Application of microwave irradiation and solid acid catalysts in environmental organic chemistry. Synthesis and reactivity of heterocycles

The microwaves are electromagnetic waves located between infrared and radiowaves. The first work about the use of microwaves in Chemistry was published in 1986 and since then until now there have been lots of papers on this subject.; One of the applications of this new technique has been in what is called Environmental Chemistry or commonly known as Green Chemistry. The basic principles of this chemistry are: (1) not to create waste products; (2) to design energy efficient processes.; In this way, the use of microwaves under solvent free conditions, permit to reduce the reaction times, to avoid the use of large volumes of solvents, to use recyclable solid supports and the use of these solids in solvent free conditions simplified the work-up procedures.; With these antecedents the objective of this thesis was to perform reactions that need very long reaction times and acid catalysts in order to reduce these times and to avoid the use of homogeneous catalysts commonly used. These catalysts were substituted for different clays, resins and silica modified with metals. All the reactions were performed under solvent free conditions.; Using this method we performed: (1) Synthesis of coumarine derivatives: This synthesis was carried out using the Peachman reaction and one modification of this reaction that utilises α,β-insaturated acids. (2) Synthesis of aromatic derivatives from furan cycloadducts: Using silicas modified with metals we performed the Diels-Alder reaction of 2,5-dimethilfurane and another furan derivatives with different dienophiles to obtain the furan cycloadducts and/or the aromatic derivatives. In order to understand better the mechanism of this reaction, theoretical studies were carried out using the method Hartree-Fock 3-21G*. (3) Synthesis of alanine derivatives: Silica-supported Lewis acids were useful catalysts under microwave irradiation for the synthesis of a range of alanine derivatives. By reaction of α-acetamidoacrylate with different heterocycles as fura, pyrrole, N-benzylpyrrole, indole, pyrazole or with 1,3,3-trihidroxybenzene and 1,3,5-trimetoxybenzene, several precursors were synthesised. (4) Synthesis of quinoxalines: One of the most interesting applications of microwaves to chemistry is the synthesis of radioisotopes because with this technique the reaction times are shorter and the yields bigger. In this chapter a method of synthesis of quinoxaline derivatives, for posterior PET analysis, was performed.