3-dioxolane-4,5-dimethanolato(2−)-O,O′]titanium ((R)-1b) are efficient catalysts for the electrophilic enantioselective chlorination and bromination of β-keto esters with N-chlorosuccinimide (NCS) and N-bromosuccinimide (NBS), respectively. With 5 mol-% of catalyst at room temperature an enantioselectivity of up to 88% ee could be obtained for the chlorination reaction. Under comparable conditions, bromination
Ti(TADDOLato) 络合物二
氯[(4R,5R)-2,2-二甲基-α,α,α',α'-四苯基-
1,3-二氧戊环-4,5-二
甲醇合(2-)-O, O']
钛((R)-1a)和二
氯[(4R,5R)-2,2-二甲基-α,α,α',α'-四(
萘-1-基)-
1,3-二氧戊环-4,5-二
甲醇(2-)-O,O']
钛((R)-1b)是β-
酮酯与N-
氯代琥珀
酰亚胺(
NCS)和N-
溴代琥珀
酰亚胺的亲电子对映选择性
氯化和
溴化的有效催化剂(国家统计局),分别。在室温下使用 5 mol-% 的催化剂,
氯化反应可以获得高达 88% ee 的对映选择性。在可比较的条件下,
溴化反应较慢且立体选择性较低。