Benzimidazole continued 2-

When benzimidazoles are abused, resistance is likely to occur and often has. However, when used judiciously as part of well considered strategies, benzimidazoles continue to give excellent control. Mixtures and combinations of mixtures and alternations with multi-site contact fungicides have proved very effective, especially if used before problems become apparent. 

Polybenzaylene benzimidazoles (pyrrones) Thermally stable to 600° C (1,112°F) insoluble in common solvents good mechanical properties. (Continues)... 

Current single-mode continuous-flow microwave reactors allow the processing of comparatively small volumes. Much larger volumes can be processed in continuous-flow reactors that are housed inside a multimode microwave system. In a 2001 publication, Shieh and coworkers described the methylation of phenols, indoles, and benzimidazoles with dimethyl carbonate under continuous-flow microwave conditions using a Milestone ETHOS-CFR reactor (see Fig. 3.11) [104]. In a typical procedure, a solution containing the substrate, dimethyl carbonate, 1,8-diazabicy-clo[5.4.0]undec-7-ene (DBU) base, tetrabutylammonium iodide (TBAI), and a solvent was circulated by a pump through the microwave reactor, which was preheated to 160 °C and 20 bar by microwave irradiation (Scheme 4.31). Under these condi-... 

Scheme 4.31 Methylation of phenols, indoles, and benzimidazoles in a multimode continuous-flow microwave reactor.

Major advancements in the chemistry of pyrazoles, imidazoles, triazoles, tetrazoles, and related fused heterocyclic derivatives continued in 2000. Solid-phase combinatorial chemistry of pyrazoles and benzimidazoles has been particularly active. Synthetic routes to all areas continue to be pursued vigorously with improvements and applications. Notably, metal-promoted and cross-coupling reactions of all classes seemed to be a dominant theme in 2000. Applications of pyrazole-, imidazole-, and 1,2,3-benzotriazole-containing reagents to a wide array of synthetic applications remained active. 

The same effect is observed for the substituted pyridyl-pyrazole and -imidazole systems. While 2-(pyrazol-l-yl)pyridine 24 gives a low spin iron(II) complex a continuous spin transition is observed centred just above room temperature in solid salts of [Fe (31)3]2+ and just below in solution [39]. Spin crossover occurs in the [Fe N6]2+ derivative of 2-(pyridin-2-yl)benzimidazole 32 (Dq(Ni2+)=1050 cm"1) but not in that of the 6-methyl-pyridyl system 33 (Dq(Ni2+)=1000 cm"1). Although the transition in salts of [Fe 323]2+ is strongly influenced by the nature of the anion and the extent of hydration, suggesting an influence of hydrogen-bonding, in all instances it is continuous [40]. 

Due to the biological significance of some azoles (pyrrole, indole, imidazole, benzimidazole) and the consequences of acid-base equilibria in their functions, a continuous interest in the behavior in water is to be expected. To quote a significant approach, imidazole is being used to determine the intra- and extracellular acidity by H-NMR (82MI4 86UP13). 

A mixture of 4-[4-(diphenylmethyl)-l-piperazinylmethyl]-Nl-ethyl-l,2-benzenediamine and acetic acid is stirred at room temperature till all solid enters solution. Then there are added pentyl ethanimidate hydrochloride and stirring is continued first for 1 h at room temperature and further for 1 h at reflux. The reaction mixture is evaporated and the residue is stirred in water. The whole is alkalized with a sodium hydroxide solution and the product is extracted with dichloromethane. The extract is dried, filtered and evaporated. The residue is purified by column-chromatography over silica gel using a mixture of trichloromethane and methanol as eluent. The pure fractions are collected and the eluent is evaporated. The product is filtered off and dried, yielding 5-[4-(diphenylmethyl)-l-piperazinylmethyl]-l-ethyl-2-butyl-lH-benzimidazole melting point 124.8°C (crystallized from 4-methyl-2-pentanone). 

Methoxy-2-[(3,5-dimethyl-4-nitro-2-pyridinyl)methylthio]-lH-benzimidazole(50 g, 0.145 mole) was dissolved in methanol and heated to 45°C. A solution of sodium methoxide (50 g, 0.925 mole) in methanol (150 ml) was added dropwise over a period of 3 hours at 45°-60°C. Stirring was continued for another 2 hours and then methanol was distilled off under reduced pressure. To the cooled residue was added water (200 ml) followed by concentrated HCI (65 ml) until the pH of the mixture was 7.5. The reaction mixture was extracted with dichloromethane and the dichloromethane layer was washed with water (2 times 100 ml). The dichloromethane layer was dried over sodium sulfate and concentrated to yield the product as an amber color syrup. Yield was 40.1 gm, about 83.8% of theoretical. A solid sample was obtained by trituration of the syrup several times with petroleum ether. Melting point was 87°-90°C. 

Benzimidazole fungicides (Figure 1) are in wide use, as they are highly effective against various diseases present in commercially important crops. However, the intense, continuous use of... 

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