Steric limits to ester alkylation; synthesis of highly hindered esters via hexamethylphosphoramide-favoured enolization
作者:John Anthony MacPhee、Jacques-Emile Dubois
DOI:10.1039/p19770000694
日期:——
αα-disubstituted from α-monosubstituted esters takes place in high yields and appears to be only slightly influenced by the nature of the alkylating agent (Mel, Etl, or Pril). In contrast, the formation of ααα-trisubstituted for αα-disubstituted esters appears to be sensitive to the steric nature of the ester to be alkylated. Thus in the synthesis of tri-from mono-substituted esters the order of introduction of
在改良的情况下,已经通过使用Schlessinger等人最初提出的方法研究了在六甲基磷酰胺存在下,烷基碘化物以二异丙基氨基锂为碱,通过烷基碘化物使羧酸酯烷基化的空间极限。如前所述,已经研究了六甲基磷酰胺在促进酯烯化中的作用,与其对烷基化步骤的影响相反。由α-单取代酯形成αα-二取代酯的收率很高,而且似乎仅受烷基化剂性质的影响(Mel,Etl或Pr il)。相反,对于αα-二取代酯,形成αα-三取代的αα似乎对要烷基化的酯的空间性质敏感。因此,在三-单取代酯的合成中,烷基的引入顺序至关重要。某些酯不能反应的解释是由于不能进行烯醇化。