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A Novel Counterion Effect on the Diastereoselectivity in the Mn III (salen)‐Catalyzed Epoxidation of Phenyl‐Substituted cis ‐Alkenes
Author(s) -
Adam Waldemar,
Roschmann Konrad J.,
SahaMöller Chantu R.
Publication year - 2000
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 - 10.1002/1099-0690(200011)2000:21<3519::aid-ejoc3519>3.0.co;2-f
Subject(s) - counterion , chemistry , isomerization , catalysis , reactivity (psychology) , medicinal chemistry , benzene , ligand (biochemistry) , stereochemistry , photochemistry , ion , organic chemistry , pathology , medicine , biochemistry , alternative medicine , receptor
The catalytic oxidation of the phenyl‐substituted cis alkenes 1a,b by the Mn III (salen)X complexes 3a−f with iodosyl benzene (PhIO) as oxygen source affords the corresponding epoxides 2a,b in cis / trans ratios of 79:21 to 26:74. The diastereoselectivity ( cis / trans ratio) depends on the counterion of the Mn III (salen)X complexes 3a−f . Thus, for the complexes 3a−c (Cl − , Br − and AcO − as ligating counterions) extensive isomerization ( cis / trans ratio ca. 30:70) takes place, while for the complexes 3d−f (BF 4 − , PF 6 − and SbF 6 − as nonligating counterions) only moderate isomerization ( cis / trans ratio ca. 75:25) is observed. This counterion effect may be rationalized in terms of the two‐state reactivity paradigm; specifically, the axial ligand in the radical intermediate alters the triplet‐quintet energy gap.