fun: The synthetic potential of the highly regio‐ and stereoselective title reaction, which relies on two oxidativecleavage steps promoted by RuCl3 in combination with NaIO4 (see example; Bz=benzoyl), was demonstrated with the synthesis of biologically active cis‐(2R,3S)‐3‐hydroxypipecolic acid from D‐glucose.
Iron(III) chloride hexahydrate promotes a cascade of transformations on a Petasis condensation product that sets up the right dihydropyran precursors of valuable Relenza congeners.
Vicinal Diboronates in High Enantiomeric Purity through Tandem Site-Selective NHC−Cu-Catalyzed Boron−Copper Additions to Terminal Alkynes
作者:Yunmi Lee、Hwanjong Jang、Amir H. Hoveyda
DOI:10.1021/ja9089928
日期:2009.12.30
A Cu-catalyzed protocol for conversion of terminal alkynes to enantiomerically enriched diboronates is reported. In a single vessel, a site-selective hydroboration of an alkyne leads to the corresponding terminal vinylboronate, which undergoes a second site-selective and enantioselective hydroboration. Reactions proceed in the presence of 2 equiv of commercially available bis(pinacolato)diboron [B-2(pin)(2)] and 5-7.5 mol % loading of a chiral bidentate imidazolinium salt, affording diboronates in 60-93% yield and up to 97.5:2.5 enantiomeric ratio (er). The enantiomerically enriched products can be functionalized to afford an assortment of versatile organic molecules. Enynes are converted to unsaturated diboronates with high chemo- (>98% reaction of alkyne; <2% at alkene) and enantioselectivity (e.g., 94.5:5.5 er).