CONDENSED TANNINS - THE FORMATION OF A DIARYLPROPANOL-CATECHINIC ACID DIMER FROM BASE-CATALYZED REACTIONS OF (+)-CATECHIN

Reaction of (+)-catechin at pH 12 and 40-degrees-C results in the stereoselective (if not stereospecific) formation of an enolic form of 1-[6-(3',4'-dihydroxyphenyl)-7-hydroxybicyclo[3.3.1]nonane-2,4,9-trione-3-yl] -1-(3,4-dihyroxyphenyl)-3-(2,-4,6-trihydroxyphenyl)-propan-2-ol. The n.m.r. chemical shift assignments determined by a variety of two-dimensional experiments permit a conclusion that the compound is one of four diastereoisomers possible from reaction of the two quinone methide intermediates. Stereoselectivity in the formation of this compound can be accounted for by preference for Re-face attack on both 2-C's of the quinone methides involved in the formation of the molecule.