Prenyloxycoumarins and prenyloxyfuranocoumarins (isopentenyloxy-, geranyloxy-, linear and cyclic sesquiterpenyloxy compounds and their biosynthetic derivatives) represent a family of secondary metabolites that have been considered for years just as intermediates of other coumarin-based compounds. Only in the last two decades these secondary metabolites have been recognized as interesting and valuable biologically active natural products. Up to now more than 160 compounds have been isolated from plants mainly belonging to the families of Rutaceae and Umbelliferae, comprising common edible vegetables and fruits like lemons, oranges and grapefruits. In view of the biological activity of some natural prenyloxycoumarins, very recently syntheses of structurally related analogs aimed to establish detailed structure-activity relationships have also been carried out. Many of the isolated prenyloxy- and prenyloxyfuranocoumarins and their semisynthetic derivatives were shown to exert in vitro and in vivo remarkable antitumoral, anti-inflammatory and anti-viral effects. The object of this review is to examine in detail the different types of prenyloxycoumarins and prenyloxyfuranocoumarins from the chemical, phytochemical and biological point of view.

Differently substituted benzimidazoles have been synthesised in very good yields in solvent-free conditions from o-phenylenediamine and aldehydes in the presence of Yb(OTf)₃ as catalyst. The method is applicable to aromatic, unsaturated and ­aliphatic aldehydes and to substituted o-phenylenediamines without significant differences.