Flavan derivatives. XIII. The formation of 1,3-Diarylpropan-2-ols and 2,3-Diarylpropan-1-ols from Flavan-3-ols

Abstract

No change in specific rotation of (-)-1-(3,4-dimethoxyphenyl)-3-(2,4,6- trimethoxyphenyl)propan-2-ol was observed during attempted resolution, so that the propanol is probably close to optical purity in spite of its low specific rotation. (-)-Epigallocatechin pentamethyl ether was reduced with sodium and liquid ammonia to an analogous hexamethoxydiarylpropan-2-ol. Several conditions for reducing ( +)-catechin tetramethyl ether with lithium aluminium hydride-aluminium chloride mixtures were examined, and the reduction method was applied to (-)- epiafzelechin trimethyl ether and to (-)-epigallocatechin pentamethyl ether. The mechanism of formation of the (-)-2,3-diarylpropan-1-ol from (+)-catechin and (-)-epicatechin tetramethyl ethers is discussed. The 5,7,4'-trimethyl ethers of (-)-epiafzelechin and (±)-dihydrokaempferol were found to form a 1 : 1 molecular complex.