Ruthenium- and Copper-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohol Derivatives with Hydrazones

Ruthenium- and copper-catalyzed propargylic substitution reactions of propargylic alcohol derivatives with N-monosubstituted hydrazones as ambident nucleophiles are achieved in which N-monosubstituted hydrazones exhibit impressive different reactivities depending on different catalytic systems, behaving as carbon-centered nucleophiles to give the corresponding propargylic alkylated products in ruthenium catalysis, or as nitrogen-centered nucleophiles to afford the corresponding propargylic aminated products in copper catalysis. DFT calculations were carried out to investigate the detailed reaction pathways of these two systems. Further transformation of propargylic substituted products affords the corresponding multisubstituted pyrazoles as cyclization products in good to high yields.

Ruthenium-Catalyzed Enantioselective Propargylic Phosphinylation of Propargylic Alcohols with Phosphine Oxides

The development of transition metal-catalyzed enantioselective propargylic substitution reactions has gained much progress in recent years, however, no successful example with phosphorus-centered nucleophiles has yet been reported until now. Herein, we report the first successful example of ruthenium-catalyzed enantioselective propargylic substitution reactions of propargylic alcohols with diarylphosphine oxides as phosphorus-centered nucleophiles. This synthetic approach provides a new method to prepare chiral phosphorus-containing organic compounds.

K2CO3 Promoted Cascade Reaction for the Preparation of 1H-Imidazol-4- yl-1-amine Derivatives

:

A K2CO3 promoted efficient one pot two-step method for the preparation of 1H-imidazol-4- yl-1-amine derivatives has been developed. A series of second amines with an imidazole group were obtained with 56%-91% yields by the K2CO3 promoted amination of acetates and nitrogen deprotection of the imidazole process.

Enhancing Potency and Selectivity of a DC-SIGN Glycomimetic Ligand by Fragment-Based Design: Structural Basis

Chemical modification of pseudo-dimannoside ligands guided by fragment-based design allowed for the exploitation of an ammonium-binding region in the vicinity of the mannose-binding site of DC-SIGN, leading to the synthesis of a glycomimetic antagonist (compound 16) of unprecedented affinity and selectivity against the related lectin langerin. Here, the computational design of pseudo-dimannoside derivatives as DC-SIGN ligands, their synthesis, their evaluation as DC-SIGN selective antagonists, the biophysical characterization of the DC-SIGN/16 complex, and the structural basis for the ligand activity are presented. On the way to the characterization of this ligand, an unusual bridging interaction within the crystals shed light on the plasticity and potential secondary binding sites within the DC-SIGN carbohydrate recognition domain.

Efficient Synthesis of N-Alkylated 4-Pyridones by Copper-Catalyzed Intermolecular Asymmetric Propargylic Amination

Copper-catalyzed intermolecular asymmetric propargylic amination with 4-hydroxypyridines has been realized for the first time. In the presence of Cu complex derived from Pybox ligand, the N-propargylated 4-pyridones were obtained under mild reaction conditions with up to 99 % yield and 95 % ee. The Pybox ligand bearing a 4-F-phenyl substituent plays a key role for the high enantioselectivity. The products can be easily transformed to the core structure of quinolizidine alkaloids.

Catalytic Nucleophilic Fluorination of Secondary and Tertiary Propargylic Electrophiles with a Copper-N-Heterocyclic Carbene Complex

A catalytic method for the nucleophilic fluorination of propargylic electrophiles is described. Our protocol involves the use of a Cu(NHC) complex as the catalyst and is suitable for the preparation of secondary and tertiary propargylic fluorides without the formation of isomeric fluoroallenes. Preliminary mechanistic investigations suggest that fluorination proceeds via copper acetylides and that cationic species are involved.