Sodium bicarbonate-catalyzed stereoselective isomerizations of electron-deficient propargylic alcohols to (Z)-enones

Redox isomerization is a synthetically important process because it creates two new functional groups in the product, among which is the isomerization of propargylic alcohols to conjugated enones. Although E-enones have been prepared by this approach, Z-enones could not be accessed. We previously reported DABCO-catalyzed E-selective isomerization of electron-deficient propargylic alcohols to enones and its mechanism. Based on this mechanism, we have now developed the first Z-selective redox isomerization of electron-deficient propargylic alcohol to enone using sodium bicarbonate as a catalyst.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Base-catalyzed stereoselective isomerization of electron-deficient propargylic alcohols to E-enones

We have developed highly stereoselective methods to isomerize electron-deficient propargylic alcohols to E-enones under mild conditions (EWG = electron-withdrawing group). Among weak bases we screened, catalytic (10-20 mol %) 1,4-diazabicyclo[2.2.2]octane (DABCO) was found to be effective in most cases. When the substrate is conjugated with an amide, the addition of sodium acetate catalyzed the isomerization.     

On the mechanism of DABCO-catalyzed isomerization of gamma-hydroxy-alpha,beta-alkynoates to gamma-oxo-alpha,beta-(E)-alkenoates

[reaction: see text] Since the discovery of organic base-catalyzed isomerization of gamma-hydroxy-alpha,beta-acetylenic esters to gamma-oxo-alpha,beta-trans-alkenyl esters in 1949, the mechanism has not been elucidated. This study shows that the mechanism involves cumulene formation, protonation with the conjugate acid of the amine, and protonation of the resulting allenol with water.     

Two connected inverse spectral transforms

We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems.