Catalytic Asymmetric Intramolecular Aminopalladation:  Enantioselective Synthesis of Vinyl-Substituted 2-Oxazolidinones, 2-Imidazolidinones, and 2-Pyrrolidinones

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.