engleski

A Highly Stereocontrolled Synthesis of S-(-)-1-(4-tert-Butyl)phenyl-2-methyl-3-N-(cis-3, 5-dimethyl)morpholinylpropane via Chiral Mannich Reaction

By employing cis-2, 6-dimethylmorpholinemethylene immonium tetrachloroaluminate (5) enamines 9 and 10, prepared from 4-tert-butylpropiophenone and propiophenone with (R)-(-)-2-(methoxymethyl)pyrrolidine (8), were converted to chiral Mannich bases 11, 12 with nearly 100% ee ; optical purity of these β -amino ketones drops significantly during isolation. Two-step reduction of the keto group in 11, 12 afforded (S)-(-)-3-(4-tert-Butyl)phenyl-1-N-(cis-2, 6-dimethyl)morpholinyl-2-methylpropane (1), (S)-enantiomer of racemic systemic fungicide, generic name fenpropimorph, and its congener 13 with 95.1% and 90.7% ee, respectively. A mechanistic model for asymmetric induction in the diastereoselective step is proposed.

Chemoenzymatic synthesis. Substituted morpholines. Stereochemical aspects. Carbonyl-compounds. Enamine synthesis

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