Syntheses of Monilifonnin, a Mycotoxine with a Cyclobutenedione Structure
SummarySix 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. and produces 4 in four simple steps in 57% overall yield. In addition, two new syntheses of squaric acid (56) are described.