Syntheses and optical rotatory dispersion studies of S-5-(2-pentyl)barbituric acid derivatives

Palladium-Catalyzed Asymmetric Allylic Alkylation of Barbituric Acid Derivatives: Enantioselective Syntheses of Cyclopentobarbital and Pentobarbital

“…Pentobarbital (5-ethyl-5-(1-methyl-1-butyl)barbituric acid, 9 ) is also a sedative/hypnotic. The ( R )-enantiomer has been synthesized from a chiral starting material, ( R )-pulegone; however, the ( S )-enantiomer has proven much more difficult to make in high optical purity . We began our studies by applying the reaction conditions developed for cyclopentobarbital to the reaction of barbiturate 6 with allylic carbonate 7 using ligand L1 to give barbituric acid derivative 8 (eq 4).…”

“…Pentobarbital (5-Ethyl-5-(1-methylbutyl)barbituric Acid, 9). , Barbiturate 8 (110 mg, 0.49 mmol), 10% palladium on charcoal (52 mg, 0.049 mmol), and methanol (5 mL) were placed in a 15 mL round-bottom flask. The flask was flushed with hydrogen and then stirred under hydrogen for 1 h. The mixture was filtered through silica gel with ether and then concentrated in vacuo .…”

“…The absolute configuration was determined by comparison of the rotation to that reported in the literature (ref ). Thus, using the ( R ,R )-L1, ( R )- 9 was obtained.…”

Circular dichroism and carbon-13 nuclear magnetic resonance spectra of (S)-5-alkyl-5-(2'-pentyl)-2-thiobarbituric acids

“…5 The title compounds were prepared by a procedure previously reported for similar 5-alkyl-5-(2'-pentyl)-2-thiobarbituric acids. 10 The following new compounds were prepared. 5-Methyl-5-(2'pentyl)-2-thiobarbituric acid (2, R = CHs) was recrystallized from EtOAc-hexane and had mp 85-86°.…”