The alkylation of benzyl N-Boc pyroglutamate was carried out using chloroformates in order to introduce an activating group at the 4-position. Deprotonation with three equivalents of LiHMDS followed by alkylation with different electrophiles lead to 2-alkylated pyroglutamates. The directing effect of the alkylation to the 2-position can be accounted for by the formation of a counterion complex.
N-Boc焦谷
氨酸苄酯的烷基化反应使用
氯甲酸酯进行,以便在4位引入一个活化基团。用三当量的Li
HMDS脱质子化,然后用不同的亲电试剂进行烷基化,得到2-烷基化的焦谷
氨酸。烷基化对2位的定向作用可以通过形成反离子络合物来解释。