Electrophilic aromatic substitution of catechins: bromination and benzylation

Relative yields of C-6, C-8, and C-6 and C-8 substituted catechins obtained from the reaction of (+)-catechin or 3′,4′,5,7-tetra-O-methyl-(+)-catechin with pyridinium hydrobromide–perbromide, bromine, p-hydroxybenzyl alcohol, or o-hydroxybenzyl alcohol showed differing selectivities depending upon the electrophile used. Ratios of C-6 to C-8 substituted products were 1:1.2 for the reaction of p-hydroxybenzyl alcohol with (+)-catechin, 1 : 2–3 for reaction of either bromine or o-hydroxybenzyl alcohol with (+)-catechin, and essentially exclusive substitution at the C-8 position in the reaction of tetra-O-methyl-(+)-catechin with bromine. Comparatively high proportions of 6-substituted and 6- and 8-disubstituted products were obtained in the reaction of (+)-catechin with one equivalent of either p- or o-hydroxybenzyl alcohol.