Acid-catalyzed rearrangements of flavan4phlorogkinol derivatives to novel 6=hydroxyp@nyMa, 11 bdihydro=M-[ 1 ]benzofuro[2,3-c ]- chromenes and hydroxyphenyl=3,2’-spirobi[dihydro[l]benzofurans] Petzvs J. Steynberg, ** Jan R Steynberg,’ Rhhrd W. Hemingway,*@ Daneel Ferreira” and G. Wayne McGraw’ a Southern Research Station, USDA Forest Service, Pineville, LA 71360, USA b Department of Chemistry, University of the Orange Free State, Bloemfontein, 9300, South Africa ’ Department of Chemistry, Louisiana College, Pineville, LA 71360, USA Acetic acid-catalyxed cleavage of proanthocyanidins in the preaeace of phloroglucinol gives a series of 2R procyanidln- and prodelphfnidin-phIoroglucino~ adducta together with a novel 2s skis derivative implicating cleavage of the pyran ring and subsequent imersion of stereochemistry at C&. These Bavan- 4-phloroglucinoi adducta also suffer dehydration to producb with novel fused dihydro&ozopyran- dihydrohcnaofuran ringa. In addition, cleavage of the &wan C-10,4Xc bond followed by dehydration . . results In unique 3,2’aphwbi@ihyd&~ofurans~. The thesis that the interflavanyl bond of polymeric procyani- dins and prodelphinidins can be cleaved and chain extender units rccovercd (without invtrsion of stereochemistry at C-2&, as first advanced by Scars and Casebier’ and refined by Brown and Shaw,’ has led to routine use of acid-catalyxcd cleavage in the presence of thiols or phloroglucinol as capture nuclcophilu in the characterization of the 5,7dihydroxypolyflavanoids (Scheme I).’ Because of the power of these reactions in d&ring the constituent units in polymeric &dins and prodtlphi- nidins, acid-catalyzed cleavage reactions have been exploited as a ‘quantitative’ analytical approach to a definition of the the strut- strut- ture of condensed tannin poiymara” However, wc have con- sistently failed to obtain quantitative yields of tlavan4thiol or phloroglucinol adducts from acetic acid-cam&& ckavage of condensed tannina*’ This problem promptad !Mher study of the products of acetic acid- cleavage of these tannins with particular emphasis on ddGng the marranlpmmu that might occur when reactions at 1OO’c am extended to 24 h or more Rearrangement products with the novtl title htttrocyciic ring structures w obtained. Pecan (Curuyfa ifkmuis) rmt pith calatiNta an WXptiOnahy rich source of condensed tannins with poteotial for use in lea- ther manufacture adhesives and other speciality chemicals based on wwwabk IWO- Preview wrk oo the condensed tannins from pecan nut pith indicated that these polymers were ma& up of 3,3’,4’.5,5’,7-hexahydroxy&vans (R -OH, pro- delphinidins) and 3.3’.4’.S.7-pcntahydroxygavans (R = H. procyanidins) in relative pmportha of about 6: 1 (Scheme I).‘ The chain extender units were made up of approximately equal proportions of 2.3~tram (ic C-ring) and 2.3-&r (ic F-ring) flavan-Eola Both cat&in (H-ring, R = H) and gallocatcchin (H-ring, R = OH) but no 2,3-c& (ic I-ring) &van-3-01s ore isolated as terminal unit cieava* producta In the present work, pecan nut pith tannins u5rc mactcd with phloroglucinol and acetic acid at 100°C for 24 or 48 h. After mtthylation and acetylation of the products, a series of pro- anthocyanidin derivatives including the known methyl ether -2000 V 210 230 250 no 290 310 330 350 370 A/nm Ftg.1 CDrpectmof(u)2,(b)I.(c)l4and(d)4 acetate derivatives epicatechin-(4g - 2)_phloroglucinol t 1, epigallocatechin-(4g w t)_phloroglucinol 2, catcchin- (4a -_, 2>phloroglucinol 3, gallocatcchin-(4a -+ 2)_ pbloroglucinol 4 and gallocatcchin-(4g + 2)-phloroglucinol 5 were isolated. The methyl ether acetate derivatives catcchin 6 and gallocatechin 7 were also isolated but no 2,3-cis flavan-3-01s representing the terminal units were rccovercd from cleavage of the polymer as was noted in a study of the acetate derivatives of products of thiolytic cleavage, where the pcracctatt derivatives 8 and 9 were obtained.’ ‘H NMR (Tab& I), “C NMR (Table 2) and CD spectral data (Fig. 1) provided the evidence needed for deli&ion of the struc- turn of the pbloroglucind addum obtained from the reaction of pecan tannins with pNoroglucinol. The nlativt proportions of these products w5re consistent with the results obtained when pecan pith tannins were reacted in the prcscncc of toluene-a&ioJ.’ A&r acetylation, the major products of thi- olysis were the peracctate derivatives catcchin_4a-hcnxyl sulfide 10, ga&xatcchirMa-benzynzyl sulfide 11. epicatechin+hen@ 7 Numbering of the phloroglucinol D-ring in compounds 1-5 and I4 retains the numbering of phloroglucinol and starts with a carbon carry- ing a hydroxy group.~ as to be consistent with the system for pro- anthocyanidins prvposai by Hemingway CI al.’