The asymmetric Diels-Alder cycloaddition of cyclopentadiene (II) with the acrylic ester (I) of the chiral auxiliary D-pantolactone catalyzed by TiCl4 gives the chiral norbornene (III), which is treated with LiOH or NaOH to eliminate the auxiliary to yield the carboxylic acid (IV). The reaction of (IV) with oxalyl chloride affords the acyl chloride (V), which is condensed with 5,6-diamino-1,3-dipropyluracil (VI) by means of DMAP in pyridine to provide the amide (VII). The cyclization of (VII) by means of NaOH in dioxane gives the 1,3-dipropylxanthine derivative (VIII), which is finally epoxidated by means of magnesium monoperphthalate (MMPP) in aq. isopropanol to furnish the target xanthine derivative.

The asymmetric Diels-Alder cycloaddition of cyclopentadiene (II) with the acrylic ester (I) of the chiral auxiliary D-pantolactone catalyzed by TiCl4 gives the chiral norbornene (III), which is treated with LiOH or NaOH to eliminate the auxiliary to yield the carboxylic acid (IV). The reaction of (IV) with oxalyl chloride affords the acyl chloride (V), which is condensed with 5,6-diamino-1,3-dipropyluracil (VI) by means of DMAP in pyridine to provide the amide (VII). The cyclization of (VII) by means of NaOH in dioxane gives the 1,3-dipropylxanthine derivative (VIII), which is finally epoxidated by means of magnesium monoperphthalate (MMPP) in aq. isopropanol to furnish the target xanthine derivative.