Enantioselective addition of oxazolones to maleimides. An easy entry to quaternary aminoacids

The catalytic enantioselective addition of 2-tert-butyl-4-aryl-1,3-oxazol- 5-ones to maleimides is reported. The addition takes place exclusively at the C-4 position of the oxazolone ring, giving access to quaternary amino acid derivatives. The reaction is catalyzed by readily available chiral bases such as (DHQD)₂PYR, rendering the final compounds in good yields and with moderate to good diastereo- and enantioselectivities. When the C-4-substituent of the 2-tert-butyl-oxazolone is an alkyl group, the regioisomeric C-2 addition product is also obtained.