الفهرس | Only 14 pages are availabe for public view |
Abstract 1.1. Aim of the work New asymmetric methods to generate the cyclopropane motif have attracted widespread attention from the synthetic community owing to their ubiquitous presence in a diverse range of natural products and their crucial role in the mode of action of many therapeutic agents. Furthermore, the rigid structure and strain-driven reactivity make them attractive intermediates in the synthesis of complex molecules. Because of these important properties and the need for efficient methods for their stereoselective formation, the synthesis of cyclopropane containing molecules has become a platform for the development of new asymmetric catalytic processes. In the last few years numerous metal-catalyzed and organocatalytic intermolecular cyclopropanation reactions have been reported that enable the generation of discrete three-membered ring systems with high diastereoselectivity. The cyclopropane ring is a constituent in more than 4000 isolated natural products and 100 biologically active agents. Thus the present work examines primarily the utility of organic catalysts such as (S)- proline (256), (S)-prolinol (257), (S)-(2)-(diphenyltrimethylsiloxymethyl)-pyrrolidine (258) and (S)-(2)-(diphenyltrimethylsiloxymethyl)-pyrrolidine.TfOH (259) in organocatalytic cyclopropanation reactions between a-methacrolein (260) and a- diazoacetic ester as well as a-diazophosphonates as shown below . |