Synthesis of substituted chiral chromans via organocatalytic kinetic resolution of racemic 3-nitro-2-aryl-2H-chromenes with ketones catalyzed by pyrrolidinyl-camphor-derived organocatalysts
作者:Dhananjay R. Magar、Kwunmin Chen
DOI:10.1016/j.tet.2012.05.019
日期:2012.7
pyrrolidinyl-camphor derivative 2b as a bifunctionalorganocatalyst under neat conditions in the presence of AcOH at 0 °C. In general, the organocatalyticasymmetricMichaeladdition of ketones proceeded smoothly to give the functionalized Michael adducts (3a–n) with good-to-high diastereo- and enantioselectivities (up to 92:8 dr, 93% ee, and 47% yield). The less reactive chromenes (S)-1a–h, k, l and (R)-1i–j were
An enantioselective oxa-Michael–Henry reaction of substituted salicylaldehydes with nitroolefins that proceeds though an aromatic iminium activation (AIA) has been developed by using a chiral secondary amine organocatalyst and salicylic acid as a co-catalyst. The corresponding 3-nitro-2H-chromenes were obtained in moderate-to-good yields with up to 91% ee under mild conditions. Based on the experimental
The asymmetric domino oxa-Michael–Henry reaction of salicylaldehyde derivatives with trans-β-nitro olefins catalyzed by a readily available trans-4-hydroxy-L-prolinamide with 4-nitrophenol as an effective cocatalyst is presented. The corresponding 3-nitro-2H-chromenes were obtained in moderate to excellent yields (up to 99 %) and with up to 90 % ee under mild conditions. In addition, a preliminary