ABSTRACT
Photochemical reactions are characterized by the transformation of electronically excited molecules that are generated by light absorption.1,2 Compared to their ground state, such excited molecules possess completely dierent electronic congurations. Consequently, their chemical reactivity completely changes. Frequently, complementary reactions are observed for molecules at the ground and the excited states.3 us, using photochemical reactions, the spectrum of chemical transformations of a compound family is signicantly enlarged. Total syntheses can be shortened, and frequently complex, polycyclic, or highly functionalized structures can easily be obtained from simple substrates.4 New product families or product libraries di‚cult to achieve with ground-state reactions are thus available, opening new perspectives in the search of biologically active compounds. Catalytic reactions are also aected by light irradiation. Either ground-state reactions become more e‚cient or new catalytic reactions are observed. Such reactions also enrich the methodology in organic synthesis. A†er a period of stagnation, activity in the eld of organic photochemical reactions and their application to synthesis has started to grow again in academic and industrial research. In the two preceding editions of this handbook5 as well as in other books,1,6,7 large collections of organic photochemical reactions are presented. Many books deal with experimental conditions and equipment.1,8 is chapter brie‘y discusses some selected examples predominantly chosen in the eld of total synthesis and synthesis of biologically active compounds. e examples have been manly taken from recent literature.
