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Synfacts 2007(7): 0762-0762  
DOI: 10.1055/s-2007-968628
Organo- and Biocatalysis
© Georg Thieme Verlag Stuttgart · New York

Organocatalytic Intramolecular Friedel-Crafts-Type Alkylation of Indoles

Contributor(s): Benjamin List, Subhas Chandra Pan
C.-F. Li, H. Liu, J. Liao, Y.-J. Cao, X.-P. Liu, W.-J. Xiao*
Central China Normal University, Hubei, P. R. of China
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Publication History

Publication Date:
22 June 2007 (online)

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Significance

An organocatalytic asymmetric intramolecular ring-closing Friedel-Crafts-type alkylation of indolyl α,β-unsaturated aldehydes has been described. This method allows the preparation of tetrahydropyrano[3,4-b]indoles and tetra­hydro-β-carbolines in an atom-economical manner. MacMillan’s imidazolidinone catalyst 1 in combination with 3,5-dinitrobenzoic acid has been identified as the best catalyst system for this reaction. With 20 mol% of catalyst 1 moderate to high yields (48-89%) and high enantioselectivities (er = 90:10 to 97:3) are obtained for different indolyl aldehydes. A phenoxyl-substituted α,β-unsaturated aldehyde has also been used and high enantioselectivity (er = 95:5) was attained.