In Situ Generation and Synthetic Application of 2-Phenylbenzimidazoline to the Selective Reduction of Carbon–Carbon Double Bonds of Electron-Deficient Olefins

Abstract

2-Phenylbenzimidazoline (PBI) as a mild, selective, and convenient reducing agent was efficiently generated in situ from o-phenylenediamine and benzaldehyde in alcohols. A generally applicable method for the selective reduction of carbon–carbon double bonds of a variety of electron-deficient olefins with an alcoholic solution of PBI is described. The reduction of α,β-unsaturated ketones to the corresponding saturated ketones could also be accomplished (but, less effectively) with PBI with the aid of a Lewis-acid catalyst. 1-Methyl-2-(o-nitrophenyl)benzimidazoline prepared and isolated by the reaction of o-nitrobenzaldehyde with N-methyl-o-phenylenediamine reduced benzylidenemalononitrile to give benzylmalononitrile and 1-methyl-2-(o-nitrophenyl)benzimidazole in high yields. This shows the validity of PBI to be the actual reducing species in the present reduction system. From a mechanistic study, the present reductions could be interpreted in terms of a mechanism involving a synchronous transport of a pair of hydrogens or a sequential transfer of a hydride and a proton from PBI to the olefins.

Reusable Cobalt(III)‐Salen Complex Supported on Activated Carbon as an Efficient Heterogeneous Catalyst for Synthesis of 2‐Arylbenzimidazole Derivatives

“…[5] Various oxidative reagents such as nitrobenzene (high-boiling point oxidant/solvent), [10] 1,4-benzoquinone, [11] air, [5] InA C H T U N G T R E N N U N G (OTf) 3 , [1b] PhIA C H T U N G T R E N N U N G (OAc) 2 , [12] Zn-proline, [13] heteropoly acids, [14] thionyl chloride-treatment, [15] DDQ, [16] electron-deficient olefins, [17] benzofuroxan, [18] MnO 2 , [19] PbA C H T U N G T R E N N U N G (OAc) 4 , [20] oxone, [21] NaHSO 3 , [22] H 2 O 2 /HCl [23] and Na 2 S 2 O 5 [24] have been employed. Because of the availability of a vast number of aldehydes, the condensation of phenylenediamines with aldehydes has been extensively used.…”

An Inorganic Iodine‐Catalyzed Oxidative System for the Synthesis of Benzimidazoles Using Hydrogen Peroxide under Ambient Conditions

“…Various oxidative reagents, such as MnO 2 , [15] Pb(OAc) 4 , [16] PhI(OAc) 2 , [17] Oxone, [18] DDQ, [19] I 2 , [20] 1,4-benzo-quinone, [21] tetracyanoethylene, [22] benzofuroxan, [23] NaHSO 3 , [24] Na 2 S 2 O 5 , [25] (NH 4 ) 2 S 2 O 8 , [26] and nitrobenzene or DMF (high-boiling oxidant/solvent) [27] have been employed to effect the dehydrogenation step. Although many of these methods are practical, some have problems such as the use of dangerous or toxic reagents, or the formation of N-benzylbenzimidazole side products resulting from further reaction of the aldehyde with benzimidazoline prior to oxidation.…”

Highly Efficient and Facile Method for Synthesis of 2-Substituted Benzimidazoles via Reductive Cyclization of O-Nitroaniline and Aryl Aldehydes

“…The other way involves a two-step procedure that is oxidative cyclodehydrogenation of aniline schiff 's bases, which are often generated in situ from the condensation of o-phenylenediamines and aldehydes. Various oxidative reagents such as tetracyano ethylene [5], nitrobenzene [6], 1,4-benzoquinone [7], DDQ [8], benzofuroxan [9], NaHSO 3 [10], MnO 2 [11], oxone [12], DMP [13], Pb(OAc) 4 [14], and NH 4 VO 3 [15] have been employed. However, all of these methods have problems, including drastic reaction conditions, expensive catalyst, low yields, and severe side-reactions.…”