A Practical Indium Tribromide Catalysed Addition of Indoles to Nitroalkenes in Aqueous Media

Abstract

The 1,4-conjugate addition of indoles to nitroalkenes was efficiently carried out in aqueous media using a catalytic amount of indium tribromide (5 mol%). The reusability of the indium tribromide was tested by performing consecutive cycles with the same catalyst.

Key words

alkaloids - catalysis - indium - indoles - Michael additions

References

• 1a For recent reviews see: Leonard J. Contemp. Org. Synth.  1994,  1:  387 
• 1b Rossiter BE. Swingle NM. Chem. Rev.  1992,  92:  771 
• 2 Fînaru A. Berthault A. Besson T. Guillaumet G. Berteina-Raboin S. Tetrahedron Lett.  2002,  43:  787 
• 3a Zhu HJ. Zhao BT. Zuo GY. Pittman CU. Dai WM. Hao XJ. Tetrahedron: Asymmetry  2001,  12:  2613 
• 3b Paulvannan K. Hale R. Mesis R. Chen T. Tetrahedron Lett.  2002,  43:  203 
• 4a Yevich JP. Yocca FD. Curr. Med. Chem.  1997,  4:  295 
• 4b Jand KS. Barrett V. Brockwell M. Cambridge D. Farrant DR. Foster C. Giles H. Glen RC. Hill AP. Hobbs H. Honey A. Martin GR. Salmon J. Smith D. Woollard P. Selwood DL. J. Med. Chem.  2001,  44:  681 
• 5a Noland WE. Hartman PJ. J. Chem. Soc.  1954,  76:  3227 
• 5b Noland WE. Christensen GM. Sauer GL. Dutton GGS. J. Chem. Soc.  1955,  77:  456 
• 6a Chakrabarty M. Basak R. Ghosh N. Tetrahedron Lett.  2001,  41:  3913 
• 6b Komoto I. Kobayashi S. Org. Lett.  2002,  4:  in press 
• 7 Bandini M. Cozzi PG. Giacomini M. Melchiorre P. Selva S. Umani-Ronchi A. J. Org. Chem.  2002,  67: in press
• 8 Recently, Yadav et. al. reported that InCl₃ (10 mol%) was also able to promote the conjugate addition of indole 5b to 6a in 78% yield using CH₂Cl₂ as the solvent. However, only one example of conjugate addition to nitroalkenes was described, see: Yadav JS. Abraham S. Reddy BVS. Sabitha G. Synthesis  2001,  2165.  Under our conditions, InCl₃ was found less effective in comparison to InBr₃ in the addition of 5a to 6a, 82% yield

9

Other common Lewis acids were found to be less effective in term of chemical yields and reaction times (i.e. AlCl₃, 68% yield, 24 h).