Dimeric and trimeric flavonoids containing a cyclopentane ring: 6,7-diaryl-6a,7,13,13a-tetrahydro-6H-7,13-methano[1]benzopyrano[3,4-c][1]benzoxepins

Abstract

4,4′-Biflav-2-enes react with electrophiles in the presence of alcohols, yielding substituted 6,7-diaryl-6a,7,13,13a-tetrahydro-6H-7,13-methano[1]benzopyrano[3,4-c][1]benzoxepins, e.g.(6)–(15). The structures and stereochemistries of these compounds have been deduced from their conversion into other analogues, e.g.(18)–(21), and from n.m.r. studies.

Trimeric flavonoids (23) and (24) containing the benzoxepin structure have been synthesised by the reaction of flavylium perchlorate with 4,4′-biflav-2-ene and alcohols. The structures of the trimers are not in any serious doubt but their stereochemistries are not fully known.