A NEW SYNTHESIS OF (Z)-CONIFERYL ALCOHOL, AND CHARACTERIZATION OF ITSDERIVED SYNTHETIC LIGNIN

The (Z)-monolignols (hydroxycinnamyl alcohols) are found along with th eir predominant (E)-isomers in a number of plants. Their role in ligni fication is unknown. A new synthetic route to (Z)-coniferyl alcohol ha s been developed via Still and Gennari's modification of the Horner-Em mons olefination to produce (Z)-unsaturated esters. Although previous studies have shown that (Z)-coniferyl alcohol will polymerize by singl e-electron (radical) processes to produce synthetic lignins, the stere ochemistry of units in the resulting structure had not been addressed. NMR analysis of a synthetic lignin from (Z)-coniferyl alcohol indicat es that unsaturated sidechains in the resulting lignin retain their (Z )-geometry. Other structures are altered in their relative proportions but retain the same stereochemistry. Assignment of structures in thes e synthetic lignins provides the necessary database for more careful e xamination of real plant lignins. Published by Elsevier Science Ltd.