ACID-CATALYZED REARRANGEMENTS OF FLAVAN-4-PHLOROGLUCINOL DERIVATIVES TO NOVEL NYL-6A,11B-DIHYDRO-6H-[1]BENZOFURO[2,3-C]CHROMENES AND HYDROXYPHENYL-3,2'-SPIROBI[DIHYDRO[1]BENZOFURANS]

Acetic acid-catalyzed cleavage of proanthocyanidins in the presence of phloroglucinol gives a series of 2R procyanidin-and prodelphinidin-ph loroglucinol adducts together with a novel 2S all-cis derivative impli cating cleavage of the pyran ring and subsequent inversion of stereoch emistry at C-2(C), These flavan-4-phloroglucinol adducts also suffer d ehydration to products with novel fused dihydrobenzopyran-dihydrobenzo furan rings, In addition, cleavage of the flavan C-10(A)-C-4(C) bond f ollowed by dehydration results in unique 3,2'-spirobi[dihydro[1]benzof urans].