The reaction of lithiating agents with various 3-bromopyridines has been investigated. An unprecedented selectivity was observed with t-BuLi, which effected a clean lithiation at C-4. With 3-bromo and 2-chloro-3-bromo pyridines, the ortholithiation-exchange ratio was strongly electrophile and addition order dependent while 2-chloro-5-bromopyridine always gave exclusive C-4 substitution.
对各种3-
溴吡啶与
锂化试剂的反应进行了研究。使用t-BuLi时观察到了前所未有的选择性,在C-4位置实现了干净的
锂化。对于3-
溴和2-
氯-3-
溴吡啶,邻位
锂化的交换比在很大程度上依赖于电亲和性和加成顺序,而2-
氯-5-
溴吡啶则始终只产生C-4取代反应。