Studies toward the synthesis of the guaianolide skeleton: an intramolecular hetero Diels Alder approach and a carbonyl ene approach

This thesis describes the efforts towards the synthesis of the guaiane-6,12-olide skeleton, which characterises the guaianolide family of bioactive natural compounds. Two approaches have been investigated: the intramolecular hetero Diels Alder (IMHDA) reaction and the intramolecular carbonyl ene reaction. This thesis has been divided in three sections: the first part gives a general background about the guaianolides, the second section describes the synthetic approaches we investigated and, finally, the third section reports the experimental details. The first section gives a brief overview about the biosynthesis, the biological activities of the guaianolides, and the most interesting synthetic approaches to obtain them. The second section describes the two different approaches we investigated and gives a theoretical background about the main chemical transformations used. At first, the IMHDA reaction approach is described: a brief overview of palladium catalysis and Diels Alder reaction is given, and it is followed by the results and discussion of our study. Similarly, a theoretical background of the Alder ene reaction is given, before the results and discussion of the intramolecular carbonyl ene reaction approach are described: particular importance is given to the reasoning that led to the assignment of the relative configuration of the cycloadducts obtained, and to the rationalisation of this stereochemical outcome. Finally, the third section gives a complete description of the experimental procedures followed, and of the experimental data for the synthetic studies performed in the previous chapter.