Substituted Isoquinolines by Noyori Transfer Hydrogenation: Enantioselective Synthesis of Chiral Diamines Containing an Aniline Subunit.
Transfer hydrogenation using the Noyori catalyst 5-Ts is effective for the enantioselective hydrogenation of imines containing fully substituted nitrogen groups (12 or 13). Analogues such as 11c could not be reduced in practical yield, apparently due to product inhibition of the catalyst. Asymmetric transfer hydrogenation of the aniline imine 8a was possible, but required impractical purity levels for the substrate, and the nitro analogue 7 could not be reduced efficiently. The best results were obtained with the bromophenyl imine 20. In the case of 20b, the product 21b was formed with 98.7% ee, and the material could be upgraded to >99% ee by crystallization of the hydrochloride salt. Reaction of 21b with NH(3) or MeNH(2) in the presence of Cu/CuCl gave the chiral anilines 10b or 23b. The latter substance is comparable to the commercially available 1 as a chiral proton donor for amide enolates and provides access to the hitherto unavailable enantiomeric series.
Vedejs
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Organic Synthesis Institute, Riga, Latvia LV 1006.
Trapencieris
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Suna
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