SummaryMalonylmethyl radical I [. CH,CH(COOE:t),] and its thioester analogue I1 [. CH,CH(COOEt) (COSEt)] were generated by standard photolytic and thermolytic methods from perester and bromo precursors. The structures of I and I1 were examined by ESR spectroscopy and found to exist in preferred conformations. However, no indication for their rearrangement by 1,2-shift of either an ethoxycarboxyl or (ethylthio)carbonyl group to the corresponding succinyl radicals I11 and IV, respectively, was found at temperatures below -40 "C. At higher temperatures of up to 140 "C, the search for malonylmethyl -+ succinyl rearrangement was examined by thorough-product analysis of the perester decomposition. There is evidence for the rearrangement of the radical I to I11 by photolysis and of the radical I1 to IV by thermolysis at 130 "C in chlorobenzene to only a small extent.

Synthesis of the pure, bicyclic olefines Bicyclo[4.2.1]non‐2‐ene, Bicyclo[4.2.1]non‐3‐ene and Bicyclo[4.2.1]non‐7‐ene The synthesis of the olefines bicyclo[4.2.1]non‐2‐ene (3), bicyclo[4.2.1]non‐3‐ene (4) and bicyclo[4.2.1]non‐7‐ene (5) of high ‘certified’ purity from one common precursor (7) is described.

Die reversible Stabilisierung eines Bredt‐Olefins gelang erstmals mit einer Platin(0)‐Verbindung. Im Komplex (3) (Röntgen‐Strukturanalyse) hat das Olefin die gleiche Konformation wie freies (2) (Kraftfeldrechnungen). CS2 bildet aus dem Komplex isomerenfreies (2) zurück.

Reversible stabilization of a Bredt olefin has been accomplished for the first time with a platinum(0) compound. In complex (3) (X‐ray structure analysis) the olefin has the same conformation as free (2) (force field calculations). Treatment of the complex with CS2 regenerates isomer‐free (2).

The biological activity of a series of N‐(pyrid‐3‐yl)thioureas and ‐carbodiimides, analogues of the insecticide/acaricide diafenthiuron, towards the carmine spider mite (Tetranychus cinnabarinus Boisd.) and the two‐spotted spider mite (T. urticae Koch) was analysed using QSAR methodology. A canonical correlation analysis allowed for the establishment of a prediction model and the identification of outliers within that model. The chemodynamic behaviour of certain compounds in the two series, including these outliers, determined by using photochemical experiments in the laboratory as well as in the glasshouse, was shown to be responsible for anomalous results obtained in the biological tests. It was found from the above study that the biological activity towards both spider mite species is extremely sensitive to the kinetics of formation of the carbodiimides from the corresponding thioureas and to the photostability of the former. The results obtained with a thiourea which underwent no appreciable photochemical transformation into the corresponding carbodiimide supported the hypothesis that the thioureas are also in‐vivo propesticides of the acaricidal carbodiimides.