Selective Manganese‐Catalyzed Oxidation of Hydrosilanes to Silanols under Neutral Reaction Conditions

The first manganese‐catalyzed oxidation of organosilanes to silanols with H₂O₂ under neutral reaction conditions has been accomplished. A variety of organosilanes with alkyl, aryl, alknyl, and heterocyclic substituents were tolerated, as well as sterically hindered organosilanes. The oxidation appears to proceed by a concerted process involving a manganese hydroperoxide species. Featuring mild reaction conditions, fast oxidation, and no waste byproducts, the protocol allows a low‐cost, eco‐benign synthesis of both silanols and silanediols.     

Synthesis of Highly Substituted Pyridines through Copper‐Catalyzed Condensation of Oximes and α,β‐Unsaturated Imines

A copper‐catalyzed condensation reaction of oxime acetates and α,β‐unsaturated ketimines to give pyridine derivatives is reported. The reaction features mild conditions, high functional‐group compatibility, and high regioselectivity with respect to unsymmetrical oxime acetates, thus allowing the preparation of a wide range of polysubstituted pyridines, many of which are not readily accessible by conventional condensation methods.     

Copper‐Complex‐Catalyzed Asymmetric Aerobic Oxidative Cross‐Coupling of 2‐Naphthols: Enantioselective Synthesis of 3,3′‐Substituted C1‐Symmetric BINOLs

A novel chiral 1,5‐N,N‐bidentate ligand based on a spirocyclic pyrrolidine oxazoline backbone was designed and prepared, and it coordinates CuBr in situ to form an unprecedented catalyst that enables efficient oxidative cross‐coupling of 2‐naphthols. Air serves as an external oxidant and generates a series of C₁‐symmetric chiral BINOL derivatives with high enantioselectivity (up to 99 % ee) and good yield (up to 87 %). This approach is tolerant of a broader substrates scope, particularly substrates bearing various 3‐ and 3′‐substituents. A preliminary investigation using one of the obtained C₁‐symmetric BINOL products was used as an organocatalyst, exhibiting better enantioselectivity than the previously reported organocatalyst, for the asymmetric α‐alkylation of amino esters.     

Diastereodivergent Asymmetric 1,3‐Dipolar Cycloaddition of Azomethine Ylides and β‐Fluoroalkyl Vinylsulfones: Low Copper(II) Catalyst Loading and Theoretical Studies

A Cu^II‐catalyzed asymmetric 1,3‐dipolar cycloaddition using β‐fluoroalkyl alkenyl arylsulfones as dipolarophiles and glycine/alanine iminoesters as azomethine ylide precursors has been developed. Remarkably, a catalyst loading as low as 0.5 mol % is highly efficient. Accordingly, a wide range of enantioenriched 3‐fluoroalkyl pyrrolidines, as well as Δ²‐pyrroline and pyrrole derivatives, are generated in good to excellent yields with high asymmetric induction. This synthetic approach is diastereodivergent in that exo‐adducts could be converted into the corresponding exo′‐adducts by 1,8‐diazabicyclo[5.4.0]undec‐7‐ene mediated epimerization at C2 of the pyrrolidine core. The free‐energy profiles from DFT calculations suggest the Michael addition of the 1,3‐dipole to be the rate‐ and enantiodetermining step, and the origin of stereoselectivity is studied by means of the noncovalent interaction (NCI) analysis.     

Interrupted Pummerer Reaction in Latent‐Active Glycosylation: Glycosyl Donors with a Recyclable and Regenerative Leaving Group

Latent O‐glycosides, 2‐(2‐propylthiol)benzyl (PTB) glycosides, were converted into the corresponding active glycosyl donors, 2‐(2‐propylsulfinyl)benzyl (PSB) glycosides, by a simple and efficient oxidation. Treatment of the PSB donor and various acceptors with triflic anhydride provided the desired glycosides in good to excellent yields. The leaving group, which was activated by an interrupted Pummerer reaction, can be recycled (PSB‐OH) and regenerated as the precursor (PTB‐OH). A natural hepatoprotective glycoside, leonoside F, was efficiently synthesized in a convergent [3+1] manner with this newly developed method. The present total synthesis also led to a structural revision of this phenylethanoid glycoside.     

Quinine‐Catalyzed Asymmetric Synthesis of 2,2′‐Binaphthol‐Type Biaryls under Mild Reaction Conditions

Simple quinine as an organocatalyst mediates the addition of various naphthols to halogenated quinones to afford non‐C₂‐symmetrical, axially chiral biaryl products, which are promising compounds as chiral ligands and organocatalysts. The rotational barrier required to have two distinct atropisomers has been evaluated in the products generated from the addition of naphthols to various quinones by means of DFT calculations and HPLC. The use of halogenated quinones as reagents was necessary to have configurationally stable enantiomeric products which can be obtained in good yield and stereoselectivity. These compounds have also been prepared in gram quantities and recrystallized to near enantiopurity.