SYNTHESIS AND STEREOCHEMICAL BEHAVIOR OF 8-ALKYL-3-(1-PHENYLETHYL)-7-OXA-1,3-DIAZABICYCLO-[3.2.1]-OCTANE-4,6-DIONES DIRECTED TOWARDS THE SYNTHESIS OF ALPHA-SUBSTITUTED BETA-AMINO ACIDS

A diastereoselective synthesis of enantiomerically pure a-hydroxymethyl p-amino acid derivatives is described starting from a,P-unsaturated acids. The unsaturated adds are transformed through simple steps into chiral perhydropyrimidin-4-ones that are diastereoselectively transformed into [3.2.1]-1,3-diaza-7-oxabicyclooctan-4,6-diones by reaction with LiHMDS. The bicycle 9b is opened by reaction with methanol under acid catalysis and the product 10 is selectively reduced to afford the desired compound.