The pyrethrins and related compounds. Part XII. 5-Substituted 3-furoates and 3-thenoates, intermediates for synthesis of insecticidal esters

Chloromethylation of 3-furoates, followed by a Friedel-Crafts reaction, gives 5-aralkyl-3-furoates. Such compounds and the corresponding 3-thenoates are more conveniently synthesised by condensing the ethylene acetals of 5-substituted levulinic esters with ethyl formate. The resulting 2-formyl-4-oxo-ester derivatives are cyclised directly by aqueous acids to give furans, and by phosphorus pentasulphide to give the corresponding thiophens.