不对称α-烃基-α-羟基丙二酰胺衍生物的合成新方法

Novel Method for Synthesis of Unsymmetrical α-Organyl-α-hydroxymalonamide Derivatives

N,N-二甲基氨甲酰基三甲基硅烷与一系列N-甲基-N-甲氧甲基α-羰基酰胺在无水无氧、105℃的条件下反应,合成了不对称α-烃基-α-羟基丙二酰胺类化合物或不对称α-烃基-α-三甲基硅氧基丙二酰胺衍生物,收率71%～86%,其结构用元素分析、1H NMR、13C NMR和IR等方法进行了表征.通过研究反应的影响因素发现,反应底物α-羰基酰胺中与α-羰基直接相连的烃基的空间位阻是该加成反应的重要影响因素,而α-羰基直接相连的芳环上取代基的电子效应则主要影响反应完成的时间.并提出了可能的反应机理.

Aldehydes may be directly converted to O-silyl-a-hydroxyamides by reaction with N-methoxymethyl-N-methyl- carbamoyl（trimethyl）silane. In an attempt to extend this chemistry, we found that N-methoxymethyl-N-methylcar- bamoyl（trimethyl）silane did not react with a-ketoamides. So we started testing activity within the variety of carbonyl com- pounds towards N^V-dimethylcarbamoylsilane and found that the addition reaction of N,N-dimethylcarbamoyl（trimethyl）- silane with a series of N-methyl-N-methoxymethyl-a-ketoamides could afford good yields （71%-86%） of unsymmetrical a-organyl-a-hydroxymalonamide derivatives or unsymmetrical a-organyl-a-siloxymalonamide compounds. When 1.2 equiv. of a carbamoylsilane 1 was allowed to react with a-ketoamides 2 in anhydrous toluene solution under anhydrous conditions at ambient conditions or below, good yields of a-siloxyamides 3 were obtained, generally within long time. Their structures were characterized by elemental analysis, IH NMR, 13C NMR and IR spectra. A novel method for synthesis of unsymmetrical a-organyl-a-hydroxymalonamide derivatives was provided. The experiments indicated that the steric environment was an important factor in the addition reaction since longer reaction time was needed both in case of 2b and 2e than in case of 2a, and the electronic effect influenced on the rate of the reaction since the yields were obtained about the same from a variety of aryl-a-ketoamides, the stronger donor ability of substituted group on the benzene ring of the aryl-a-ketoamides, the longer reaction time was needed. A reaction mechanism involving two intermediates is proposed, in which carbamoylsilane 1 can rearrange to its nucleophilic carbene form A, which attacked the carbonyl group of a-ketoamides to produce an unstable intermediate B, the subsequent silyl group transfer leads to corresponding the O-silylated adducts 3. The latter can be hydrolyzed to form the a-organyl-a-hydroxymalonamide derivatives 4.