Asymmetric autocatalysis and the origin of chiral homogeneity in organic compounds

The discovery and development of asymmetric autocatalysis, in which the structures of the chiral catalyst and the chiral product are the same, are described. Chiral 5-pyrimidyl, 3-quinolyl, and 5-carbamoyl-3-pyridyl alkanols act as highly enantioselective asymmetric autocatalysts in the enantioselective addition of diisopropylzinc to the corresponding aldehydes, such as pyrimidine-5-carbaldehyde. 2-Alkynyl-5-pyrimidyl alkanol with an enantiomeric excess (ee) of >99.5% automultiplies practically perfectly as an asymmetric autocatalyst in a yield of >99% and >99.5% ee. Asymmetric autocatalysis with an amplification of ee has thus been realized. Consecutive asymmetric autocatalysis starting with chiral 2-alkynylpyrimidyl alkanol of only 0.6% ee amplifies its ee significantly, and yields itself as the product with >99.5% ee. The reaction of pyrimidine-5-carbaldehyde and diisopropylzinc in the presence of chiral initiators with low ee's, such as secondary alcohol, amine, carboxylic acid, mono-substituted [2.2]paracyclophane, and chiral primary alcohols due to deuterium substitution, regulates the absolute configuration of the resulting pyrimidyl alkanols, and the ee of the resulting pyrimidyl alkanol is much higher than that of the chiral initiator. Leucine and [6]helicene with very low ee's, which are known to be induced by circularly polarized light (CPL), also serve as chiral initiators to produce pyrimidyl alkanol with higher ee's. Overall, the process represents the first correlation between the chirality of CPL and an organic compound with very high ee. Chiral inorganic crystals, such as quartz and sodium chlorate, act as chiral inducers in the asymmetric autocatalysis of pyrimidyl alkanol. The process correlates for the first time ever the chirality of inorganic crystals with an organic compound with very high ee.     

The effect of iodide on the electrochemical reduction of thick oxide films formed on platinum electrodes in sulfuric acid solution

The reduction of thick oxide films formed on Pt under severe anodic conditions was studied in the presence of adsorbed I^?. The Pt electrode covered with a thick oxide film does not adsorb I^?. However, when a superficial monolayer oxide on the thick oxide has been reduced, I^? is irreversibly adsorbed. Iodide adsorbed on its surface blocks the adsorption of hydrogen and retards markedly the cathodic reduction of the inner thick oxide remaining. It was found that the reduction rate of the inner oxide depends only on the coverage by hydrogen, which coexists with adsorbed I^?. These results support the proton-electron theory which has previously been proposed for the explanation of the characteristic reduction of the thick oxide films.     

Determination of carbon isotope ratios of methanol and acetaldehyde in air samples by gas chromatography-isotope ratio mass spectrometry combined with headspace solid-phase microextraction

Isotopic signatures of atmospheric methanol and acetaldehyde have the potential to improve our ability to quantitatively assess their importance in atmospheric chemistry. However, isotopic measurements of atmospheric methanol and acetaldehyde and their individual source and sink processes have been limited. In this study, we examined gas chromatography-isotope ratio mass spectrometry combined with headspace solid-phase microextraction to measure the carbon isotope ratios of methanol and acetaldehyde in air samples. The method enabled us to determine carbon isotope ratios with a precision (1 standard deviation) of±0.6 ‰ for 20 ml of air sample containing more than 3 ppm of methanol and±0.7 ‰ for 20 ml of air sample containing more than 2 ppm of acetaldehyde. Moreover, the applicability of this method to determine isotope ratios of methanol and acetaldehyde emitted from detached plant leaves was demonstrated.     

Highly Chemo‐, Enantio‐, and Regioselective Synthesis of α,α‐Disubstituted Furanones by Cu‐Catalyzed Conjugate Addition

A highly chemo‐, enantio‐, and regioselective synthesis of furanones bearing an α,α‐disubstituted quaternary stereogenic center is reported. The Cu‐catalyzed enantioselective conjugate addition of organoaluminum reagents to unsaturated ketoesters at room temperature and subsequent lactonization took place. Synthetic transformations of furanones represent facile approaches to various cyclic or acyclic compounds bearing a quaternary stereogenic center.