Abstract
Lewis acids have played pivotal role in organic synthesis. The inherent Lewis acidity of semi-metal or metal ions, which stems from possession of empty orbitals or electron-accepting ability/electron pair affinity, has granted them ability to catalyze various and numerous organic functional group transformations and methods for carbon-carbon (C-C) bond formation reactions. Lewis acids have developed from conventional catalysts to modern green ones that have enabled a wide range of chemical transformations and chemical processes of applications in various fields such as pharmaceutical and petroleum/petrochemical industries. The chapter begins with definition and description of Lewis acids and their significance in chemistry as an electronic science. The chapter then covers uses and applications of Lewis acids as homogeneous catalysts in conventional organic reactions that employ and/or are Lewis-acids catalysts. Coverage continues on the importance of developments and inception of green and environmentally benign Lewis acids that can help preserve the environment, in a manifestation of green chemistry principles. Illustrations of the importance and applications of green Lewis acids in Lewis acid-catalyzed organic reactions and C-C bond formation reactions are covered. The chapter aims at introducing and stimulating the reader to Lewis acids, their description and significance in synthetic organic chemistry in particular and in chemistry as a whole.