Chiral binaphthyl- and biphenyl-modified

Binaphthyl- and Biphenyl-Modified Chiral Phase-Transfer Catalysts for Asymmetric Synthesis... 

S)-40 Ar = 3,4,5-F3C0H2 Figure 12.9 Chiral binaphthyl- and biphenyl-modified quaternary ammonium salt phase-transfer catalysts... 

This unique phenomenon provides a powerful strategy in the molecular design of chiral catalysts that is, the requisite chirality can be served by the simple binaphthyl moiety, while an additional structural requirement for fine-tuning of reactivity and selectivity can be fulfilled by an easily modifiable achiral biphenyl structure. This certainly obviates the use of two chiral units, and should be appreciated in the synthesis of a variety of chiral catalysts with different steric and/or electronic properties. Actually, quaternary ammonium bromide possessing a sterically demanding substituent such as (S)-12b can be easily prepared, and benzylation with (S)-12b as catalyst gave 9 in 95% yield with 92% ee. Further, theenantioselectivity was enhanced to 95% ee with (S)-12c as a catalyst [12]. 

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