Base-promoted diastereoselective α-alkylation of borane <i>N</i>-((<i>S</i>)-1′-phenylethyl)azetidine-2-carboxylic acid ester complexes
作者:Eiji Tayama、Ryotaro Nishio、Yoshiaki Kobayashi
DOI:10.1039/c8ob01395k
日期:——
base-promoted α-alkylation of N-((S)-1-phenylethyl)azetidine-2-carboxylic acid esters 1 was investigated. The use of diastereomerically pure borane complexes 3 as substrates, which are easily prepared from 1, dramatically improved the yields and diastereoselectivities of α-alkylated products 2. For example, the treatment of tert-butyl ester (1S,2S,1′S)-3a with 2.4 equivalents of lithium bis(trimethysilyl)amide
研究了N -((S)-1-苯乙基)氮杂环丁烷-2-羧酸酯1的碱促进的α-烷基化。使用非对映体纯的硼烷络合物3作为底物,可以很容易地由1制备,大大提高了α-烷基化产物2的收率和非对映选择性。例如,叔丁基酯(1 S,2 S,1 'S)-3a在0°C下用2.4当量的双(三甲基甲硅烷基)酰胺锂(LiHMDS)处理,然后在2.6当量的苄基溴中处理,得到α-苄基化(2 S,1 'S)-2aa,几乎只有一种非对映异构体,收率为90%。我们的方法能够从市售的(S)-1-苯基乙胺开始生产旋光性α-取代的氮杂环丁烷-2-羧酸酯,这是最便宜的手性化合物之一。