Interaction of Methyl N-(3-oxoalkyl)carbamates, S-methyl -Carbamates, and -Dithiocarbamates with Sodium Borohydride. Synthesis of Tetrahydro-1,3-oxazin-2-ones and -thiones

The interaction of N-(3-oxoalkyl)carbamates, -thiocarbamates, and -dithiocarbamates with sodium borohydride has been studied. It was shown that reaction proceeds diastereoselectively, and reductive cyclization with the formation of tetrahydro-1,3-oxazin-2-ones and -thiones may occur. The tend to cyclization of the N-(3-hydroxyalkyl)carbamates, -thiocarbamates, and -dithiocarbamates formed as intermediates depends on the number of substituents in the alkyl chain.     

How the [NiFe4S4] Cluster of CO Dehydrogenase Activates CO2 and NCO−

Ni,Fe‐containing CO dehydrogenases (CODHs) use a [NiFe₄S₄] cluster, termed cluster C, to reversibly reduce CO₂ to CO with high turnover number. Binding to Ni and Fe activates CO₂, but current crystal structures have insufficient resolution to analyze the geometry of bound CO₂ and reveal the extent and nature of its activation. The crystal structures of CODH in complex with CO₂ and the isoelectronic inhibitor NCO^? are reported at true atomic resolution (d_min≤1.1 Å). Like CO₂, NCO^? is a μ₂,η² ligand of the cluster and acts as a mechanism‐based inhibitor. While bound CO₂ has the geometry of a carboxylate group, NCO^? is transformed into a carbamoyl group, thus indicating that both molecules undergo a formal two‐electron reduction after binding and are stabilized by substantial π backbonding. The structures reveal the combination of stable μ₂,η² coordination by Ni and Fe2 with reductive activation as the basis for both the turnover of CO₂ and inhibition by NCO^?.     

A synthesis of camptothecin

A total synthesis of camptothecin has been carried out. Central to our synthesis is the intramolecular condensation of a suitably designed ketol, which in turn was obtained from a tricyclic ABC ring synthon. A tandem reductive amination and Michael addition sequence on an unsaturated quinoline ester was employed for the assembly of the ABC skeleton.     

Direct reductive amination using triethylsilane and catalytic bismuth(III) chloride

Direct reductive amination (DRA) using triethylsilane (TESH) and catalytic bismuth(III) chloride (BiCl₃) is described for the first time. The use of TESH and BiCl₃ provides easy handling, low cost, non-toxicity, and a mild Lewis acid activity, thereby meeting the demand for green and sustainable chemistry. The developed DRA is highly chemoselective and applicable to less-basic amines. The experimental results of this study revealed that the developed DRA could be catalyzed by BiCl₃, which was gradually reduced to Bi(0) or bismuth with a low valency by TESH, but TESCl, Bi(0), and Bi(0) with TESCl catalyzed the DRA to some extent.     

Operationally convenient asymmetric synthesis of (S)- and (R)-3-amino-4,4,4-trifluorobutanoic acid: Part I: Enantioselective biomimetic transamination of isopropyl 4,4,4-trifluoro-3-oxo-butanoate

DBU-catalyzed asymmetric synthesis of (S)- and (R)-3-amino-4,4,4-trifluorobutanoic acid via enantioselective biomimetic transamination of isopropyl 4,4,4-trifluoro-3-oxobutanoate with (R)- and (S)-phenylethylamine has been developed. The effect of the base concentration of the reaction rate and stereochemical outcome has been systematically studied. The key reaction step, DBU-catalyzed 1,3-proton shift transfer was found to be highly enantioselective (>95% ee). However, due to some racemization of the intermediate Schiff base under the highly basic reaction conditions leads to the final product of lower enantiomeric purity.     

Study of metal-supported carbon matrix as a high-capacity anode for Li-ion battery

Tin–graphite composite with 20 wt. % metal content as well as its structural and electrochemical characteristics are presented. Synthetic graphite—super flake type—was used as object for the modification experiment. Chemical reduction was applied for the loading process, which was carried out under inert argon atmosphere. Composite with specific morphology and improved electrochemical behavior was prepared. The obtained material shows higher discharge capacity as well as increased initial charge–discharge coulomb efficiency, compared with the unmodified one. The supporting metal morphology, the type of graphite, and the preparation process taken together generally affect the improvement of the electrochemical performance. This work was presented at the 11th Euro Conference on Science and Technology of Ionics, Batz-sur-Mer, France, Sept. 9–15, 2007.     

Theoretical studies on the reductive elimination reaction mechanism from neutral palladium(IV) sulfinate complexes

Detailed reaction mechanisms of reductive elimination from neutral palladium(IV) sulfinate complex have been investigated with the aid of density functional theory calculations. The calculation results reveal that the neutral palladium(IV) sulfinate complexes have four possible reductive elimination pathways via the C–S, C–C, C–Cl, and desulfitative C–C bond formation to give different products, and the formation of the C–S bond‐containing product is kinetically more favorable over the formation of other products. Present calculations provide new insights into the organopalladium(IV) chemistry and C–S bond activation. Copyright © 2013 John Wiley & Sons, Ltd.     

Photoinduced Nickel-Catalyzed Carbon–Heteroatom Coupling**

Herein, we report visible light-promoted single nickel catalysis for diverse carbon–heteroatom couplings under mild conditions. This mild, general, and robust method to couple diverse nitrogen, oxygen, and sulfur nucleophiles with aryl(heteroaryl)/alkenyl iodides/bromides exhibits a wide functional group tolerance and is applicable to late-stage modification of pharmaceuticals and natural products. On the base of preliminary mechanistic studies, a Ni^I/Ni^III cycle via the generation of active Ni^I complexes that appear from homolysis of Ni^II−I rather than Ni^II−aryl bond was tentatively proposed.     

Reductive α-alkylation of ketones with aldehydes at atmospheric pressure of carbon monoxide: the effect of fluoride activation in ruthenium catalysis

Fluoride additive to [(p-cymene)RuCl₂]₂, a readily available ruthenium catalyst, allows one to achieve milder conditions for the reductive alkylation of aldehydes with ketones using carbon monoxide as a reducing agent. The procedure is suitable for the broad substrate scope, and a probable explanation for the fluoride role was provided.