Regioselective reduction of keto groups in Michael adducts of levoglucosenone and cyclohexanone

Conditions for the highly regioselective reduction of the specified keto groups in the Michael adduct of levoglucosenone and cyclohexanone have been developed. Selective reduction of the keto group in the cyclohexanone moiety was performed under the action of lithium metal in NH₃/THF system. Reduction of the keto group in the carbohydrate residue was accomplished microbiologically or by refluxing with NaBH(OAc)₃ in benzene.     

NHC-assisted Ni(II)-catalyzed acceptorless dehydrogenation of amines and secondary alcohols

A novel catalytic system including NiCl₂-NHC ligand precursor has been developed for the preparation of imines from amines and ketones from alcohols. Owing to the acceptorless dehydrogenation pathway for this reaction, the hydrogen gas is liberated as a by-product. The active catalyst is generated in situ by the reaction of nickel (II) chloride, bis (imidazolium) chlorides and potassium tert-butoxide. The products were obtained in good to excellent yields and a wide variety of amines and ketones were applied successfully in this protocol.     

X-ray structure and conformation of some enol acetates derived from simple ketones

The conformational arrangements of a series of enol acetates derived from simple ketones have been examined by X-ray crystallography. For this series, the carbonyl enol motif was found to adopt a similar conformation.     

Hexafluoroacetone as a protecting and activating reagent: 5,5-difluoro- and trans-5-fluoropipecolic acids from glutamic acid

Starting from hexafluoroacetone-protected (S)-glutamic acid, trans-5-fluoropipecolic and 5,5-difluoropipecolic acid have been synthesized. The piperidine ring was constructed by an intramolecular metal carbenoid NH insertion.     

InCl3/SiO2-catalyzed α-amination of 1,3-dicarbonyl compounds under microwave irradiation

A variety of 1,3-dicarbonyl compounds undergo smooth α-amination with diethyl azodicarboxylate (DEAD) on the surface of silica gel impregnated with indium trichloride under microwave irradiation and solvent-free conditions. Improved yields and enhanced reaction rates were observed.     

4H-3,1-benzoxazines from <Emphasis Type="Italic">o</Emphasis>-aminoacylbenzenes

A new efficient method has been proposed for the synthesis of 4H-3,1-benzoxazines from 2-aminoacylbenzenes. This reaction sequence may be used either for 2-aminoaryl alkyl ketones or 2-aminobenzophenones. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 941–954, June, 2007.     

Heterogeneously catalyzed efficient hydration of alkynes to ketones by tin-tungsten mixed oxides

The Sn–W mixed oxide prepared by calcination of the Sn–W mixed hydroxide precursor with a Sn/W molar ratio of 2:1 at 800 °C (SnW2‐800) acts as an efficient heterogeneous catalyst for the hydration of alkynes. Structurally diverse terminal and internal alkynes, including aromatic, aliphatic, and double‐bond‐containing ones, can be converted into the corresponding ketones in moderate to high yields. The catalytic activity of SnW2‐800 is much higher than those of previously reported heterogeneous catalysts and commonly utilized acid catalysts. The observed catalysis was truly heterogeneous, and the retrieved catalyst can be reused at least three times with retention of its high catalytic performance. The reaction rate for the SnW2‐800‐catalyzed hydration was decreased by addition of 2,6‐lutidine and the hydration hardly proceeded in the presence of an equimolar amount of this compound with respect to that of the Brønsted acid sites in SnW2‐800. Therefore, the present hydration is mainly promoted by the Brønsted acid sites in SnW2‐800.     

One‐Pot Synthesis of 1,4‐Dihydro‐2‐thioxo‐2H‐3,1‐benzoxazine‐4‐acetic Acid Derivatives by the Reaction of 2‐Isothiocyanatophenyl Ketones with Lithium Enolates of Acetates and Tertiary Acetamides

The one‐pot synthesis of 4‐aryl‐1,4‐dihydro‐2‐thioxo‐2H‐3,1‐benzoxazine‐4‐acetic acid derivatives 2 was achieved in good yields by the reaction of aryl(2‐isothiocyanatophenyl)methanones 1 with lithium enolates of acetates and tertiary acetamides. (2E)‐1‐(2‐Isothiocyanatophenyl)‐3‐phenylprop‐2‐en‐1‐one ( 3 ) gave 1,4‐dihydro‐4‐[(1E)‐2‐phenylethenyl]‐2‐thioxo‐2H‐3,1‐benzoxazine‐4‐acetic acid derivatives 4 in good yields as well.     

Application of Ni(II) complexes of air stable Schiff base functionalized N-heterocyclic carbene ligands as catalysts for the transfer hydrogenation of aliphatic ketones

Abstract

New air stable N-heterocyclic carbene functionalized Schiff base ligands (L) of the type 2-[-2-[3-(R)imidazol-1-yl]ethyliminomethyl]phenol [R?=?methyl (2), 2-pyridylmethyl (3)] were synthesized and characterized by NMR, IR, MS, and CHN analysis. Single crystal X-ray structural analysis of their Ni(II) complexes revealed square planar arrangement of the chelating ligands coordinated in tridentate (2, C^N^O) and tetradentate (3, N^C^N^O) modes around the metal. The three new isolated and fully characterized complexes were utilized as catalysts for the catalytic transfer hydrogenation of aliphatic ketones in 2-propanol as solvent and source of hydrogen. Based on 0.2?mol% catalyst concentration, the complexes showed activity for aliphatic ketones and 100% conversion (turnover number of 500) for cyclohexanone and all the aromatic ketones tested.     

Asymmetric Inverse-Electron-Demand Hetero-Diels–Alder Reaction for the Construction of Bicyclic Skeletons with Multiple Stereocenters by Using a Bifunctional Organocatalytic Strategy: An Efficient Approach to Chiral Macrolides

We have performed the first bifunctional organocatalytic highly enantioselective inverse-electron-demand hetero-Diels–Alder reaction of cyclic ketones with enones to afford densely functionalized bicyclic skeletons that contain three stereocenters (up 82 % yield, 10:1 d.r., and 97 % ee). Unlike the previous IEDDAR catalytic strategy, this method features a double HOMO_dienophile/ LUMO_diene-activated pathway. Moreover, this process provides a promising method for the construction of enantioenriched macrolides.