Eu(OTf)<sub>3</sub>-Catalyzed Highly Regioselective Nucleophilic Ring Opening of 2,3-Epoxy Alcohols: An Efficient Entry to 3-Substituted 1,2-Diol Derivatives
In our study of the totalsynthesis of (+)-irciniastatin A, we found a need to develop a method that enables a C3-selective nucleophilicringopening of 2,3-epoxyalcohol by MeOH, by which we found that the use of combined catalytic amounts of Eu(OTf)3 and 2,6-di-tert-butyl-4-methylpyridine (DTBMP) enables the intended transformation to obtain 3-methoxy-1,2-diol efficiently. Promising features of a
A new attempt of utilizing solid acids and bases for ring opening of epoxides with Me3SiCN was investigated. Solid strong bases such as calcium oxide and magnesium oxide catalyzed the regio- and chemoselective ring opening of epoxides with Me3SiCN much more effectively than homogeneous catalysts. On CaO and MgO, the reactions of unsymmetrical epoxides with Me3SiCN afforded 3-trimethylsiloxyalkanenitriles in high yields through regio- and stereoselective attack of cyanide ion on the less substituted epoxycarbon. Additionally, on CaO, 2,3-epoxy-1-alkanol derivatives were selectively converted to the corresponding C-3 opened products by the attack of cyanide ion. In these cases no isocyanides were formed. It was suggested that CaO acted as a bifunctional catalyst; the lattice oxide anions of CaO activated Me3SiCN, and simultaneously calcium ions promoted the ring opening of epoxyalkanol as Lewis acid sites.
Epoxidation of Olefins with a Silica-Supported Peracid
作者:Rossella Mello、Ana Alcalde-Aragonés、María Elena González Núñez、Gregorio Asensio
DOI:10.1021/jo300533b
日期:2012.8.3
Anhydrous [2-percarboxyethyl] functionalized silica (2a) is an advantageous oxidant for performing the epoxidation of olefins 1. Epoxides 3 do not undergo the ring-opening reactions catalyzed by the acidic silica surface, except for particularly activated cases such as styrene oxide. The hydrophilic and acidic character of the silica surface does not interfere with the directing effects exerted by
Epoxidation of Olefins with a Silica-Supported Peracid in Supercritical Carbon Dioxide under Flow Conditions
作者:Rossella Mello、Ana Alcalde-Aragonés、Andrea Olmos、María Elena González-Núñez、Gregorio Asensio
DOI:10.1021/jo300532f
日期:2012.5.18
2-percarboxyethyl-functionalized silica (2b), a recyclable supported peracid, is a suitable reagent to perform the epoxidation of alkenes 1 in supercriticalcarbondioxide at 250 bar and 40 °C underflowconditions. This procedure simplifies the isolation of the reaction products and uses only carbondioxide as a solvent under mild conditions. The solid reagent 2b can be easily recycled by a reaction with