Enantioselective Michael reaction of 2-nitropropane with substituted chalcones catalysed by chiral azacrown ethers derived from α-D-glucose

The chiral monoaza-15-crown-5 lariat ethers anellated to methyl-4,6-O-benzylidene-alpha-D-glucopyranoside 1a-c showed significant asymmetric induction as phase transfer catalysts in the Michael addition of 2-nitropropane to substituted chalcones. Among the catalysts bearing different side arms at the nitrogen atom, the compound with a phosphinoxidoalkyl side chain 1c proved to be the most effective (max. 78% e.e.). The type of substituent on the chalcone was found to have a very significant influence on both the chemical yield and the enantioselectivity of the reaction. The absolute configuration of the Michael adducts 3b and 3i was determined by chemical methods, while that of 3d was assigned by X-ray crystal structure determination. (C) 2002 Elsevier Science Ltd. All rights reserved.