Pyrrolidines as Chiral Auxiliaries
Despite the fact that various enantioselective catalytic reactions are available for many important stereoselective reactions, diastereoselective auxiliary-controlled synthesis is still an important area of organic synthesis. Chiral pyrrolidine auxiliarie
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Pyrrolidines as Chiral Auxiliaries Wolfgang Maison
Contents 1 Introduction 2 Pyrrolidine Auxiliaries in α-Alkylation Reactions 3 Pyrrolidine Auxiliaries in Aldol Reactions 4 Pyrrolidine Auxiliaries in Michael Reactions 5 Pyrrolidine Auxiliaries in Rearrangements 6 Pyrrolidine Auxiliaries in Nucleophilic Additions to C¼N Bonds 7 Pyrrolidine Auxiliaries in Cycloadditions 8 Pyrrolidine Auxiliaries in Birch Reductions 9 Pyrrolidine Auxiliaries in Organometallic Chemistry 10 Miscellaneous Applications of Pyrrolidine Auxiliaries References
Abstract Despite the fact that various enantioselective catalytic reactions are available for many important stereoselective reactions, diastereoselective auxiliarycontrolled synthesis is still an important area of organic synthesis. Chiral pyrrolidine auxiliaries are frequently used in this context, due to good availability and efficient transfer of chirality via the rigid pyrrolidine scaffold. The following chapter focusses on recent examples and gives a brief overview of applications of pyrrolidine auxiliaries in diastereoselective syntheses. Illustrative examples were chosen to spotlight the underlying principles. Keywords Diastereoselective synthesis · Proline · Prolinol · Pyrrolidine auxiliaries · Traceless auxiliaries
W. Maison (*) Department of Chemistry, University of Hamburg, Hamburg, Germany e-mail: [email protected]
W. Maison
1 Introduction Chiral pyrrolidines are used frequently in asymmetric synthesis: as ligands and catalysts in catalytic stereoselective reactions, as structural motif in ex-chiral pool syntheses and as chiral auxiliaries in diastereoselective reactions. One of the major reasons for their frequent use in asymmetric synthesis is the good availability of many chiral derivatives either directly from the chiral pool of natural products or via easy preparation from readily available precursors such as proline and other amino acids. Another important factor is the rigidity of their cyclic pyrrolidine scaffold, which often allows an efficient transfer of chiral information to an attached substrate. The most prominent examples of pyrrolidine auxiliaries are depicted in Fig. 1. The first applications of proline esters as chiral auxiliaries via enamine derivatives date back to the work of Yamada et al. in the late 1960s [1]. Next to other chiral auxiliaries highlighted in this book, such as amino acid auxiliaries [2] and carbohydrate auxiliaries (Chapter “Heterocyclic Chiral Auxiliaries in Total Synthesis of Natural Products”), terpene derived auxiliaries (Chapter “Heterocyclic Chiral Auxiliaries in Total Synthesis of Natural Products”), oxazolidinones (Chapter “Heterocyclic Chiral Auxiliaries in Total Synthesis of Natural Products”) and boron containing auxiliaries, they belong to the most powerful tools in diastereoselective synthesis. The derivatives mentioned above fulfil the most important criteria for a successful auxiliary: cheap and straightforward synthesis, easy conjugation to substrates, efficient transfer of chiral information and mild cleav
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