Reaction of p-Hydroxycinnamyl Alcohols with Transition Metal Salts. 2. Preparation of Guaiacyl/Syringyl Di-, Tri-, and Tetralignols

Treatment of coniferyl alcohol (CA), sinapyl alcohol (SA), and their mixtures with copper or manganese salts yielded nine dilignols, five trilignols, and one tetralignol. The lignols were composed of guaiacyl (G) or CA units and syringyl (S) or SA units linked together by β-O-4 (b), β-5 (c for coumaran), β–β (r for resinol), and/or a novel γ-β (gb) linkage. None of the isolated lignols contained 5–5′ (biphenyl), 4-O-5, or β-1 linkages. Spectral analysis (¹H NMR, ¹³C NMR, MS) and comparison with authentic compounds confirmed the structures of the dilignols as G-b-CA, G-b-SA, S-b-CA, S-b-SA, G-c-CA, S-c-CA, G-r-G, G-r-S, and S-r-S; the trilignols as G-b-S-r-S, G-b-S-c-CA, S–b-S-r-S, and G-c-G-gb-G; and the only tetralignol as G-b-S-r-S-b-G.