Lignin Chromophores. III. Syntheses of Hydroxy- and Alkoxystilbenes via Aryl Migration

Abstract

Stilbenes, representing stilbenoid structures present in residual lignins, have been synthesized by condensation of monochloroacetaldehyde diethylacetal with appropriate phenols and phenol ethers, followed by alkali- or acid-promoted rearrangement of the resulting 1,1-diaryl-2-chloroethanes. It is proposed that the mechanism of these rearrangement steps involves aryl migration with formation of intermediates of the spiro-cyclohexadienone type. The yields of individual stilbenes vary within wide ranges and are in certain cases moderate. However, the method is competitive due to its simplicity and the availability of the starting materials required.