Phenyl- and 2,7-Naphthyl-Linked Dimeric Cinchona-PTCs

3-Phenyl- and 2,7-Naphthyl-Linked Dimeric Cinchona-PTCs 

In the Park-Jew group s systematic investigation, two types of catalyst - the 1,3-phenyl- and 2,7-naphthyl-based dimeric ammonium salts - were selected as an efficient skeleton of chiral PTCs for the catalytic asymmetric phase-transfer alkylation 

a very high enantioselectivity (98% ee) as well as ahigh chemical yield (95%) was obtained within a short reaction time (30 min). Notably, all of the PTCs were able to conserve their high catalytic efficiency in terms of both reactivity and enantioselectivity, even when present in smaller quantities (1 mol%). 

Interestingly, the molecular structure of the 2,7-naphthyl catalysts 39 and 40 markedly resembles that of the 1,3-phenyl catalysts 37 and 38, respectively the only difference is the distance between the two cinchona alkaloid units. The naphthalene linker is about 2.4 A longer than the benzene linker. The Park-Jew group proposed that the reason for the higher enantioselectivity of the 2,7-naphthyl catalyst was that the 2,7-naphthalene linker might confer a spatial benefit to form a more favorable conformation by decreasing the steric hindrance between the two cinchona units compared to that in the 1,3-benzene linker. 

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