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Stereoselective cyclopropanation and ring-opening: application to the synthesis of pure (S)-2-methyl-3-arylpropylamines

Stereoselective catalytic and stoichiometric cyclopropanation of styrenes 3a, 3b was studied ; stoichiometric method turned out superior in the terms of enantioselectivity. The intermediary carboxymethyl cyclopropane 11a, 11b, obtained on reduction of carbethoxy derivatives 4a, 4b, were hydrogenolyzed to (S)-1, 3-substituted-2-methylpropanes 15a, 15b. The highest conversion and regioselectivity was obtained with 3% Pd/C as the catalyst. The final steps, chlorination of alcohol 15a into 19a, and alkylation of cyclic sec amines were already demonstrated by us (ref. 2c) to afford (S)-(-)-2-(4-tert-butylphenyl)-1-cis-2, 6-dimethylmorpholyl)propane (S-1a) and (S)-(-)-2-(4-tert-butylphenyl)-1-piperidylpropane (S-2a), the (S)-enantiomers of two systemic fungicides presently commercialized as racemates, without any lost of enantiomeric purity.

Optically-active siloxycyclopropanes ; Chemoenzymatic synthesis ; Asymmetric catalysis ; Substituted cyclopropanes ; Hydrogenolysis ; Regioselectivity ; Ligands

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