Stereospecific consecutive epoxide ring expansion with dimethylsulfoxonium methylide
Figure presented. Consecutive ring-expansion reactions of oxiranes with dimethylsulfxonium methylide were studied experimentally and modeled computationally at the density functional theory (DFT) and second-order Moller-Plesset (MP2) levels of theory utilizing a polarizable continuum model (PCM) to account for solvent effects. While the epoxide to oxetane ring expansion requires 13-17 kcal mol-1 activation and occurs at elevated temperatures, the barriers for the ring expansions to oxolanes are higher (ca. 25 kcal mol-1) and require heating to 125 °C. Further expansions of these oxolanes to the six-membered oxanes are hampered by high barriers (ca. 40 kcal mol-1). We observe the complete conservation of the enantiomeric purities for the nucleophilic ring expansions of enantiomeric 2-mono- and 2,2-disubstituted epoxides and oxetanes with dimethylsulfoxonium methylide. This is a convenient general approach for the high-yielding preparation of optically active four- and five-membered cyclic ethers from oxiranes.
Butova, Ekaterina D.,Barabash, Anastasiya V.,Petrova, Anna A.,Kleiner, Christian M.,Schreiner, Peter R.,Fokin, Andrey A.
experimental part
p. 6229 - 6235
(2010/11/18)
Asymmetric Synthesis of 2-Aryl Substituted Oxetanes by Enantioselective Reduction of β-Halogenoketones using Lithium Borohydride modified with N,N'-Dibenzoylcystine
Optically active 2-aryl substituted oxetanes are synthesised in high enantiomeric excesses (up to 89percent e.e.) via enantioselective reduction of β-halogenoketones with lithium borohydride using (R,R')-N,N'-dibenzoylcystine and t-butyl alcohols as ligands.