Catalytic asymmetric intramolecular aminopalladation: enantioselective synthesis of vinyl-substituted 2-oxazolidinones, 2-imidazolidinones, and 2-pyrrolidinones. |
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Authors: | Larry E Overman Travis P Remarchuk |
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Institution: | Department of Chemistry, 516 Rowland Hall, University of California Irvine, California 92697-2025, USA. |
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Abstract: | A new catalytic asymmetric synthesis of five-membered nitrogen heterocycles is reported. This synthesis employs ferrocenyloxazoline palladacycles (FOP trifluoroacetate catalysts) 2 and 4 and proceeds by a catalytic cycle involving Pd(II) intermediates. For example, prochiral (Z)-4-acetoxy-2-buten-1-ols are condensed with an arylsulfonyl isocyanate and the derived allylic N-arylsulfonylcarbamates cyclize in situ upon addition of 0.5-5 mol % of 2 or 4 to form 4-vinyloxazolidin-2-ones 6, 13, and 15 in high yield and 89-99% ee. The related 2-pyrrolidinone 19 and 2-imidazolidinone 18 are prepared in similar fashion. Pyrrolidinone 19 can be converted in two steps to the unnatural enantiomer of the GABA inhibitor vigabatrin 20. |
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