Stereoselective inter- and intramolecular Pauson-Khand reactions of N- (2-alkynoyl) derivatives of chiral oxazolidin-2-ones

A complete account of the intermolecular and intramolecular Pauson-Khand reactions of N-(2-alkynoyl) derivatives of chiral 2-oxazolidinones is presented. The intermolecular Pauson-Khand reactions with norbornene or norbornadiene take place under mild conditions and in high yields. Phenyl-or trimethylsilylpropiolate derivatives lead to the exclusive formation of 1,4- dicarbonyl regioisomers, while mixtures of 1,3- and 1,4-regioisomers are obtained with tetrolate derivatives. The diastereoselectivity of the reaction, determined by the substitution pattern of the oxazolidinone moieties, can be very high (up to 17.5:1 dr) for the formation of 1,4- dicarbonyl regioisomers, and the diastereomeric products can often be separated by column chromatography. Under the appropriate conditions, the intramolecular Pauson-Khand reactions of oxazolidinone-derived enynes can also take place with very good yields, but with low diastereoselectivities. The absolute configurations of several adducts have been determined, and the stereochemical outcome of the reaction has been rationalized.