Benzimidazole requirements

Additional heterocycles, such as benzothiazole, benzoxa-zole, and 4,5-dimethylthiazole, could be alkylated. 1-Methyl-benzimidazole required higher catalyst and ligand loadings (10 mol% RhCl(coe)2]2, 15 mol% PCys). Multiple alkylations occurred for the purine substrate (eq 9). 

One-pot protocol for the synthesis of 2-(N-vinylpyrrol-2-yl)benzimidazoles requires air bubbling through a reaction mixture (DMSO, 70°C-80°C, 1 h). 

Due to the steric requirement of these substituents the formation of a columnar structure with infinite M M interactions is inhibited, and only the association of pairs of molecular units is allowed. The Ni Ni distance is 3.21 A [164]. If the same compound is crystallized in the presence of benzimidazole, the [Ni(dmg-BF2)2]2 dimer units are sandwiched between sheets of benzimidazole molecules due to n-n interactions resulting in an increased Ni Ni separation of 3.358 A [165]. With anthracene the n-n interactions seem to be stronger, because in this case the parent dimer molecule is cleaved. Each monomer now has a conformation of type B (Fig. 32) and is sandwiched by anthracene molecules [166]. Compound 121 has the same configuration [163d]. 

In analogy to the reaction of CDI with carboxylic acids, the even more reactive NJf -carbonyldi-1,2,4-triazole 5bl has been used instead of CDI in cases where specific structural effects require a higher reactivity of the azolide. On the other hand, the example of the last paragraph of the preceding section showed that A -carbonyldi-benzimidazole 151 141 and AyV -carbonyldibenzotriazole 151 have been useful for the syntheses of azolides with reduced reactivities when these are essential and sufficient for the specific reaction in question. 

Imidazolines are also formed in silver cyanide-catalyzed cyclization of alkyl isocyanides with aliphatic diamines (Scheme 103).169 This simple synthesis can be applied in a general way with difunctional nucleophiles and has been used to prepare benzimidazoles, oxazoles, thiazoles, and oxazines.169 It is suggested that transient carbene complexes are formed in these reactions (cf. 87 in Scheme 103) but further work is required to ascertain the mechanism and scope of these processes. 

Following the pioneering work by Alterman, several microwave-assisted palladium-catalyzed aminations have been reported for a number of different substrates, using different types of palladium sources and ligands. The examples shown in Scheme 6.59 include bromoquinolines [124], aryl triflates [125], and intramolecular aminations in the synthesis of benzimidazoles [126]. In all cases, the use of micro-wave irradiation dramatically reduced the required reaction times and in many cases also improved the yields. Several authors have also found that the microwave-driven reaction required significantly less catalyst than its conventionally heated counterpart [126]. 

A number of syntheses of heterocycles were performed using the MORE technique [17, 18]. While most of these reactions had been reported in Organic Synthesis to require reflux times of an hour or more, Bose et al. were able to obtain comparable yields in a matter of minutes. For example, benzimidazole 18 was synthesized from 1,2-diaminobenzene 17 and formic acid, which served as both reagent and solvent, in 70% yield in 3 min (Scheme 4.10), compared with the recommended heating time of 2 h [17]. 

Arylations of amines and nitrogen-containing heterocycles require the presence of a copper catalyst, usually 10% copper(ll) acetate. For example, the reaction of 4-MeC6H4Pb(OAc)3 with the benzimidazole 20 affords the arylation product 21 in 98% yield.39 40 Similarly, the arylation of the amino groups of heteroaromatic compounds 22 and 23 gives rise to the corresponding products 24a and 25 in good to excellent yields (Equations (7)-(9)).41 42... 

The two-phase alkylation reactions have been extended to the acylation of simple heteroaromatic systems. Generally, the required conditions are milder than those employed for the alkylation reactions, but an excess of the acylating agent is usually required, owing to its facile hydrolysis in the basic media. Thus, benzimidazole and its 2-alkyl and 2-aryl derivatives have been benzoylated [46], and pyrrole and indole have been converted into a range of A-acyl [47, 48] and A-sulphonyl derivatives [48-53] (Table 5.35 and Table 5.36). 

For systems containing two heteroatoms in the five-membered component the use of mixed (/-constants must be considered. These have been used for the correlation of pAVs of benzimidazoles for which (am + op) is required for the 5- and 6-substituted compounds and (a + oa) for the 4 and 7.383 This approach has been extended to the study of nucleophilic substitution in 2-chloro-7V-methylbenzimidazoles,384 385 2-... 

Application techniques can influence the efficacy of postharvest fungicides and, thus, alter the keeping quality of treated fruit. Application of sodium ortho-phenylphenate (SOPP) in a foam washer with an exposure time of only 15 to 20 sec is not as an effective method as a soak or drench treatment requiring 2-4 min (167). However, if proper pH control is not maintained, fruit may be burned with the soak or drench treatment (169, 170, 171). Applications of SOPP in wax were less phytotoxic (172). Within the last 14 years, development of the benzimidazoles, thiabendazole Q -(4 -thiazolyl) benzimidazole and. benoniyl Tmethyl 1-(butyl carbamoyl)-2-benzimidazole-carba-mat J, has led to the availability of fungicides with high... 

Polyacrylonitriles. An increasing proportion of the polyacrylonitrile fibers produced have a good basis white and do not require further bleaching [130,131], The use of FWAs that can be applied in the chlorite bleaching bath is therefore steadily declining. Suitable types include benzimidazoles such as 46-48. 

The need for new fungicides for stone fruits has increased because of the development of benzimidazole-resistant Monilinla fructicola (8,9,30) and Coccomyces hiemalls (10) in important stone fruit production areas of the eastern United States. Resistance has been a major problem for stone fruit growers because alternative fungicides are less effective, more costly or require more frequent applications than benzimidazole fungicides. The recent registrations of iprodione and triforine for control of stone fruit diseases have helped to alleviate problems caused by benzimidazole resistance. 

Oxidation is, of course, the dominant reaction. For example, vaporized trifluralin ( a, a, < -trifluoro-2,6-dinitro-ll,ll-dipropyl-p-toluidine) was demethylated (Figure 7) (26), and its atmospheric half-life was found to be 8 minutes (27). However, the reaction occurred to a small extent even at night, and oxidation by ozone was implicated. In fact, there is evidence (28) that parathion photooxidation actually required the presence of ozone or other highly reactive oxidants. Degradation not requiring external reagents also may proceed rapidly trifluralin was cyclized to a substituted benzimidazole (11, 26), and dieldrin again formed photodieldrin (29). 

A library of 2-(arylamino)benzimidazoles was prepared in a microwave-accelerated cyclocondensation of PEG-supported orffto-phcnylenediamines 31 with isothiocyanates, followed by the product cleavage from polymer support [55,56]. The quantitative cyclization required either microwave heating (in an open vessel system) for 10 min or reflux in MeOH for 4 hours (Scheme 20). The use of a soluble PEG matrix substantially simplified the... 

Zhang and Tempest optimized the Ugi/de-Boc/cyclization synthesis for quinoxahnones 27 and benzimidazoles 28 developed by Humles (Scheme 19) [47]. The original thermal reactions required 36-48 h for the Ugi reaction and the condensed products were purified by double scavenging with an immo-... 

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