Chiral electrophilic ''glycinal'' equivalents. New synthons for optically active alpha-amino acids and 4-substituted 2-oxazolidinones

The thermal reaction of 3-[(IS)-2-alkoxy-1-apocamphanecarbonyl]-2-oxazolones (21a-c) with dialkyl azodicarboxylates (9) results in exclusive formation of [4 + 2] type cycloadducts (22 and 23) with moderate levels of diastereofacial selection (up to 72% d.e.). The diastereomers thus obtained were readily purified and subsequent treatment with acidic methanol followed by removal of the auxiliary with LiBH4/MeOH (1:2) gave optically pure 4-methoxy-5-hydrazino-2-oxazolidinones (26 and 27), which serve as alpha-aminoaldehyde templates useful for the synthesis of a wide variety of optically active alpha-amino acids as well as 4-alkyl and 4-aryl-2-oxazolidinones. (C) 1997, Elsevier Science Ltd.