ABSTRACT
Many naturally occurring oxidative dimers of various C6.C3-phenols encompassing a benzofuranoid moiety have been discovered. Although details concerning their biosynthetic origin remain to be clarified, it seems probable that their monomeric units are based on cinnamic acids, cinnamyl alcohols, propenylphenols, and allylphenols as alternative monomeric starting materials. The present review is restricted to another group of such compounds, namely, oxidative dimers of propenylphenols plus allylphenols, which are, among the several groups of coupling products, certainly the most interesting ones. Natural distribution, structural comparison, reactivity and even synthesis of propenyl-phenol plus allylphenol derived neolignans are studied more conveniently through a biogenetic system of classification. A neat distinction between rearranged neolignans primarily derived by 8.1' coupling and neolignans derived by direct 8.3' coupling results by the comparison of the oxygenation pattern of their allylphenol derived moieties with the oxygenation pattern of the eugenol type precursor.
