Synthesis of some new benzofuran‐based thiophene, 1,3‐oxathiole and 1,3,4‐oxa(thia)diazole derivatives

Treatment of 3‐(3‐methylbenzofuran‐2‐yl)‐3‐oxopropanenitrile (1) with phenyl isothiocyanate afforded the thioacetanilide derivative 3, which when reacted with α‐haloketones, α‐halodiketones, and hydrazonoyl chlorides gives thiophene, 1,3‐oxathiole, and 1,3,4‐thiadiazole derivatives 6a,b, 10a,b and 14a–g, respectively. Treatment of 3‐methyl‐2‐benzofurancarboxylic acid hydrazide (15) with benzaldehyde followed by bromine afforded the 1,3,4‐oxadiazole derivative 18. Treatment of the acid hydrazide 15 with phenyl isothiocyanate gave the thiosemicarbazide 20. Compound 20 could be converted into 1,3,4‐oxadiazole, 1,2,4‐triazole‐3‐thione, and 1,3,4‐thiadiazole derivatives 21, 22, and 23, respectively.