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Stereoselektive Protonierung von Carbanionen, 3. 1,3‐Dioxolan‐4‐one und 1,3‐Oxazolidin‐4‐one: Synthesen und diastereoselektive Protonierung ihrer Anionen
Author(s) -
Hünig Siegfried,
Keita Yango,
Peters Karl,
von Schnering HansGeorg
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941270824
Subject(s) - chemistry , protonation , carbanion , diastereomer , steric effects , lewis acids and bases , oxazolidine , medicinal chemistry , stereochemistry , intramolecular force , enol ether , silyl enol ether , nuclear magnetic resonance spectroscopy , ether , silylation , organic chemistry , catalysis , ion
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 3a si . The configuration of their diastereomers is determined by 1 H‐NMR spectroscopy and relative retention times (vpc), backed by a crystal structure analysis of cis ‐ 3d . Protonation of 3a Li and 4a Li 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 3 Li 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 3 Li and 4 Li dominates so strongly that the effect of other parameters are suppressed.