A New Method for the Synthesis of 2-Aryl-1H-benzimidazoles: Selenium-­Catalyzed Reductive N-Heterocyclization of Benzylidene(2-nitroaryl)amines with Carbon Monoxide

Abstract

The treatment of benzylidene(2-nitroaryl)amines, prepared by the reaction of o-nitro aniline and benzaldehydes, with carbon monoxide in the presence of a catalytic amount of selenium under basic conditions, afforded 2-aryl-1H-benzimidazoles in ­moderate to good yields.

Key words

selenium - carbon monoxide - 2-aryl-1H-benzimidazole - benzylidene(2-nitroaryl)amine

References and Notes

• 1 For recent reviews; see: Grimmett MR. Imidazoles and their Benzo Derivatives, In Comprehensive Heterocyclic Chemistry   Vol. 5:  Katritzky AR. Rees CW. Pergamon Press; Oxford: 1984.  p.457-498  
• 2a Tolari S. Cenini S. Crotti C. Gianelloy E. J. Mol. Catal.  1994,  87:  203 
• 2b Crotti C. Cenini S. Ragaini F. Porta F. Tolari S. J. Mol. Catal.  1992,  72:  283 
• 2c Watanabe Y. Suzuki N. Tsuji Y. Bull. Chem. Soc. Jpn.  1982,  55:  2445 
• 2d Watanabe Y. Takatsuki K. Shim SC. Mitsudo T. Takegami Y. Bull. Chem. Soc. Jpn.  1978,  51:  3397 
• 3 It has already been reported that the reaction of benzyl-idene(2-nitrophenyl)amine with triethyl phosphite affords 2-phenyl-1H-benzimidazole in 47% yield. See: Cadogan JIG. Marshall R. Smith DM. Todd MJ. J. Chem. Soc. C.  1970,  2441 
• 5 Nishiyama Y. Maema R. Ohno K. Hirose H. Sonoda N. Tetrahedron Lett.  1999,  40:  5717 
• 6 Nishiyama Y. Hirose H. Kitagaito W. Sonoda N. Tetrahedron Lett.  2002,  43:  1855 
• 7 Nishiyama Y. Naitoh Y. Sonoda N. Synlett  2004,  886 
• 9 Kondo K. Yokoyama S. Miyoshi N. Murai S. Sonoda N. Angew. Chem., Int. Ed. Engl.  1979,  18:  691 
• 10 For the transition-metal-catalyzed N-heterocyclization, it was suggested that the generation of the nitrene (or nitrenoid) intermediate was the key step in the reaction. For a review, see: Soderberg BCG. Curr. Org. Chem.  2000,  4:  727 

4

We have recently reported the selenium-catalyzed reductive N-heterocyclization of 2-nitrostyrenes, [5] N-(2-nitro-benzoyl)amides, [6] or 2-nitrobenzyl alcohols [7] with carbon monoxide that produced indoles, 3,4-dihydroquinazolin-4-ones, or 1,4-dihydro-2H-3,1-benzoxazin-2-ones.

8

A typical procedure is as follows: in a 50 mL stainless steel autoclave were placed benzylidene(2-nitroaryl)amine (0.5 mmol), selenium (8 mg, 0.1 mmol), DBU (304 mg, 2 mmol), 1,4-dioxane (5 mL), MS 3 Å (0.3 g) and a magnetic stirring bar. The mixture was stirred under pressurized carbon monoxide (30 atm) at 120 °C for 3 h. After evacuation of the excess carbon monoxide at r.t., the deposited selenium and MS 3 Å were filtered off. DBU was removed by reduced distillation. The residual solution was purified by chromatography on neutral aluminum oxide (CHCl₃ as eluent) to give the 2-aryl-1H-benzimidazoles.