An Overview of the Total Synthesis of Pyrrolizidine Alkaloids via [4 + 1]Azide-Diene Annulation Methodology

All articles of this category The design and the execution of a multi-generation approach to pyrrolizidine alkaloids is summarized. A historical perspective and the various solutions to the problems of regio-, stereo-, and enantiocontrol in the preparation of these ubiquitous natural products are provided. The details of the fourth generation approach based on the resolution of ß-oxo esters of prochiral alcohols by yeast are disclosed. As this particular approach did not (we think) lead to optically pure products, a fifth-generation solution to the problems that were encountered is proposed. 1. Introduction 2. Historical Perspective 3. Regiochemistry of the [4 + 1] Intramolecular Pyrroline Annulation 4. Stereochemical Control in the Pyrrolizidine Diol Series 5. Enantiocontrolled Approach to Pyrrolizidine Triols 6. Attempted Enantiocontrolled Approach to Pyrrolizidine Diols 7. Conclusion