STEREOSELECTIVE PROTONATION OF CARBANIONS .3. 1,3-DIOXOLAN-4-ONES AND1,3-OXAZOLIDINE-4-ONES - SYNTHESES AND DIASTEREOSELECTIVE PROTONATIONOF THEIR ANIONS

Dioxolonanones 3 and oxazolidinones 4 are synthesized by different met hods together with the silyl enol ether 3a(Si). The configuration of t heir diastereomers is determined by H-1-NMR spectroscopy and relative retention times (vpc), backed by a crystal structure analysis of cis-3 d. Protonation of 3aLi and 4aLi by different OH and CH proton sources in THF at -78-degrees-C occurs by kinetic product control yielding alw ays ca. 70-90% of the cis isomers. Exchange of the cation in 3Li by po tassium or addition of several Lewis acids does not effect the cis/tra ns relations. Obviously, even the steric effect Of d methyl group in 2 -position of 3Li and 4Li dominates so strongly that the effect of othe r parameters are suppressed.