Influence of steric parameters on the synthesis of tetramates from α-amino-β-alkoxy-esters and Ph3PCCO
摘要:
alpha-Aminoesters react with Ph3PCCO in a domino addition-Wittig cyclization sequence affording enantiomerically pure tetramates. In the case of beta-oxo functionalized alpha-aminoesters, e.g., esters of serine, threonine or beta-hydroxyornithine the yields of this reaction depend heavily on the bulkiness of the beta-OR group and on the configuration of beta-carbon atom C-3. Smaller residues and 2R/3R-configured aminoesters give better yields. The alkoxycarbonyl group of the ester moiety and the residue on the N-atom are less important. These findings can be accounted for by assuming an early puckered transition state for the intramolecular ring-closing Wittig reaction. The addition of sub-stoichiometric amounts of benzoic acid or N-hydroxysuccinimide (for acid-sensitive compounds) is advantageous in some cases as it accelerates the formation of the intermediate amide ylides. (C) 2011 Elsevier Ltd. All rights reserved.
Influence of steric parameters on the synthesis of tetramates from α-amino-β-alkoxy-esters and Ph3PCCO
摘要:
alpha-Aminoesters react with Ph3PCCO in a domino addition-Wittig cyclization sequence affording enantiomerically pure tetramates. In the case of beta-oxo functionalized alpha-aminoesters, e.g., esters of serine, threonine or beta-hydroxyornithine the yields of this reaction depend heavily on the bulkiness of the beta-OR group and on the configuration of beta-carbon atom C-3. Smaller residues and 2R/3R-configured aminoesters give better yields. The alkoxycarbonyl group of the ester moiety and the residue on the N-atom are less important. These findings can be accounted for by assuming an early puckered transition state for the intramolecular ring-closing Wittig reaction. The addition of sub-stoichiometric amounts of benzoic acid or N-hydroxysuccinimide (for acid-sensitive compounds) is advantageous in some cases as it accelerates the formation of the intermediate amide ylides. (C) 2011 Elsevier Ltd. All rights reserved.
alpha-Aminoesters react with Ph3PCCO in a domino addition-Wittig cyclization sequence affording enantiomerically pure tetramates. In the case of beta-oxo functionalized alpha-aminoesters, e.g., esters of serine, threonine or beta-hydroxyornithine the yields of this reaction depend heavily on the bulkiness of the beta-OR group and on the configuration of beta-carbon atom C-3. Smaller residues and 2R/3R-configured aminoesters give better yields. The alkoxycarbonyl group of the ester moiety and the residue on the N-atom are less important. These findings can be accounted for by assuming an early puckered transition state for the intramolecular ring-closing Wittig reaction. The addition of sub-stoichiometric amounts of benzoic acid or N-hydroxysuccinimide (for acid-sensitive compounds) is advantageous in some cases as it accelerates the formation of the intermediate amide ylides. (C) 2011 Elsevier Ltd. All rights reserved.