Synthesis of Azapyrrolo[3,2,1-jk]carbazoles, Azaindolo[3,2,1-jk]carbazoles, and Carbazole-1-carbonitriles by Gas-Phase Cyclization of Aryl Radicals

Abstract

Flash vacuum pyrolysis of N-(2-nitroheteroaryl)indoles or -carbazoles at 875 ˚C gave aza analogues of strained pyrrolo[3,2,1-jk]carbazole (50-55%) and indolo[3,2,1-jk]carbazole (55-85%) ring systems, respectively, through generation of aryl radicals and cyclization. The corresponding reactions of N-(2-nitroheteroaryl)indazoles and -benzimidazoles at 850 ˚C, on the other hand, gave carbazole-1-carbonitrile derivatives (56-64%) by a mechanism involving radical ring opening and hydrogen atom rearrangement.

Key words

gas-phase reactions - cyclizations - heterocycles - pyro­lysis - nitro compounds

References

• 1 Crawford LA. McNab H. Mount AR. Wharton SI. J. Org. Chem.  2008,  73:  6642 
• 2 Wharton SI. Henry JB. McNab H. Mount AR. Chem. Eur. J.  2009,  15:  5482 
• 3 Palmer BD. Smaill JB. Boyd M. Boschelli DH. Doherty AM. Hamby JM. Khatana SS. Kramer JB. Kraker AJ. Panek RL. Lu GH. Dahring TK. Winters RT. Showalter HDH. Denny WA. J. Med. Chem.  1998,  41:  5457 
• 4 For a review, see: Wolfe JP. Wagaw S. Marcoux JF. Buchwald SL. Acc. Chem. Res.  1998,  31:  805 
• 5 Rüchardt C. Meier M. Haaf K. Pakusch J. Wolber EKA. Müller B. Angew. Chem. Int. Ed. Engl.  1991,  30:  893 
• 6 For example, see: Cadogan JIG. Hutchison HS. McNab H. Tetrahedron  1992,  48:  7747 
• 7 Suzuki T. Kinoshita A. Kawada H. Nakada M. Synlett  2003,  570 
• 8 For example, see: Guertler CF. Blechert S. Steckhan E. Synlett  1994,  141 
• 9 Adachi M. Sugasawa T. Synth. Commun.  1990,  20:  71 
• 10 Khan MA. Polya JB. J. Chem. Soc. C  1970,  85 
• 11 Tsuge O. Samura H. J. Heterocycl. Chem.  1971,  8:  707 
• 12 McNab H. Aldrichimica Acta  2004,  37:  19 
• 13 Kusurkar RS. Pati UG. Indian J. Chem., Sect. B: Org. Chem. Incl. Med. Chem.  1986,  25:  1038