A new Knoevenagel-type synthesis of fully substituted γ-hydroxybutenolides

The synthesis of fully substituted γ-hydroxybutenolides is possible by a Knoevenagel-type ring condensation of α-methyleneketones and α-ketoesters under basic conditions. This novel transformation allowed the preparation of di-aryl/heteroaryl substituted hydroxyfuranones, such as 20 and 27, which are important intermediates for pyridazine fungicides. As it turned out, a whole range of different substituents, such as alkyl, cycloalkyl, aryl, heteroaryl and ester groups could be linked to the butenolide scaffold, demonstrating the broad scope of the novel cyclization.