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Synfacts 2009(5): 0565-0565  
DOI: 10.1055/s-0029-1216577
Organo- and Biocatalysis
© Georg Thieme Verlag Stuttgart ˙ New York

Efficient Friedel-Crafts Alkylation of 4,7-Dihydroindoles with Nitroolefins

Contributor(s): Benjamin List, Saihu Liao
Y.-F. Sheng, G.-Q. Li, Q. Kang, A.-J. Zhang, S.-L. You*
Shanghai Institute of Organic Chemistry and Wenzhou University, P. R. of China
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Publication History

Publication Date:
22 April 2009 (online)

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Significance

In this paper a highly efficient enantioselective Friedel-Crafts reaction of 4,7-dihydro-indoles with nitroolefins catalyzed by the chiral phosphoric acid (S)-PA was reported. By slowly adding nitroolefins with a syringe pump, the Friedel-Crafts alkylation of 4,7-dihydroindoles with nitroolefins proceeded effectively with 0.5 mol% of (S)-PA, providing the corresponding alkylation products in high yields (93-98%) and excellent enantioselectivities (er up to 98.5:1.5). After a subsequent oxidation step with 4-benzoquinone, the alkylation products can be converted into 2-substituted indoles, which can be further transformed to enantioenriched tetrahydro-γ-carbolines without erosion of enantiomeric ­excesses.