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4279659 
Journal Article 
Tris-ureas as versatile and highly efficient organocatalysts for Michael addition reactions of nitro-olefins: Mechanistic insight from in-situ diagnostics 
Bera, M; Ghosh, TK; Akhuli, B; Ghosh, P 
2015 
Yes 
Journal of Molecular Catalysis A: Chemical
ISSN: 1381-1169 
408 
287-295 
English 
WOS:000361254400033 
Tris(2-aminoethyl)-amine, TREN based tris-ureas (1a-1d) and tris-thiourea (1e) have been explored towards a wide range of catalytic Michael addition reactions. These tris-ureas, 1a-1d efficiently catalyze the addition reaction of beta-nitro styrenes (2a-2d) with various nucleophiles such as beta-ketoesters (3a-3c), 1,3-dicarbonyl compound (3d), a cyanoester (3e) and a nitroester (3f) under ambient conditions to produce corresponding nitro alkanes in high yields. Pentafluorophenyl attached tris-urea, 1d is found to be the most effective catalyst in the series that yields 78-98% products conversion. In case of the reaction between beta-nitro styrenes and malononitrile (3g) in presence of 1d, 2-amino-5-nitro-4,6-diphenylcyclohex-1-ene-1,3,3-tricarbonitriles are also isolated as a minor product along with the corresponding Michael adduct. The added advantage of bridge-head nitrogen center in tris-urea organocatalysts, 1a-1d has been established by studying analogous benzene platform based tris-ureas (1f, 1g, 1h) in similar experimental conditions. Furthermore, a plausible reaction mechanism has also been established based on in-situ H-1 NMR kinetic studies. (C) 2015 Elsevier B.V. All rights reserved. 
Michael addition reaction; Tris-urea catalyst; Organocatalysis; Hammett plot