No abstract

: Systemic Acquired Resistance (SAR) is an inducible resistance mechanism in plants that, together with other defence mechanisms, provides broadspectrum and long-lasting disease control. With novel screening techniques the benzo[1,2,3]thiadiazole-7-carboxylic acid derivatives have been identiÐed as a new class of chemicals which stimulate the plantÏs own defence mechanisms. The synthesis and biological activities of various benzo[1,2,3]thiadiazoles and related structures are described. S-Methyl benzo[1,2,3]thiadiazole-7-carbothioate is the Ðrst synthetic chemical "plant activatorÏ that has been developed for this novel disease control concept.

The X‐ray structures of fifteen 1, 3‐imidazolidine, 1, 3‐oxazolidine, 1, 3‐dioxan‐4‐one, and hydropyrimidine‐4(1H)‐one derivatives are described (Table 2) and compared with known structures of similar compounds (Figs. 1–20). The differences between structures containing exocyclic N‐acyl groups and those lacking this structural element arise from the A1,3 effect of the amide moieties. Even t‐Bu groups are forced into axial positions of six‐ring half‐chair or into flag‐pole positions of six‐ring twist‐boat conformers by this effect (Figs. 16–20). In the N‐acylated five‐membered heterocycles, a combination of ring strain and A1, 3 strain leads to strong pyramidalizations of the amide N‐atoms (Table 1) such that the acyl groups wind up on one side and the other substituents on the opposite side of the rings (Figs. 4–9 and Scheme 3). Thus, the acyl (protecting!) groups strongly contribute to the steric bias between the two faces of the rings. Observed, at first glance surprizing stereoselectivities of reactions of these heterocycles (Schemes 1 and 2) are interpreted (Scheme 3) as an indirect consequence of the amide A1, 3 strain effect. The conclusions drawn are considered relvant for a better understanding of the ever increasing role which amide groups play in stereoselective syntheses.

Under 'non-fermenting' conditions, i.e. in tap water, in the absence of nutrients, baker's yeast (25-380 g/g of substrate, aerobic) reducesb-keto esters such as those mentioned in the title with better selectivity than under the normally employed 'fermenting' conditions (sugar and nutrients, CO, development). With the B-keto esters containing the tetralone substructure, large amounts of yeast are required (250-380 g/g); the substrate disappears in the biomass, and the desired reduction product can be extracted after reaction times of up to a week at 30'. The configurations of most products (16-24) is established. Generally, the (R)-b-keto ester is reduced faster than the (S)-enantiomer (the two esters are in equilibrium under the reaction conditions), and the hydride transfer takes place preferentially from the diastereotopic Re-face. The B-hydroxy esters thus available are useful starting materials for syntheses of enantiomerically pure compounds (EPC). ') 2, ' ) 4,Ausfuhrliche Ubersichtsartikel uber Hefe-Reduktionen: 11-41, Teil der Doktorarbeit von S. R.

The biological potential of pinoxaden and its active principle pinoxaden dione in terms of grass weed control and tolerance in cereals was fully exploited by inclusion of the safener cloquintocet-mexyl in the formulation in combination with a specific and tailor-made tank-mix adjuvant based on methylated rape seed oil.