The asymmetric synthesis of enantiomerically pure a-substituted tertiary homoallylic ethers 4a, 11 and 12a-c by the allylation of ethyl methyl ketone (la) with gamma-substituted allylsilanes 9a-h is described. The allylsilanes were obtained by a nickel-catalysed Grignard cross-coupling reaction of (E)- and (Z)-(3-iodoallyl)trimethylsilane with various Grignardreagents. The reaction of the allylsilanes
Propargyltrimethylsilanes as Allene Equivalents in Transition Metal-Catalyzed [5 + 2] Cycloadditions
作者:Paul A. Wender、Fuyuhiko Inagaki、Magnus Pfaffenbach、Matthew C. Stevens
DOI:10.1021/ol501114q
日期:2014.6.6
including metal-catalyzed [5 + 2] cycloadditions. We report herein that rhodium-catalyzed [5 + 2] cycloadditions of propargyltrimethylsilanes and vinylcyclopropanes provide, after in situ protodesilylation, a highly efficient route to formal allene cycloadducts. Propargyltrimethylsilanes function as safe, easily handled synthetic equivalents of gaseous allenes and hard-to-access monosubstituted allenes
Chiral titaniumcomplex (1), prepared in situ from optically pure binaphthol and diisopropoxytitanium dihalide in the presence of molecular sieves, is shown to catalyze the additionreactions of crotylsilanes and -stannanes to glyoxylates to afford (syn)-α-hydroxy-β-methyl esters in highly scalemic forms with high diastereoselectivity.
Rhodium-Catalyzed Arylzincation of Alkynes: Ligand Control of 1,4-Migration Selectivity
作者:Jialin Ming、Tamio Hayashi
DOI:10.1021/acs.orglett.8b02668
日期:2018.10.5
The addition of arylzinc reagents ArZnCl 1 to alkynes 2 was found to be catalyzed by rhodium complexes in the presence of a catalytic amount of zinc chloride. The selectivity in giving 2-arylalkenylzinc species 3 or ortho-alkenylarylzinc species 4, the latter of which is generated through 1,4-Rh migration from alkenyl to aryl in the catalytic cycle, is controlled by the ligands on rhodium. Ligands
gel-supported sodium hydrogen sulfate (NaHSO4/SiO2) or Amberlyst 15 as solid acid catalyst, and then the corresponding 3-acylisoxaszoles were obtained by reacting with alkynes via the 1,3-dipolar [3+2] cycloaddition. These heterogeneous catalysts are easily separable from the reaction mixture and reused. This synthetic method provides a facile, efficient, and reusable production of 3-acylisoxazoles.