Synthesis of new BPPFA analogues, having exchanged one of the N-methyl groups for a long (–C10H20–) or short (–C4H8–) alkyl chain with a terminal methoxycarbonyl group, and their immobilization on silica are described. Immobilization resulted in considerable lowering of the reaction rates as well as stereoselectivity in hydrogenation
reactions. On the other hand, both homogeneous 3a as well as immobilized ligand 6a
with a longer spacer (–C10H20–) have activities and enantioselectivities in allylic nucleophilic substitution comparable to the known BPPFA ligand. This is true also for homogeneous ligand 3b with a shorter chain (–C4H8–), but its immobilization resulted in a big drop of activity as well as selectivity.
本研究介绍了一种新的
BPPFA 类似物的合成及其在
二氧化硅上的固定化情况,该类似物将一个 N-甲基基团交换为带有末端甲氧基羰基的长(-
C10H20-)或短(-
C4H8-)烷基链。固定化技术大大降低了氢化反应的反应速率和立体选择性。另一方面,均质
配体 3a 和固定化
配体 6a 在烯丙基亲核取代反应中的活性和对映体选择性与已知的
BPPFA
配体相当。具有较短链(- -)的均质
配体 3b 也是如此,但其固定化导致活性和选择性大幅下降。