Cinchona steric properties

Excellent results were also reported recently by Maruoka and coworkers by using 50% aqueous NaOH in toluene and a (5)-BINAP-derived C2-symmetric ammonium catalyst 14 [64]. The steric and/or electronic properties of this new class of catalysts can be finely tuned in order to improve reactivity and enantioselectivity. The N-spiro structure along with their high lipophilicity make such catalysts much more reactive than the traditional PTC catalysts, e.g., Bu4N+Br, in otherwise identical conditions [65]. Excellent ees are usually obtained in short reaction times with 1 % of catalyst only moreover, they should be more stable under basic conditions than ammonium salt derived from Cinchona alkaloids since they do not undergo Hofmann elimination resulting from lack of yS-hydrogens. However, they are not as easily prepared as Cinchona ammonium catalysts and are expected to be quite expensive since they are not derived from the chiral pool. On... 

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