method for the preparation of enantiomerically pure inherentlychiralcalix[4]arene phosphonic acid (cR,pR)-7 in four steps starting from the readily available and previously synthesized (cS)-enantiomer of calix[4]arene acetic acid 1 or its methyl ester 2 was developed. The first tests of this unique calixarene Brönsted acid with inherent chirality in organocatalysis of the aza-Diels–Alder reaction
In the presence of 1-5 mol % of a chiral zirconium catalyst, aza Diels-Alder reactions of aldimines with Danisheisky's dienes proceeded smoothly to afford the corresponding piperidine derivatives in high yields with high enantioselectivities. For the catalyst optimization, solid-phase and liquid-phase methods were successfully used. In the solid-phase approach, polymer-supported (R)-1,1'-binaphthols (BINOLs) have been synthesized and rapid optimization using the solid-phase reactions has been achieved. On the other hand, novel chiral zirconium cyanides were developed as excellent catalysts using the liquid-phase approach.
作者:Václav Jurčík、Kenzo Arai、Matthew M. Salter、Yasuhiro Yamashita、Shū Kobayashi
DOI:10.1002/adsc.200700615
日期:2008.3.25
Niobium-based chiral Lewis acid was found to be highly effective catalyst for aza-Diels–Alderreactions of imines with Danishefsky‘s dienes. The reactions proceed in high yield with high enantioselectivity for both aromatic and aliphatic imines. The developed methodology was applied to total synthesis of (+)-anabasine.