Enantioselective Synthesis of α,β-Disubstituted-β-amino Acids
摘要:
Highly diastereoselective and enantioselective addition of N-benzylhydroxylamine to imides 17 and 20-30 produces alpha,beta-trans-disubstituted N-benzylisoxazolidinones 19 and 31-41. These reactions proceed in 60-96% ee with 93-99% de's using 5 mol % of Mg(NTf2)2 and ligand 18. The product isoxazolidinones can be hydrogenolyzed directly to provide alpha,beta-disubstituted-beta-amino acids.
Enantioselective Enolate Protonation in Sulfa–Michael Addition to α-Substituted <i>N</i>-Acryloyloxazolidin-2-ones with Bifunctional Organocatalyst
作者:Nirmal K. Rana、Vinod K. Singh
DOI:10.1021/ol202808n
日期:2011.12.16
Organocatalytic conjugate addition of thiols to α-substituted N-acryloyloxazolidin-2-ones followed by asymmetric protonation has been studied in the presence of cinchona alkaloid derived thioureas. Both of the enantiomers are accessible with the same level of enantioselectivity using pseudoenantiomeric quinine/quinidine derived catalysts. The addition/protonation products have been converted to useful biologically
Conjugate addition of allylsilanes to α,β-unsaturated N-acyloxazolidinones
作者:Ming-Jung Wu、Jiann-Yih Yeh
DOI:10.1016/s0040-4020(01)80818-8
日期:1994.1
The conjugate addition of allyltrimethylsilane to alpha,beta-unsaturated N-acyloxazolidinone at -78 degrees C in the presence of TiCl4 gave the allylation product 3. However, when the reaction was carded out at room temperature, a small amount of cyclopentane adduct 4 was observed. The cyclopentane product formation can be prevented by employing BF3.OEt(2) as a Lewis acid. The enantioselective synthesis of optically pure 3-substituted-5-hexenoic acids was achieved by employing chiral oxazolidinone as a chiral auxiliary.
Stereospecific nucleophilic addition reactions to olefins. Addition of thiols to .alpha.,.beta.-unsaturated carboxylic acid derivatives
Stereospecific nucleophilic addition of thiols to derivatives of alpha,beta-unsaturated carboxylic acids is described. The additions are carried out at room temperature in the presence of a catalytic amount of lithium thiolate and an excess of thiol as a proton source. Erythro and threo adducts are obtained with high diasteroselectivity from E and Z olefins, respectively. This anti addition suggests that the enolate generated by nucleophilic addition undergoes rapid protonation prior to conformational change in the intermediate.
Synthesis of (±)-Nosyberkol (Isotuberculosinol, Revised Structure of Edaxadiene) and (±)-Tuberculosinol
作者:Nathan Maugel、Francis M. Mann、Matthew L. Hillwig、Reuben J. Peters、Barry B. Snider
DOI:10.1021/ol100832h
日期:2010.6.4
Me(2)AlCl-catalyzed Diels-Alder reaction of N-tigloyloxazolidinone with 6,6-dimethyl-1-vinylcyclohexene selectively provided the exo adduct, which was converted to nosyberkol (isotuberculosinol) and tuberculosinol. The spectral data for nosyberkol are identical with those reported for edaxadiene, whose structure is revised accordingly.