Polymeric Cinchona-PTCs with Other Linkers

Polymeric Cinchona-PTCs with Other Linkers 

In the cases of catalysts containing the naphthalene linker (30-35), the 1,4-, 1,5-, and 2,7-substituted catalysts 30, 31 and 35 gave good enantioselectivities [13], Whereas, the 2,6-substituted catalyst 34 yielded a moderate result, the sterically hindered catalysts 32 and 33 showed poor enantioselectivities. Especially, the 2,7-naphthalene-linked catalyst 35 was found to possess excellent catalytic activity for this alkylation from the viewpoints of enantioselectivity and chemical yield. 

Based on the fact that the meta-relationship in catalyst 7 showed good activity in asymmetric alkylation, the same concept was applied to the 1,3,5-trimeric catalyst 36, in which all cinchona units on the phenyl ring were placed in the meta-position to each other hence, it would be expected this relationship might increase or maintain the catalytic efficiency of the meta-dimeric effect. Compared with the result from 7, the effect of trimerization could be regarded as quite similar to that of the metadirecting-dimerization in chemical and optical yields [14]. 

---

Polymeric Cinchona-PTCs with Other Linkers... 

Figure 4.8 Polymeric cinchona-PTCs with other linkers.

---