A parallel orientation between the coordinated substrate enolate and a face‐on naphthyl group of the TADDOL ligand (see picture; Ti dark gray, O red, Cl green, F orange, N violet) control the stereochemical outcome of the Ti‐catalyzed asymmetric fluorination of 1,3‐dicarbonyl compounds with 1‐chloromethyl‐4‐fluoro‐1,4‐diazoniabicyclo[2.2.2]octanetriethylenediamine (F‐TEDA; its approach is also shown the in picture). Density functional theory based quantum‐mechanical molecular mechanical calculations also disclose the fluorine‐transfer step as occurring by a single‐electron transfer.

No abstract

Septoria nodorum (wheat glume blotch). We also confirmed their mode of action as inhibition of mitochondrial respiration at complex III in beef heart and the model fungus Neurospora crassa.With their novel structures, interesting mode of action and significant fungicidal activity, the crocacins were attractive leads for synthesis, although ambitious targets as agrochemicals due to their relatively complex structures. We therefore decided to embark on a programme of chemistry to see if simpler, more active and more stable compounds could be found.For practical use on crops in the field, fungicides must have reasonable stability on leaf surfaces so that they can kill incoming fungal spores over a period of 1-2 weeks as well as those that are already present. Both crocacin A (1) and D (4) were shown to have low levels of photostability, with 50% of the parent compound being lost in 7 and 37 min, respectively, as thin films on glass slides in a simulated sunlight test in the laboratory. This low photostability is not surprising in view of the number of double bonds the crocacins contain, and would undoubtedly lead to very poor persistence of fungicidal activity on plants, severely limiting the activity that these compounds could show in the field.There was no significant aqueous hydrolysis of the glycine methyl ester group of crocacin A (1) at pH 4 and 7 at 39 o C, but addition of pig liver esterase under these CROP PROTECTION RESEARCH 685Abstract: A short route to the synthesis of analogues of the antifungal but unstable natural product crocacin D was developed. A wide range of compounds were made in which the complex side chain was replaced by simple aromatic units, and many of them showed high activity in a mitochondrial beef heart respiration assay. Some of these compounds were active against plant pathogenic fungi of agricultural importance in glasshouse tests. In order to find compounds with greater stability than the natural crocacins, the photolabile (Z)-enamide was replaced with many different moieties, but none gave rise to useful fungicidal activity.

No abstract

Catalytic fluorination/chlorination competition experiments of β‐keto ester 5 were used to assess the relative fluorinating activity of various electrophilic NF reagents (containing an NF bond). Thus, in the halogenation reactions catalyzed by the [Ti(TADDOLato)] complex 1 (=bis(acetonitrile)dichloro[(4R,5R)‐2,2‐dimethyl‐α,α,α′,α′‐tetra(naphthalen‐1‐yl)‐1,3‐dioxolane‐4,5‐dimethanolato(2−)‐κO,κO′]titanium), the activity range of a series of commercially available reagents spans more than two orders of magnitude. SelectfluorTM (=1‐(chloromethyl)‐4‐fluoro‐1,4‐diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate); 9; also called F‐TEDA; TEDA=triethylenediamine) reacts more than 100 times faster than 1‐fluoropyridinium tetrafluoroborate.