A Study of Exocyclic Radical Reductions of Polysubstituted Tetrahydropyrans
摘要:
Exocyclic radical reductions were thoroughly investigated in the context of the synthesis of polysubstituted tetrahydropyrans, Which are found in numerous macrolides. The radical precursors studied herein were generated by tandem cycloetherification and iodoetherification reactions or, alternatively, by semicyclic acetals substitutions. DFT calculations (BHandHLYP/TZVP) performed at the transition-state level for the hydrogen radical delivery are in good accordance with the experimental data and enabled the identification of important conformational factors that govern the selectivities obtained. This study demonstrates:that both the preferred reactive conformation of the radical and steric interactions with the incoming hydride have to be considered in order to fully rationalize the levels of diastereoselection generated in acyclic free-radical processes.
An improved synthesis of (−)-brevisamide, a marine monocyclic ether amide of dinoflagellate origin
作者:Ryosuke Tsutsumi、Takefumi Kuranaga、Jeffrey L.C. Wright、Daniel G. Baden、Emiko Ito、Masayuki Satake、Kazuo Tachibana
DOI:10.1016/j.tet.2010.06.074
日期:2010.8
An improved synthesis of (−)-brevisamide a marine cyclic ether isolated from the red-tide dinoflagellate Karenia brevis was achieved. The ether ring portion was constructed from an unsaturated lactone, which was prepared enantioselectively via an Evans aldol reaction and one-pot lactonization in the presence of excessive base after an Ando reaction. The ether ring and a dienol side chain fragment were