Enantiomerically pure tetrahydropyrimidinones in asymmetric synthesis: Preparation of a protected alpha-methylasparagine derivative and correspondingdipeptides

Methyl eater 5a, available in enantiomerically pure form from the amino aci d asparagine via a one-pot cyclization/protection sequence, followed by est erification, can be effectively deprotonated with LDA/DMPU/LiCl. Treatment with Mel affords the corresponding alkylated adduct in enantiomerically pur e form, from which alpha-methylaspartic acid is obtained. Variation of the amine protection group allows for the isolation of a protected carboxylic a cid/free amine derivative of alpha-methylasparagine. The utility of H-MeAsn -OMe is demonstrated in the formation of dipeptides.