Photochemical reactions as key steps in natural product synthesis.

Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.