was used in phase-transfer alkylations and Michael additions to afford various opticallyactive α-amino acid equivalents in up to 93% yield. Moreover, dramatic counter anion effects were observed in phase-transfer catalysis (PTC) for the first time, making it possible to further improve reactivity and selectivity. These findings validate the usefulness of three-dimensional fine-tuning of the catalyst
Thermochemical studies of carbonyl reactions. 2. Steric effects in acetal and ketal hydrolysis
作者:Kenneth B. Wiberg、Robert R. Squires
DOI:10.1021/ja00405a030
日期:1981.7
series of alkyl-substituted dimethyl acetals is reported. These data are critially compared with the enthalpies of hydrolysis from an analogous set of aliphatic dimethyl ketals derived from 2-alkanones. The acetals exhibit a significantly attenuated range in their enthalpies of hydrolysis relative to that for ketal hydrolysis. The free energies of acetalformation in solution were modeled by measurements
Thermodynamics of hydrolysis of aliphatic ketals. An entropy component of steric effects
作者:Kenneth B. Wiberg、Robert R. Squires
DOI:10.1021/ja00513a009
日期:1979.9
The enthalpies and free energies of the acid-catalyzed hydrolysis of a series of a alkyl-substituted dimethyl ketals have been determined in a model study of steric effects. The measured enthalpy differences did not correlate with standardquantitative notions of the steric bulk of the substituents, although the overall free-energy changes fit the expected order. The entropy effect of the substituents
Trifluoroacetylation of unsymmetrical ketone acetals. A convenient route to obtain alkyl side chain trifluoromethylated heterocycles
作者:Helio G Bonacorso、Marcos A.P Martins、Sandra R.T Bittencourt、Rogério V Lourega、Nilo Zanatta、Alex F.C Flores
DOI:10.1016/s0022-1139(99)00146-3
日期:1999.11
A convenient method to obtain β-alkyl-β-methoxyvinyl trifluoromethyl ketones [CF3COCHC(OMe)R, where R = Et, n-Pr, i-Pr, i-Bu, t-Bu, –(CH2)2OMe] from the regiospecific acylation of kinetic enol ether generated in situ is reported. The unsymmetrical ketone dimethyl acetals react with trifluoroacetic anhydride in the presence of pyridine using dry chloroform as solvent with a temperature range of 25–60°C