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Matrix synthesis of chiral carboxy derivatives: Aldehyde chiral discrimination due to a two‐point coordination of Mg 2+
Author(s) -
Beluzhenko Olga V.,
Bogdanova Galina V.,
Tumenev Vitalii A.,
Zhdanov Yurii A.
Publication year - 1993
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.530050611
Subject(s) - chemistry , diastereomer , steric effects , stereochemistry , stereoselectivity , molecule , aryl , asymmetric carbon , aldehyde , matrix (chemical analysis) , asymmetric induction , computational chemistry , enantioselective synthesis , organic chemistry , catalysis , optically active , alkyl , chromatography
To control stereoselectivity in aldol‐like reactions with chiral carbohydrate templates, we studied the interaction between completely protected dialdo compounds and magnesium enediolates of arylacetic acids. Diastereomeric mixtures of the highly functionalized acids obtained were esterified to isolate individual methyl uronates. It was found that all the diastereomeric esters exhibit Cotton effects of the same positive sign in the 220–230 nm region and so possess the same S configuration of the aryl chiral center C(6). Chiral center C(5) configurational assignments were performed using IR and ORD spectroscopy. We separated and specified four pairs of diastereomeric methyl uronates. It follows that the precursory acids have the same 5R*, 6S (major isomers) and 5S*, 6S (minor isomers) configurations. A tentative mechanism for complexation and possible models of Mg 2+ ‐protected dialdose intermediate complexes has been proposed. We have concluded that a kind of orbital steering is realized, accompanied by some “tuning” of molecular assembly conditioned by two‐point coordination between Mg 2+ and potential cation‐binding sites in the substrate molecules. Thus it has been demonstrated that reasonable diastereo‐selectivity can be achieved even through the use of small matrix molecules using rather small functional groups, which do not impose any stringent steric requirements. © 1993 Wiley‐Liss, Inc.