Abstract
Syntheses of Moniliformin, a Mycotoxine with a Cyclobutenedione StructureSix different routes to 3‐hydroxy‐3‐cyclobutene‐1, 2‐dione (4), the free acid of the mycotoxine Moniliformin (=alkali salt of 4) are described. A common feature of all pathways is the synthesis of cyclobutanes having the oxidation level 6. Moniliformin precursors which are easily transformed to 4 by acid catalysed hydrolysis include [2+2]‐cycloadducts of ketene with tetraalkoxy‐olefins, 3,4,4‐trialkoxycyclobutenes, derivatives of polyfluorinated cyclobutenes, the brominated [2+2]‐cycloadduct of ethyl vinyl ether and dichloroketene, tetrabromocyclobutanone, [2+2]‐photocycloadducts of dichlorovinylenecarbonate with dichloroethylenes, and the dimer of chloroketene. The most convenient synthesis via the [2+2]‐cycloadduct of tetraethoxyethylene and ketene (14b) is reported in detail and produces 4 in four simple steps in 57% overall yield. In addition, two new syntheses of squaric acid (56) are described.
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