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 cyclization of 2a and 2b, followed by methylation and preparative high performance liquid chromatography gives pure (+)-aromadendrin trimethyl ether (4a) and its enantiomer 4b. Reduction of pure 4a and 4b with NaBH4. affords four pure flavan-3, 4-diol trimethyl ethers, 5a, 6a, 5b, and 6b.