Thieme Chemistry Journal Awardees - Where Are They Now? Stereoselective Synthesis of Z-Configured α,β-Unsaturated Macrocyclic Lactones and Diolides by Intramolecular Julia-Kocienski Olefination
acid with either ω-alkenols or α,ω-diols, followed by ozonolysis or Dess―Martin oxidation as appropriate, underwent intramolecular Julia―Kocienski olefination when treated with DBU. Macrocyclic α,β-unsaturated lactones of between 12- and 19-membered ringsizes were formed successfully using this tactic (24―44% yield, Z/E ≥ 3.5:1); however, diolides were selectively produced from precursors intended
Kumulierte Ylide XX.<sup>1</sup>Synthesen (<i>E</i>)-α,β-ungesättigter macrocyclischer Lactone durch intramolekulare Wittig-Olefinierung via Triphenylphosphoranylidenketen<sup>2</sup>
作者:Hans Jürgen Bestmann、Rainer Schobert
DOI:10.1055/s-1989-27271
日期:——
Cumulated Ylides XX.1 Syntheses of (E)-α,β-Unsaturated Macrocyclic Lactones by Intramolecular Wittig-Olefination via Triphenylphosphoranylideneketene2 Two methods for closure of macrocyclic lactone rings by intramolecular Wittig reaction of (Ï-oxoalkoxy)carbonylmethylenetriphenylphosphoranes are described. The latter are easily accessible by addition of the appropriate (free or protected) Ï-hydroxyalkanals to the cumulated ylide triphenylphosphoranylideneketene. Examples are then given for the use of these methods in natural product synthesis.
When the substrates (ArO)(2)P(O)CH2CO2-CHO (Ar = Ph, o-t-BuPh) were added to a THF solution containing 3 equiv of NaH at 0 degrees C or NaI-DBU at rt over 1-10 h, the Intramolecular Horner-Wadsworth-Emmons reaction proceeded efficiently to give the 12-18-membered-ring lactones in 69-93% yields with 89-100% Z selectivity. On the other hand, (EtO)(2)P(O)CH2CO2-CHO gave the 13-18-membered-ring lactones in 52-82% yields with 89-99% E selectivity using LiCl-DBU in MeCN or THF.