Strategies to Control Alkoxy Radical-Initiated Relay Cyclizations for the Synthesis of Oxygenated Tetrahydrofuran Motifs
摘要:
Radical relay cyclizations initiated by alkoxy radicals are a powerful tool for the rapid construction of substituted tetrahydrofurans. The scope of these relay cyclizations has been dramatically increased with the development of two strategies that utilize an oxygen atom in the substrate to accelerate the desired hydrogen atom transfer (HAT) over competing pathways. This has enabled a chemoselective 1,6-HAT over a competing 1,5-HAT. Furthermore, this allows for a chemoselective 1,5-HAT over competing direct cyclizations and beta-fragmentations. Oxygen atom incorporation leads to a general increase in cyclization diastereoselectivity over carbon analogues. This chemoselective relay cyclization strategy was utilized in the improved synthesis of the tetrahydrofuran fragment in (-)-amphidinolide K.
A Ring‐Closing Metathesis Approach to Cyclic α,β‐Dehydroamino Acids
作者:Koen F. W. Hekking、Dennis C. J. Waalboer、Marcel A. H. Moelands、Floris L. van Delft、Floris P. J. T. Rutjes
DOI:10.1002/adsc.200700308
日期:2008.1.4
the synthesis and ring-closingmetathesis (RCM) of α,β-dehydroamino acids is described. This sequence has led to the formation of a range of biologically relevant functionalized nitrogen heterocycles. The incorporation of chiral building blocks in the RCM precursors eventually resulted in the formation of optically active 4-substituted cyclic dehydroamino acids. In addition, olefin isomerization under