0000000000555504
AUTHOR
Monika Buß
(Z)- und (E)-Enole von diarylsubstituierten β-Ketocarbonsäurederivativen
(Z) and (E) Enols of Diaryl-Substituted β-Ketocarboxylic Acid Derivatives Thermolysis of the 1,3-diaryl-2-diazo-1,3-propanediones 4 in the presence of alcohols or amines yielded the compounds 7–11 which exist as chelated (Z) enols or as tautomeric ketones. Contrary to the steric interaction of two mesityl groups the steric interaction between two naphthyl or two anthryl groups or between naphthyl and mesityl is not sufficient to stabilize the corresponding (E) enols. The latter isomers were generated in irradiation processes of some (Z) enols. Detailed NMR studies were performed in order to characterize the enols and their molecular dynamics.
Vergleichende Untersuchung zur Diastereoselektivität derO-Methylierung von sterisch behinderten β-Ketocarbonsäureestern und ihren Enolen
Diastereoselectivity of the O-Methylation of Sterically Hindered β-Ketocarboxylates and Their Enols The enols 1a, b, and 1c, which exists almost completely in the keto form, have been methylated at the oxygen atom with diazomethane. The regioselective reaction can be catalyzed by methanol, but may loose in that case the diastereoselectivity. A comparison with the methylation of the enolates by iodomethane is discussed.
Configuration of Enolates of β-Ketocarboxylic Acid Esters — Carbocation-Carbanion Salts
Deprotonation of (Z)- or (E)-3-hydroxy-2,3-dimesitylpropenoic acid methyl ester (1a) with tetrakis(dimethylamino)-methane (3) led to stable salt (E)-2a, which belongs to a very rare species of salts that consist of a heteroatom-stabilized carbocation and a heteroatom-stabilized carbanion. An analogous guanidinium salt (E)-2b was formed in the reaction of 3-oxo-2,3-diphenylpropanoic acid methyl ester (1b) and 3. The molecular structures of these enolates were studied by NMR spectroscopy and an X-ray analysis of (E)-2a {MC[N(CH3)2]3} and compared with those of the corresponding alkali enolates.