Intramolecular Ketene Cycloadditions. Synthesis of Isoflavones and 3-Aroylbenzofurans

Article abstract of DOI:10.1021/jo00242a002

The conversion of 2-(carboxyalkoxy)benzils to the corresponding phenoxyketenes to an intramolecular <2+2> ketene cycloaddition to ultimately yield isoflavones and/or 3-aroylbenzofurans.The ketenes may be generated by the classical dehydrochlorination of the acid chloride or by using Perkin reaction conditions, sodium acetate in refluxing acetic anhydride.The initial cycloaddition products are the corresponding β-lactones, which may decarboxylate to the isolated isoflavones and/or 2-aroylbenzofurans.The product distributions are dependent upon the substitution pattern in the orginal benzil acids.