The general ethoxalylation procedure for the synthesis of isoflavones has been applied to the synthesis of irigenin (VII) and tectorigenin (XVI). This synthetic route also yields the isomers, ψ-irigenin (XI) and ψ-tectorigenin (XX). Information concerning the product ratio in certain ethoxalylation reactions and the relative thermodynamic stabilities of 5,6,7- and 5,7,8-trisubstituted isoflavones is discussed.