Acid-catalyzed rearrangements of flavan-4-phloroglucinol derivatives to novel 6-hydroxyphenyl-6a,llb-dihydro-6H-[1]benzofuro[2,3-c]-chromenes and hydroxyphenyl-3,2'-spirobi[dihydro[l]benzofurans]

Abstract

Acetic acid-catalyzed cleavage of proanthocyanidins in the presence of phloroglucinol gives a series of 2R procyanidin- and prodelphinidin-phloroglucinol adducts together with a novel 2S all-cis derivative implicating cleavage of the pyran ring and subsequent inversion of stereochernistry at C-2c. These flavan-4-phloroglucinol adducts also suffer dehydration to products with novel fused dihydrobenzopyr and ihydrobenzofuran rings. In addition, cleavage of the flavan C-10A-C-4c bond followed by dehydration results in unique 3,2'-spirobi[dihydro[l]benzofurans].

Citation

Steynberg, Petrus J.; Steynberg, Jan P.; Hemingway, Richard W.; Ferreira, Daneel; McGraw, G. Wayne. 1997. Acid-catalyzed rearrangements of flavan-4-phloroglucinol derivatives to novel 6-hydroxyphenyl-6a,llb-dihydro-6H-[1]benzofuro[2,3-c]-chromenes and hydroxyphenyl-3,2''-spirobi[dihydro[l]benzofurans]. Journal of Chemical Society, Perkin Transactions I. 2395-2403.