Coumarins and their derivatives are important classes of heterocyclic compounds whose synthesis has been the focus of attention of many organic and medicinal chemists. Such an interest in these compounds can be attributed to their variety of bioactivities such as, inhibition of platelet aggregation [1], antibacterial [2], anticancer [3], inhibitor of steroid 5αreductase [4] and inhibitor of HIV...

a mild and efficient method has been developed for the preparation of substituted coumarins from reaction of various phenols with different β-ketoesters via pechmann condensation in the presence of brønsted acidic ionic liquid (n-(4-sulfonic acid) butyl triethylammonium hydrogen sulfate) as an effective catalyst under solvent-free conditions. different phenols reacted with ethyl acetoacetate to...

A mild and efficient method has been developed for the preparation of substituted coumarins from reaction of various phenols with different β-ketoesters via Pechmann condensation in the presence of Brønsted acidic ionic liquid (N-(4-sulfonic acid) butyl triethylammonium hydrogen sulfate) as an effective catalyst under solvent-free conditions. Different phenols reacted with ethyl acetoacetate to...

A mild and efficient method has been developed for the preparation of substituted coumarins from reaction of various phenols with different β-ketoesters via Pechmann condensation in the presence of Brønsted acidic ionic liquid (N-(4-sulfonic acid) butyl triethylammonium hydrogen sulfate) as an effective catalyst under solvent-free conditions. Different phenols reacted with ethyl acetoacetate to...

The red Pechmann dye (λ(max) = 550 nm) is the exo-dimer of 4-phenyl-3-butenolide connected at the α-carbon by a double bond in a trans-fashion. The ring system is easily rearranged to the trans-endo-fused bicyclic 6-membered lactone dimer (yellow). Both lactones can be singly or doubly amidated with primary amines leading to further colour changes. The nature of the core heterocycle (exo- vs. e...

We consider the Dirichlet eigenvalues of Laplacian among a Poissonian cloud hard spherical obstacles fixed radius in large boxes $\mathbb{R}^d$, $d \ge 2$. In box side-length $2l$ centered at origin, lowest eigenvalue is known to be typically order $(\log l)^{-2/d}$. show here that with probability arbitrarily close $1$ as $l$ goes infinity, spectral gap stays bigger than $\sigma (\log l)^{-(1 ...