Synfacts 2011(8): 0832-0832  
DOI: 10.1055/s-0030-1260858
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart ˙ New York

Pd-Catalyzed Synthesis of Indoles via NH3 Cross-Coupling-Alkyne Cyclization

Contributor(s): Victor Snieckus, Timothy Hurst
P. G. Alsabeh, R. J. Lundgren, L. E. Longobardi, M. Stradiotto*
Dalhousie University, Halifax, Canada
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Publikationsverlauf

Publikationsdatum:
20. Juli 2011 (online)

Significance

Reported is the first use of ammonia in the palladium-catalyzed synthesis of 2-aryl indoles 2 from ortho-bromophenylacetylenes 1. Methylamine was also employed to generate N-methyl indoles directly. A variety of functional groups on the R² arene ring are tolerated, including EDGs, halogens and heterocycles, although EWGs (CF3, F) lead to poor yields of products of 2. Only a cursory investigation of substituent effects (R¹) on the aryl bromide was carried out. Interestingly, 1,6-dibromo substitution in 1 led to mono-coupled product 2 (R¹ = 4-Br-6-Me), a valuable precursor for further manipulation by cross-coupling methods. In a significant extension to the methodology, hydrazine was also used to generate N-aminoindoles 3 in moderate yields (along with varying amounts of indazoles 4).