Heterocycles. XXV. Sodium Borohydride Reduction of Flavanonols
Solvent effects on the stereochemistry in the sodium borohydride reduction of (+/-)-flavanonols have been examined.The effects observed for the (+/-)-flavanonols with 5-OMe in 2-propanol, dioxane and methanol are explainable by the differences between the steric interactions inherent in the product-like transition states A and B.It has been also found that 5-OAc peculiarly affects the stereochemistry in the reduction to produce the (+/-)-catechin-type compounds in a one-pot process.The solvent and temperature effects are examined using a model analogous to the above.
Heterocycles. XXII. Stereoselective Synthesis of (+)-Aromadendrin Trimethyl Ether and Its Enantiomer, and Their Reduction
Two enantiomeric chalcone epoxides 2a and 2b are synthesized under phase-transfer conditions using 1-benzylquinidinium chloride and 1-benzylquininium chloride as catalysts, respectively.Stereoselective cyclisation of 2a and 2b, followed by methylation and
HETEROCYCLES. XVIII. SYNTHESIS OF THE RACEMATES OF NATURALLY OCCURRING FLAVONOIDS
Racemic aromadendrin and fustin have been stereoselectively synthesized.Reduction of the O-substituted derivatives of these flavanonols provides the corresponding derivatives of gleditsin, leucopelargonidin and mollisacacidin (leucofisetinidin).