SYNTHESIS AND REACTIONS OF BIGINELLI COMPOUNDS .5. FACILE PREPARATION AND RESOLUTION OF A STABLE 5-DIHYDROPYRIMIDINECARBOXYLIC ACID

The synthesis of enantiomerically pure 5-dihydropyrimidinecarboxylic acids 7a,b is described. Condensation of benzyl acetoacetate with methylurea and 2-naphthaldehyde gave Biginelli compound 3b, which after methylation and removal of the benzyl group led to racemic acid 5b. Fractional crystallization of diastereomeric alpha-methylbenzylammonium salts 6a,b followed by acidification provided the desired optically pure carboxylic acids 7a,b. Conversion of 7a,b to carboxylic acid azides 8a,b, followed by Curtius rearrangement and reaction with 10-undecenol led to chiral urethanes 10a,b. The absolute stereochemistry of acids 7a,b was established by X-ray analysis of diastereomeric alpha-methylbenzylammonium-carboxylate 6c.