Several years ago, while investigating the possibility to use beta-nitrostyrenes as aminating agents for olefins following our protocol originally devised for nitroarenes, we found that a cyclization reaction to give indoles was observed instead. Better results were obtained employing palladium as catalyst in place of ruthenium. The reaction conditions were optimized using beta-methyl-beta-nitrostyrene (1a) as substrate and some results with different substrates are reported below. While our work was in progress, Hsieh and Dong reported a similar approach for the synthesis of 3-arylsubstituted indoles from alpha-aryl-beta-nitrostyrenes (R1= H, R2 = Ar in the scheme above). Experimental conditions reported in that paper are milder (100 °C, DMF, 2 bar CO absolute pressure) then ours. We reproduced those results and we confirm they work well for alpha-aryl-beta-nitrostyrenes, but fail almost completely when R1 is not H, whereas our conditions are suitable also in this case. Unlike most reported cyclization reaction affording indoles, our strategy does not require the use of a doubly functionalized arene (e.g. an o-bromoaniline) and in most cases the starting materials can be easily prepared by a Henry reaction.

Carbon monoxide as a reductant: synthesis of indoles by palladium catalyzed reductive cyclization of beta-nitrostyrenes / M. Elatawy, M. Hagar, F. Ferretti, D. Formenti, S. Muto, F. Ragaini. ((Intervento presentato al 13. convegno Sigma Aldrich Young Chemists Symposium tenutosi a Riccione nel 2013.

Carbon monoxide as a reductant: synthesis of indoles by palladium catalyzed reductive cyclization of beta-nitrostyrenes

M. Elatawy;F. Ferretti;D. Formenti;F. Ragaini
2013-10

Abstract

Several years ago, while investigating the possibility to use beta-nitrostyrenes as aminating agents for olefins following our protocol originally devised for nitroarenes, we found that a cyclization reaction to give indoles was observed instead. Better results were obtained employing palladium as catalyst in place of ruthenium. The reaction conditions were optimized using beta-methyl-beta-nitrostyrene (1a) as substrate and some results with different substrates are reported below. While our work was in progress, Hsieh and Dong reported a similar approach for the synthesis of 3-arylsubstituted indoles from alpha-aryl-beta-nitrostyrenes (R1= H, R2 = Ar in the scheme above). Experimental conditions reported in that paper are milder (100 °C, DMF, 2 bar CO absolute pressure) then ours. We reproduced those results and we confirm they work well for alpha-aryl-beta-nitrostyrenes, but fail almost completely when R1 is not H, whereas our conditions are suitable also in this case. Unlike most reported cyclization reaction affording indoles, our strategy does not require the use of a doubly functionalized arene (e.g. an o-bromoaniline) and in most cases the starting materials can be easily prepared by a Henry reaction.
indole; reductive carbonylation; palladium catalysis
Settore CHIM/03 - Chimica Generale e Inorganica
Società Chimica Italiana
Sigma Aldrich
Carbon monoxide as a reductant: synthesis of indoles by palladium catalyzed reductive cyclization of beta-nitrostyrenes / M. Elatawy, M. Hagar, F. Ferretti, D. Formenti, S. Muto, F. Ragaini. ((Intervento presentato al 13. convegno Sigma Aldrich Young Chemists Symposium tenutosi a Riccione nel 2013.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/249311
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