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Synthesis of Novel Tridentate N,O,S and N,N,O Ligands of the Tripod Type in Racemic and Enantiomerically Pure Form
Author(s) -
Berkessel Albrecht,
Frauenkron Matthias,
Nowak Thorsten,
Schwenkreis Thomas,
Seidel Lutz,
Steinmetz Adrian,
Bolte Michael
Publication year - 1996
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19961290113
Subject(s) - chemistry , thioether , substituent , imidazole , stereochemistry , absolute configuration , tripod (photography) , enantiomer , amine gas treating , reductive amination , medicinal chemistry , enantioselective synthesis , organic chemistry , catalysis , physics , optics
A series of seven chiral, tripodal N,O,S and N,N,O ligands were prepared in which N stands for a secondary amine or imidazole donor, O for a phenol, and S for a thioether or thiol metal‐binding group. Key steps are (1) the construction of ortho ‐hydroxyacetophenones bearing the phenolic binding group and either a thioether, a protected thiol or an imidazole substituent in the α‐position, and (2) subsequent reductive amination with a primary amine. The modular synthesis allows a rapid construction of a variety of structurally related ligands. In three cases, the enantiomers of the racemic products could be separated after condensation with ( R )‐glyceraldehyde acetonide as chiral auxiliary. The relative configurations of the cyclic N,O‐ and N,N‐acetals thus obtained were established by NOE spectroscopy. X‐ray structural analysis of two crystalline N,O‐ and N,N‐acetals allowed the assignment of absolute configurations. Hydrolysis of the dia‐stereomerically pure acetals afforded the enantiomerically pure ligands in high yield. By comparison of their CD spectra, absolute configuration could also be assigned to the third pair of enantiomerically pure ligands.