Benzimidazole, 2-phenyl-, from

Cycloaddition and cyclization routes were used to access certain 1,3-diazines. The 4+2 cycloaddition reaction of 4-(N-allyl-N-aryl)amino-l,3-diaza-l,3-butadienes with vinyl-, isopropenyl-, and chloroketene led to pyrimidinone-fused pyrimidinones <97T13841>. Cis-cyclopenta[d]pyrimidines were derived from cis-2-amino-l-cyclopentanecarboxylates by cyclization with KOCN and KSCN <97JHC1211>. 2-Thioxopyrido[3, 2 4,5]thieno[3,2-r/]pyrimidin-4(3//)-ones 19 were prepared by cyclocondensation of 2-carbethoxy-3-amino-4-phenyl-6-substituted-thieno[2,3-/)]pyridines and isothiocyanates <97JHC937>. Thiazolyl-benzimidazoles derived from 2-cyanomethyl-l//-benzimidazole and 2,3-dihydrothiazole-2-(3//)-thiones were cyclized to the corresponding thiazolo[4,5-r/]pyrimidines <97PHA346>. Reductive cyclization of 6-cyanomethyl-5-nitropyrimidines afforded 7-alkyl-5//-pyrrolo[3,2-r/]pyrimidines and 6-amino-7,7-dialkyl-7//-pyrrolo[3,2-rf]pyrimidines <97T391>. 7-Methyl-5-alkyl-2-vinyl-pyrazolo[3,4-r/]pyrimidine-4,6(5//,7//)-diones arose from cyclization and alkylation of... 

The solubility of IL is strictly dependent on melting temperature of the solute, which is generally the result of the alkane or phenyl substituents at imidazolium ring. The conclusions can be taken from the solubilihes of benzimidazole and 2-phenylimidazole in water [94] and of every measured imidazoles in organic solvents [83-89]. 

Poly(arylene ether benzimidazole)s have received more attention than any other PAE containing heterocyclic units. This is due primarily to their unique combination of properties even at relatively low molecular weights and their potential for use in several high performance applications. The initial report in 1991 involved polymers from the reaction of 3 different bis[(4-hydroxy-phenyl)benzimidazole]s with various activated aromatic difluoro monomers as shown in Eq. (10) [37]. The bis[(4-hydroxyphenyl)benzimidazole]s were prepared from the reaction of aromatic bis(o-diamines) and phenyl-4-hydroxybenzoate in diphenyl sulfone. The use of 4-hydroxybenzoic acid would obviously reduce the... 

Substituted imidazoles can be acylated at the 2-position by acid chlorides in the presence of triethylamine. This reaction proceeds by proton loss from the TV-acylated intermediate (311). An analogous reaction with phenyl isocyanate gives (312), probably via a similar mechanism. Benzimidazoles react similarly (87CHE284), but most pyrazoles do not (80AHC(27)24i) (cf. Section 3.4.1.4.6). 

Improved yields are obtained from p-tolyl-substituted imidazoles and benzimidazoles provided that the 1-nitrogen atom is substituted. l-(p-Tolyl)-2,4,5-triphenylimidazole (130) gives, with benzalaniline, l-(stilben-4-yl)-2,4,5-triphenylimidazole (131), and l-phenyl-2-(p-tolyl)-benzimidazole (132) the stibenyl derivative 133.11... 

In going from benzene to 3-carotene (the second structure), the Y value increases by more than three orders of magnitude showing the importance of increase in the effective conjugation length. The third structure exhibits N-phenyl substitution in the benzimidazole type structures to introduce a two dimensional conjugation. The last structure, an organometallic polymer, has also been measured in the solution phase. Because of the resonance condition encountered, the Y value is.complex. 

Hexakis(benzimidazol-r-yl)benzene (14) [29], due to the loss of symmetry on going from the phenyl to the lH-benzimidazolyl ring, can exist in eight conformations (Fig. la-h), depending on whether the N(3) atom is up (black circle) or down (white circle). A mixture of three conformers were isolated and identified (Fig. lc, e and f). 

A particular case of a photochemical strategy towards functionalized benzimidazoles regards the synthesis of 2-acylamino derivatives 70, which can be obtained from irradiations in methanol of 3-(o-amino)phenyl-l,2,4-oxadiazoles 68. In this reaction, a photolytic cleavage of the ring O—N bond, followed by migration of the aryl substituent, leads to the carbodiimide intermediate 69, a precursor of the benzimidazole nucleus (Scheme 12.20) [47]. 

A word of caution at this point seems most desirable. In every case where a pure aldonic acid or its derivative has been heated with o-phenyl-enediamine and an excess of hydrochloric acid, only a single benzimidazole has been isolated. It is well known that aldonic acids are epimerized by heating them at temperatures above 100° with organic bases such as pyridine. The heating of an aldonic acid with o-phenylenediamine at 135-150° may also result in appreciable epimerization. Thus, Moore and Link20 reported that from the fusion of xylonic acid with o-phenylenediamine at 150°, in the absence of mineral acids, they could isolate the epimeric lyxo-benzimidazole. Barker, Farrar, and Gulland,21 in a more detailed study, proved conclusively that both D-ribo- and D-arabo-benzimidazoles were formed when the condensation of calcium D-ribonate with o-phenylenediamine was carried out in the presence of less than two molecular equivalents of hydrochloric acid, whereas with an excess of hydrochloric acid only the D-ribo-benzimidazole was obtained. It is important, therefore, in the condensation of o-phenylenediamine with an optically active acid at an elevated temperature that the reaction mixture always be kept on the acid side. 

In the formation of a benzimidazole the steps involving loss of a methyl ketone, which are essentially irreversible, control the course of the reaction. Examples of such ring-contraction reactions are the formation of 2-methyl-benzimidazole and acetone from 2,4-dimethylbenzodiazepine and its salts (07CB955 59JCS1132 65JCS3785) and of a mixture of acetone, acetophenone, 2-methyl-, and 2-phenyl-benzimidazoles from 2-methyl-4-phenyl-benzodiazepine (07CB955). The same ring contractions also ensue when aqueous solutions of benzodiazepines or their salts are kept at room temperature. It seems likely that in the case of solutions of the salts, some free base, present in equilibrium with the cation, may be the species in-... 

On pyrolysis, 1-arylimidazoles rearrange to 2-arylimidazoles. In other systems, pyrolysis causes more deep-seated changes. 1-Arylbenzotriazoles on pyrolysis or photolysis give carbazoles via intermediate nitrenes (see Section 3.4.1.2.1). 1-Phenyl-1,2,4-triazole 789 is converted by pyrolysis into isoindole 790 via a carbene intermediate and another example of the participation of A-phenyl groups is found in the formation of benzimidazoles from tetrazoles (see Section 3.4.1.2.1). In the oxadiazolinone series, a nitrene intermediate 791 is also probably formed, which then ring closes. 

N-Aryl substituents usually depress the basic properties of the imidazole or benzimidazole nucleus. The effects of substituents on the aryl group are evident from the data listed in Table 7 which also lists rate constants for quaternization with iodoethane, a reaction which is dependent upon the nucleophilic character of the pyridine-type nitrogen (70CHE194). A phenyl group withdraws electrons from the imidazole ring, but does so rather weakly. The p value of +0.753 for the protonation process is in accord with weak electron transfer from the phenyl substituent to the basic nitrogen. 

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