Chiral Lewis Acid Controlled Synthesis (CLAC Synthesis): Chiral Lewis Acids Influence the Reaction Course in Asymmetric Aldol Reactions for the Synthesis of Enantiomeric Dihydroxythioester Derivatives in the Presence of Chiral Diamines Derived from L‐Proline
1997; Wiley; Volume: 3; Issue: 9 Linguagem: Inglês
10.1002/chem.19970030914
ISSN1521-3765
Autores Tópico(s)Chemical Synthesis and Reactions
ResumoAbstract Both enantiomers of 2,3‐dihy‐droxythioester derivatives were prepared with almost perfect stereochemical control by chiral Lewis acid controlled synthesis (CLAC synthesis). CLAC synthesis means synthesis of all individual diastereomers or enantiomers from the same starting materials by designing chiral Lewis acids. For example, (Z)‐1‐ethyl‐thio‐1‐(trimethylsiloxy)‐2‐( tert ‐butyldi‐methylsiloxy)ethene ( 1 ) reacted with aldehydes in the presence of chiral tin(II) Lewis acids using ( S )‐1‐methyl‐2‐[(isoin‐dolinyl)methyl]pyrrolidine ( 4 ) and ( S )‐1‐methyl‐2‐[(indolinyl)methyl]pyrrolidine ( 5 ) to afford enantiomeric dihydroxy‐thioester derivatives. Chiral diamines 4 and 5 , which were readily prepared from L‐proline, differ only in the fusion point of the benzene ring connected to the pyrrolidine moiety. The unique selectivities were ascribed to the conformational difference between the chiral tin(II) Lewis acids of chiral diamines 4 and 5 , and the function of chiral sources for obtaining high selectivities has also been clarified.
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