No abstract

Multistep Redox Systems. 1,3-Dimethylidenecyclobutanes Substituted by n-Systems: Syntheses and PropertiesAs potential redox systems 1,3-dimethylidenecyclobutanes are synthesized in which the 'em'-methylidene group participates in a cyclopentadienyl (type C4) or cycloheptatrienyl (type A5) system. Benzo-annellated systems are also described. The formation of the C=C bond by the reaction of thioketones (3 and 31) with diazo compounds is extended to 1, 6, 7, 21, and 24, which so far had not been employed. In some cases, intermediate thiiranes can be isolated (e.g. 4) which are smoothly transformed into the target compounds of types C4 and A5 by extrusion of sulfur. The new C=C bonds may be introduced stepwise, thereby allowing the synthesis of unsymmetrically substituted 1,3-dimethylidenecyclobutanes (eg. 20 and 35). Reduction of 10 by Na does not produce bicyclobutanes but compounds 43 and 44 with one dihydrofulvene unit. Es lag daher nahe, die in Heterocyclen eingebauten (Al, A2) oder chinoid-artigen (C3) Methyliden-Gruppen durch in Carbocyclen eingebaute zu ersetzen, die beim moglichen Ubergang in das Bicyclobutan-System genugend Aromatisierungsenergie gewin- Einleitung

Starting from bulk chemicals, novel isoxazoledicarboxylic acid esters were prepared and converted to the corresponding dicarboxylic acid monoamides in a few reaction steps and in high overall yields. Key intermediates for the cycloaddition step were chlorooximinoacetates or amides as nitrile oxide equivalents, prepared in one-pot reactions from diketene or acetoacetic acid esters. Isoxazoledicarboxylic acid monoamides combined good herbicidal activity with chemical flexibility. They were characterized as inhibitors of photosynthesis. Particularly, they affected the photosynthetic electron transport in photosystem I1 and the rate of carbon dioxide assimilation. Applied postemergence, the new compounds were found to control a broad spectrum of key weeds in corn. Excellent activity was found on Abutilon theophrasti (L.) Medik., Amaranthus retrojlexus L., Chenopodium album L., Ipomoea spp., Polygonum persicaria L., Solanum nigrum L. and Xanthium strumarium L. with rates between 0.2 and 0.5 kg ha-'. As a side-effect, the compounds also showed activity against grass weeds. The compounds are excellent tank-mix partners, e.g. for sulfonylureas, to complete the weed spectrum (Chenopodium album L., Solanum nigrum L.) and/or to reduce the risk of developing herbicide-resistant weeds.

158ChemInform Abstract The bisquinone methide cyclobutanes (III) and (V) are synthesized by coupling the corresponding diazo compounds (I) or (IV) with the cyclobutanedithiones (II). Reduction of (III) or (V) with sodium produces di(oxyaryl)bicyclobutanes which are trapped as the silyl ethers (VI) or (VII).

Reaction of the dithione (II) with the diazo compounds (Ia) or (Ib) gives the isolable thiiranes (IIIa), (IIIb) (cis/trans mixtures), which are then converted to the title systems (IVa), (IVb) by extrusion of sulfur.