Neighbouring group effects promote substitution reactions over elimination and provide a stereocontrolled route to chloramphenicol
作者:Christopher J. Easton、Craig A. Hutton、Martin C. Merrett、Edward R.T. Tiekink
DOI:10.1016/0040-4020(96)00307-9
日期:1996.5
In reactions of β-brominated valine and p-nitrophenylalanine derivatives to give β-hydroxy amino acid derivatives the carboxyl group, when protected as an amide, exerts a neighbouring group effect to facilitate the substitution process, and reduce competing elimination reactions. As a consequence of the effect, the (2R,3R)- and (2R,3S)-stereoisomers of 3-bromo-N-tert-butyl-Nα-phthaloyl-p-nitrophenylalaninamide
在β-溴化缬氨酸和对硝基苯丙氨酸衍生物反应生成β-羟基氨基酸衍生物的反应中,羧基作为酰胺被保护时,发挥邻近基团作用,以促进取代过程,并减少竞争性消除反应。作为效果的结果,(2 - [R,3 - [R )-和(2 - [R,3小号)的3-溴-立体异构体ñ -叔丁基- ñ α -phthaloyl- p -nitrophenylalaninamide两者反应,得到( 2小号,3 - [R)-3-羟基ñ -叔丁基- ñ α-邻苯二甲酰基-对-硝基苯丙氨酰胺,提供立体收敛的氯霉素途径。