Cobalt Phenanthroline–Indole Macrocycles as Highly Active Electrocatalysts for Oxygen Reduction

The replacement of scarce and expensive platinum species poses a challenge in fuel‐cell development. The design and synthesis of a novel type of Co^II–N₄ macrocyclic complex, [CoN₄], based on the phenanthroline–indole macrocyclic ligand (PIM) is reported. This unique ligand allows the formation of mono‐ and dinuclear complexes with defined active sites that facilitate the direct four‐electron reduction of oxygen. Electrochemical measurements revealed that the [CoN₄]/C (20 wt %) catalysts have a high activity and long‐term stability for the oxygen‐reduction reaction (ORR) under alkaline conditions, similar to the Pt/C catalyst. These structurally well‐defined complexes represent a nonprecious alternative to platinum species for future fuel‐cell applications.     

Discovery and Application of Doubly Quaternized Cinchona‐Alkaloid‐Based Phase‐Transfer Catalysts

We report the discovery of novel N,N′‐disubstituted cinchona alkaloids as efficient phase‐transfer catalysts for the assembly of stereogenic quaternary centers. In comparison to traditional cinchona‐alkaloid‐based phase‐transfer catalysts, these new catalysts afford substantial improvements in enantioselectivity and reaction rate for intramolecular spirocyclization reactions with catalyst loadings as low as 0.3 mol % under mild conditions.     

Intermolecular cycloaddition of N-boranonitrone with alkenes

Ethyl glyoxylate O-tert-butyldimethylsilyloxime (8), on treatment with 2.2 equiv of BF3 x OEt2, generated N-boranonitrone E, which underwent intermolecular cycloaddition with alkenes 18 to afford isoxazolidines 19 in moderate to high yields. The cycloaddition of N-boranonitrone E with most of the alkenes gave 3,5-trans isoxazolidines as the major isomers via a concerted mechanism. However, in the case of 1-methylated cyclic alkenes (18j and 18l), the cycloaddition surprisingly furnished the 3,3a-cis-cycloadducts (19j and 19l) as major isomers. A possible explanation is that the reaction of 1-methylated cyclic alkenes proceeds mainly via a stepwise mechanism. This reaction of terminal alkenes is very useful for synthesis of 1,3-anti aminoalcohol derivatives by reductive cleavage of an N-O bond.