Stereoselektive Protonierung von Carbanionen, 3. 1,3‐Dioxolan‐4‐one und 1,3‐Oxazolidin‐4‐one: Synthesen und diastereoselektive Protonierung ihrer Anionen

Stereoselective Protonation of Carbanions, 3. — 1,3‐Dioxolan‐4‐ones and 1,3‐Oxazolidine‐4‐ones: Syntheses and Diaste‐reoselective Protonation of their Anions Dioxolonanones 3 and oxazolidinones 4 are synthesized by different methods together with the silyl enol ether 3asi. The configuration of their diastereomers is determined by 1H‐NMR spectroscopy and relative retention times (vpc), backed by a crystal structure analysis of cis‐3d. Protonation of 3aLi and 4aLi by different OH and CH proton sources in THF at ‐78°C occurs by kinetic product control yielding always ca. 70–90% of the cis isomers. Exchange of the cation in 3Li by potassium or addition of several Lewis acids does not effect the cis/trans relations. Obviously, even the steric effect of a methyl group in 2‐position of 3Li and 4Li dominates so strongly that the effect of other parameters are suppressed.