An unexpected skeletal transformation of 1,4-dihydroxythioxanthen-9-one on treatment with iodic acid: the first construction of the 2-(5-oxofuran-2-ylidene)-1-benzothienyl-3-one core

Treatment of 1,4-dihydroxythioxanthen-9-one with iodic acid gives, depending on the reaction conditions, predominantly either thioxanthen-1,4,9-trione or, unexpectedly, 2-(5-oxofuran-2(5H)-yliden)-1-benzothienyl-3(2H)-one. The latter is obtained in 60% yield.