanks to their unique electronic and steric properties, carbene ligands offer highly valuable features for catalysis, including homogenous gold catalysis. The use of carbene-gold complexes has improved existing reactions, either by modifying reactivity modes or by leading to highly asymmetric processes. These topics will be discussed on the basis of selected examples.     

第二代Grubbs催化剂配体的合成及优化

Grubbs催化剂是一种用于烯烃复分解反应的配位化合物,其中的配体对于催化剂的催化性能、稳定性有很大的影响。目前,N-杂环卡宾(N-heterocyclic carbenes,NHC)是第二代Grubbs催化剂中的一个关键配体。本文以乙二醛为原料,通过取代、还原、环化等反应,合成了一种氮杂环卡宾的前驱体1,3-二取代-2-羧基咪唑啉。在此基础上,对部分关键合成环节进行了优化。研究结果表明,在乙二醛-双-(2,4,6三甲基苯基)亚胺的合成过程中,随着反应温度的升高,产率逐渐升高,后有所降低。在3-(2,4,6三甲基苯基)-2-羧基咪唑啉的合成过程中,反应时间对收率影响最大。     

The Reactivity of Difluorocarbene with Hydroxylamines: Synthesis of Carbamoyl Fluorides

Carbamoyl fluorides are formed in reactions of hydroxylamines with difluorocarbene generated from sodium bromodifluoroacetate as readily available and non‐toxic carbene precursor. The process shows a high functional group tolerance, and the reaction path has been rationalized by computational calculations.

     

Simple N‐Heterocyclic Carbenes as Ligands in Ullmann‐Type Ether and Thioether Formations

A simple N‐heterocyclic carbene (NHC) derived from 1‐methyl‐3‐ethylimidazolium tetrafluoroborate was found to be an efficient ligand for a range of copper‐catalyzed cross‐coupling reactions, leading to the formation of aromatic ethers and thioethers.

     

Gold(I)‐Catalysed Cyclisation of Alkynoic Acids: Towards an Efficient and Eco‐Friendly Synthesis of γ‐, δ‐ and ϵ‐Lactones

The improved synthesis of γ‐, δ‐ and ϵ‐lactones using a dinuclear N‐heterocyclic carbene (NHC)‐gold(I) catalyst is reported. This solvent‐free process provides access to γ‐ and δ‐lactones in high regio‐ and stereoselectivity. Reactions were performed at low catalyst loadings and without the need for any additives. The use of a digold pre‐catalyst provides a new synthetic route to functionalised ϵ‐lactones, poorly accessible using previous methodologies.

     

Synthesis of Amido‐N‐imidazolium Salts and their Applications as Ligands in Suzuki–Miyaura Reactions: Coupling of Hetero‐ aromatic Halides and the Synthesis of Milrinone and Irbesartan

A new catalytic system based on palladium‐amido‐N‐heterocyclic carbenes for Suzuki–Miyaura coupling reactions of heteroaryl bromides is described. A variety of sterically bulky, amido‐N‐imidazolium salts were synthesized in high yields from the corresponding anilines. This catalytic system effectively promoted Suzuki–Miyaura couplings of heteroaryl bromides and chlorides with a range of boronic acids to give the corresponding aryl compounds in high yield. The yield was increased with increasing steric bulkiness of the substituted group. Especially, 1‐(2,6‐diisopropylphenyl)‐3‐N‐(2,4,6‐tri‐tert‐butylphenylacetamido)imidazolium bromide ( 4bc ) exhibited 850,000 TON in the coupling reaction of 2‐bromopyridine and phenylboronic acid. In addition, pharmaceutical compounds such as milrinone and irbesartan were synthesized via Suzuki–Miyaura coupling using sterically bulky, amido‐N‐imidazolium salt ( 4bc ) as a ligand.