Novel efficient bifunctional calixarene thiourea organocatalysts: synthesis and application in the direct enantioselective aldol reactions

Novel efficient bifunctional calixarene thiourea organocatalysts have been designed as efficient organocatalysts for direct asymmetric aldol reactions between acetone and aromatic aldehydes. The reactions generated the corresponding products in satisfactory isolated yields (up to 96%) and with excellent enantiomeric excesses (up to 99%) in the presence of catalyst (10 mol %).

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25,27-Bis(3-((1R,2R)-2-diethylaminocyclohexyl)thiourea)-26,28 dihydroxy-5,11,17,23-tetra(tert-butyl)-calix[4]areneC72H110N6O4S2[α]D20 = +10.6 (c 1, CHCl3)Source of chirality: trans-1,2-diaminocyclohexaneAbsolute configuration: (R,R)

25,27-Bis(3-((1S,2S)-2-dibenzylaminocyclohexyl)thiourea)-26,28-dihydroxy-5,11,17,23-tetra(tert-butyl)-calix[4]areneC92H118N6O4S2[α]D20 = +17.4 (c 1, CHCl3)Source of chirality: trans-1,2-diaminocyclohexaneAbsolute configuration: (S,S)

1-(3-(4-tert-Butylphenoxy)ethyl)-3-((1S,2S)-2(diethylamino)cyclohexyl)thioureaC24H41N3OS[α]D20 = −5.1 (c 1, CHCl3)Source of chirality: trans-1,2-diaminocyclohexaneAbsolute configuration: (S,S)