Diastereoselective α-alkoxylation of lactamide N-alkyl groups via intramolecular formation of oxonium ions as the key intermediate
作者:Tohru Kamada、Akira Oku
DOI:10.1039/a805638b
日期:——
Stereoselective introduction of an alkoxy group to the amine unit of lactamide derivatives, under electrochemical oxidation conditions, was investigated based upon the assumption that a cyclic oxonium ion can be formed between the alkoxy substituent on the chiral center and a carbocation generated at the α-position of N-alkyl substituents. With N-monosubstituted lactamides, diastereoselectivity in the N-α-alkoxylated product was not observed. With N,N-disubstituted lactamides, however, the selectivity appeared though in low ratios (â2.2). Requisite factors that govern the stereoselectivity, i.e. nucleophilicity of both internal and external nucleophiles and substitution on amine units, were also examined.
在研究电化学氧化条件下,氨基酸酰胺衍生物的醇氧基团的立体选择性引入时,假设在手性中心的醇氧基取代基与在N-烷基取代基的α位生成的碳正离子之间可以形成循环氧鎓离子。对于N-单取代的酰胺类化合物,在N-α-醇氧基化产物中没有观察到二芴选择性。然而,对于N,N-二取代的酰胺类化合物,尽管选择性很低(≈2.2),但还是出现了选择性。还研究了影响立体选择性的必要因素,即内部和外部亲核试剂的亲核性以及氨基单元的取代情况。