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Intramolecular Acceleration of Asymmetric Epoxide Ring‐Opening by Dendritic Polyglycerol Salen–Cr III Complexes
Author(s) -
Keilitz Juliane,
Haag Rainer
Publication year - 2009
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200900241
Subject(s) - chemistry , epoxide , catalysis , intramolecular force , ring (chemistry) , polymer chemistry , cyclopentene , pyrrolidine , cyclohexene oxide , bimetallic strip , cyclohexene , medicinal chemistry , enantioselective synthesis , stereochemistry , organic chemistry
We present the synthesis of symmetrical (pyrrolidine‐salen)Cr III complexes immobilized on hyperbranched polyglycerol 1 through linkers of different lengths and their application in the asymmetric ring‐opening of meso ‐epoxides. This reaction proceeded through a cooperative bimetallic mechanism and for the polymeric catalysts a positive dendritic effect with regard to the reaction rate was found. In addition, the introduction of long linkers (C6, C10, and C18) forced the favored head‐to‐tail orientation of two catalyst molecules and led to greater enantioselectivity with ee values of 48 % (cyclohexene oxide) and 64 % (cyclopentene oxide) for the ring‐opening of meso ‐epoxides with TMSN 3 catalyzed by hPG‐C10‐CrCl ( 13 ). The soluble polyglycerol‐supported catalyst was recovered five times by dialysis to afford similar activities and a 10 % increase in the enantioselectivity.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)