Without protection: α‐Keto aziridines have been formed in a novel amine‐promoted direct aziridination of chalcones using an aminimide generated in situ from a tertiary amine and O‐mesitylenesulfonylhydroxylamine (MSH) in the presence of base (see scheme). The aziridination proceeds well using a catalytic amount of the tertiary amine. Furthermore, nonracemic aziridines are obtained using a chiral amine.
An L-fructose-derived ketone catalyst for asymmetric epoxidation of trans- and trisubstituted olefins was efficiently prepared from L-sorbose in five steps.
Various 1,1-disubstituted terminal olefins have been investigated for asymmetric epoxidation using chiral ketone catalysts. Up to 88% ee has been achieved with a lactam ketone, and a planar transition state is likely to be a major reaction pathway.
The synthesis, conformational structure, electronic property, and anion complexation of novel coronarenes were systematically studied. A number of corona[4]arene[2]tetrazines that contain different combinations of nitrogen atoms with O, S, SO, and CH as bridging units were synthesized conveniently by means of a fragment coupling strategy based on efficient nucleophilic aromatic substitution reaction of easily available aromatic dinucleophiles and 3,6-dichlorotetrazine. The resulting macrocycles adopt crownlike conformational structures with the nitrogen bridge(s) forming conjugation with carbonyl and the other heteroatom linkages with tetrazine. CV and DPV measurements showed that the tetrazine-bearing coronarenes were electron deficient with reduction potentials ranging from -896 to -960 mV. Owing mainly to noncovalent anion-π attractive interactions, N,O-corona[4]arene[2]tetrazine formed complexes with anions of varied geometries and shapes yielding diverse assembled structures in the solid state.
Axially chiral BINIM-Ni(II) complexes are effective catalysts in the asymmetric 1,3-dipolar cycloaddition reactions of azomethine ylides and N-arylmaleimides to give the corresponding adducts in good yields and up to 95% enantiomeric excesses.
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