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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.

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Rearrangement of a-Halogen-to a '-Halogen-cyclobutanones, Key Step of a Highly VersatileSynthesis of Pyrethroids Summary a-Halogenocyclobutanones, which are readily available by [2 + 21-cycloaddition of haloketenes to terminal olefins (e. g . 5 + 6), undergo an efficient and stereoselective cine-rearrangement to a'-halogenocyclobutanones in the presence of catalysts such as tertiary amines, HX acids or quaternary ammonium salts (e. g . 6 -+ 7, Table I). Preparative as well as mechanistic aspects of the cine-rearrangement are discussed. The 2,4-cis-disubstituted cyclobutanones 7-32 thus formed represent valuable intermediates in a new synthesis of pyrethroids 1. The X-ray structure of 2-chloro-4-(2,2,2-trichloroethyl)-3,3-dimethylcyclobutanone (7), the most important precursor of cis-3 (X = Cl) shows the following features : a puckered cyclobutanone ring (dihedral angle 3 I O), 2,4-cis-di-pseudoequatorial arrangement of the chloro and trichloroethyl substituents, and an endo-deviation (0.225 A; 11") of the carbonyl 0-atom from the plane formed by C( l), C(2) and C(4) (Fig. 2).

Me 15 (357;) Verhaltnis ' 85 : 15. 17 koiinte in Sproz. Ausbeute isoliert werden; weitere Reaktionsprodukte (> 0,2%) liessen sicli gas-chromatographisch nicht nachweisen. 16 17 (SO,;) A logoy: + B with thc constants A = 0.788 and B = 0,108 and a correlation coefficient of 0.983.Introduction. -Bimolecular reactions between anionic nucleophiles and neutral substrates are known to be accelerated by several orders of magnitude in certain dipolar aprotic compared with protic solvents [l] [ Z ] . Two factors must be considered