Diels-Alder reactions and synthetic methodologies on alumina and study of LiClO4/ether system

The Diels-AIder reactions of dimethyl maleate, dimethyl fumarate, (-)-dimenthyl fumarate and (-)-menthyl methyl fumarate with cyclopentadiene on σ-Aumina and the Diels-Alder reactions of dimethyl maleate, (-)-dimenthyl fumarate and (-)-menthyl methyl fumarate with cyclopentadiene in LiClO₄/diethyl ether were examined. The diastereoselectivity of the Diels-Alder reactions increases with increasingly activated alumina. The diastereoselectivity for the Diels-Alder reactions carried out in LiClO₄/diethyl ether appears to be moderated due to complexation of the Li⁺ with ether and ClO₄^-. The Tolbert-Ali test was applied to the results of the Diels-Alder reactions of (-)- dimenthyl fumarate and (-)-menthyl methyl fumarate with cyclopentadiene which were carried out on alumina and in LiClO₄/diethyl ether. A chemical, spectroscopic, and theoretical investigation was carried out to determine the Lewis acidity of LiClO₄ in diethyl ether. The chemical investigation was done by carrying out the Diels-Alder reaction of dimethyl maleate, (-)-dimenthyl fumarate and (-)-menthyl methyl fumarate with cyclopentadiene in LiClO₄/diethyl ether. The spectroscopic investigation (¹H NMR) was carried out by complexing the Lewis acid with crotonaldehyde and measuring the induced chemical shift. The theoretical investigation was carried out using the MNDO calculations and measuring the extent of lowering of energy of the lowest unoccupied molecular Orbital (Lumo). The studies showed that the Li⁺ is a strong Lewis acid in the gas-phase but in solution its acidity is moderated due to complexation with ether and ClO₄^-.