Synthesis of Proanthocyanidins. Part 1. The First Oxidative Formation of the Interflavanyl Bond in Procyanidins.

[摘要]：A novel and efficient method for the oxidative condensation of tetra-O-methyl-3-oxocatechin (I) with tetra-O-methylcatechin (II) is described. Treatment of a soln. of II (2 equiv) and I (1 equiv) with silver tetrafluoroborate readily affords the phenolic per-O-Me ethers of 3-oxocatechin(4-8)-catechin III (R = a-H) and III (R = b-H). Subsequent metal hydride redn. provides access to procyanidin B-3 analogs with the 3,4-cis diastereomers predominating.

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