Summary Six 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+ 21-cycloadducts of ketene with tetraalkoxy-olefins, 3, 4, 4-trial koxycyclobutenes, derivatives of ...