A new synthesis of ( Z)-coniferyl alcohol, and characterization of its derived synthetic lignin

Abstract

The ( Z)-monolignols (hydroxycinnamyl alcohols) are found along with their predominant ( E)-isomers in a number of plants. Their role in lignification is unknown. A new synthetic route to ( Z)-coniferyl alcohol has been developed via Still and Gennari's modification of the Horner-Emmons olefination to produce ( Z)-unsaturated esters. Although previous studies have shown that ( Z)-coniferyl alcohol will polymerize by single-electron (radical) processes to produce synthetic lignins, the stereochemistry of units in the resulting structure had not been addressed. NMR analysis of a synthetic lignin from ( Z)-coniferyl a alcohol indicates 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 these synthetic lignins provides the necessary database for more careful examination of real plant lignins.