Benzimidazoline reduction

Nickel chloride promoted desulfurization and reductive cleavage of N,N -diarylthioureas gives corresponding anilines and tV-methylanilines (Scheme 69). While 7V,tV -dialkylthioureas undergo desulfurization to give formami-dines, and benzimidazoline-2-thiones underwent desulfurization to benzimidazoles (Scheme 69).159... 

Photolytic. Irradiation of trifluralin in hexane by laboratory light produced a,a,a-trifluoro-2,6-dinitro-A-propyl-jo-toluidine and a,a,a-trifluoro-2,6-dinitro-p-toluidine. The sunlight irradiation of trifluralin in water yielded a,a,a-trifluoro-A, 7 -dipropyl-5-nitrotoluene-3,4-diamine, a,a,a-trifluoro-A/ ,A/ -dipropyltoluene-3,4,5-triamine, 2-ethyl-7-nitro-5-(trifluoromethyl)benzimidazole, 2,3-dihydroxy-2-ethyl-7-nitro-l-propyl-5-(trifluoromethyl)benzimidazoline, and 2-ethyl-7-nitro-5-(trifluoromethyl)benzimidazole. 2-Amino-6-nitro-a,a,a-trifluoro-p-toluidine and 2-ethyl-5-nitro-7-(trifluoromethyl)benzimidazole also were reported as major products under acidic and basic conditions, respectively (Crosby and Leitis, 1973). In a later study, Leitis and Crosby (1974) reported that trifluralin in aqueous solutions was very unstable to sunlight, especially in the presence of methanol. The photodecomposition of trifluralin involved oxidative TV-dealkylation, nitro reduction, and reductive cyclization. The principal photodecomposition products of trifluralin were 2-amino-6-nitro-a,a,a-trifluoro-jo-toluidine, 2-ethyl-7-nitro-5-(trifluoromethyl)benzimida-zole 3-oxide, 2,3-dihydroxy-2-ethyl-7-nitro-l-propyl-5-(trifluoromethyl)benzimidazole, and two azoxybenzenes. Under alkaline conditions, the principal photodecomposition product was 2-ethyl-7-nitro-5-(trifluoromethyl)-benzimidazole (Leitis and Crosby, 1974). 

The exclusive coordination of the C5 carbon atom in complex 48 was achieved by a reduction of the bite angle [147]. Blocking of the C4 and C5 positions as seen in benzimidazolin-2-ylidenes led to the complex with the C2-metalated NHC ligand 49 [147]. No transformation of a C5-coordinated NHC ligand into a C2-coordinated one, i.e., conversion of 46 to 47 or vice versa, has been observed so far. 

Complex 61 is also accessible from the 2-nitrophenyl isocyanide complex 68 by reduction of the nitro group with Sn/HCl. Incomplete reduction of the nitro group in 68 with Raney-Nickel/hydrazine yields, after intramolecular cyclization, the complex 70 with the NH,NOH-stabilized benzimidazolin-2-ylidene ligand. Complex 69 with the 2-hydoxylamin-substituted phenyl isocyanide ligand presumably occurs as an intermediate in this reaction. The alkylation of both the NH,NH- and the NH, NOH-stabilized NHC ligands in 67 and 70, respectively, proceeds readily (Fig. 23) [184, 185]. 

Compound 639 also promotes the photo induced reduction of ketones whereas 2-(2 -hydroxyphenyl)-l,3-dimethyl-benzimidazoline 640 promotes benzpinacol formation (Scheme 153) <2005JOC9632>. Photoinduced single electron transfer (SET) followed by regiospecific proton transfer (PT) led to the formation of either benzhydrol or benzpinacol, depending on the 2-aryl substituent. 

NHCs have become popular ligands in coordination chemistry owing to the facile access to this type of ligands and to metal-NHC complexes. Most NHC ligands are prepared from azohum compounds such as imidazolium, triazolium, benzimidazo-lium, imidazolidinium, or thi azolium salts [1]. Alternatively, the reductive desulfurization of imidazolin-, benzimidazolin-, and imidazolidin-2-thiones to yield a variety of NHCs has been described. The preparation of suitable azolium salts and imidazolin-2-thiones is presented in Sect. 2.1. This is followed by the description of methods to liberate the free NHCs from these compounds. Today, stable singlet... 

Coordination chemistry of organo-hydride donors (dihydropyridines, dihydroacridines, benzimidazolines, benzoxazolines etc.) New prospects for efficient multielectron reduction 13CSR5439. 

Nature makes use of NADH (reduced nicotinamide adenine dinucleotide) as a cofactor for enantioselective biochemical hydrogenations, which are typical hydride-transfer reactions. Dihydropyridines and benzimidazolines derivatives are active hydride donors due to the presence of the nitrogen atom and the ability of the molecule to undergo aromatisation. Organocatalytic enantioselective reductions carried out using hydride donors has been studied, and effective reductions have been achieved with imidazoli-dinone organocatalysts, both with a,p unsaturated aldehydes and ketones. Generally, a stoichiometric quantity of reductant (Hantzsch ester 4) is required for these transformations (Scheme 18.5). 

In 1999, the first annulated carbene derived from benzimidazole, l,3-bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene, was prepared by the reduction of A/,N -dialk ylated benzimidazol-2-thione with Na/K in toluene [44]. Frequently, benzimidazolium ions containing less bulky Af-alkyl groups interconvert rapidly into enetetramine derivatives. Even when the formation of these compounds can be avoided by sterically demanding substituents, the final generation of the carbene may fail. 

Hasegawa E, Takizawa S, Seida T, Yamaguchi A, Yamaguchi N, Chiba N, Takahashi T, Bceda H, Akiyama K (2006) Photoinduced electron-transfer systems consisting of electron-donating pyrenes or anthracenes and benzimidazolines for reductive transformation of carbonyl compounds. Tetrahedron 62 6581-6588... 

Chikashita, H. and Itoh, K., AlClj-promoted conjugate reduction of a,P-unsaturated carbonyl compounds with l,3-dimethyl-2-phenyl-benzimidazoline. Bull. Chem. Soc. Jpn., 59, 1747,1986. Chikashita, H., Ide, H., and Itoh, K., l,3-dimethyl-2-phenyl-benzimidazoline as a novel and efficient reagent for mild reductive dehalogenation of a-halo carbonyl compounds and acid chlorides, J. Org. Chem., 51, 5400,1986. 

Hasegawa, E., Yoneoka, A., Suzuki, K., Kato, T., Kitazume, T, and Yanagi, K., Reductive transformations of ot,P-epoxy ketones and other compounds promoted through photoinduced electron transfer processes with l,3-dimethyl-2-phenyl-benzimidazoline (DMPBl), Tetrahedron, 55,12957, 1999. 

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