Synthesis of new calix[4]arene based chiral ligands bearing β-amino alcohol groups and their application in asymmetric transfer hydrogenation

A new series of chiral calix[4]arenes bearing β-amino alcohol groups have been synthesised. The crucial steps consist of the binding of glycidyl groups on the lower rim of the calix[4]arenas, followed by their regioselective opening with amines. These ligands were successfully tested in an asymmetric transfer hydrogenation. The best results (conversion max = 97% and ee max = 87%) were obtained using calix[4]arene mono-functionalised ligands. These results are the best ones obtained using calixarene based ligands in asymmetric catalysis.

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5,11,17,23-Tetra-tert-butyl-25,27-tris-(propoxy)-26,28-bis[((2R)-3-benzylamino-2-hydroxy)propoxy]calix[4]areneC70H94N2O6Ee = 99%[α]D25=+3.4 (c 0.75, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(R,R)

25,27-Dipropoxy-26,28-bis[((2R)-3-benzylamino-2-hydroxy)propoxy]calix[4]areneC54H82N2O6Ee = 99%[α]D25=-36.3 (c 0.885, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(R,R)

(2R)-1-(Trityloxymethyl)-3-cyclohexanemethylaminopropan-2-olC29H35NO2Ee = 99%[α]D25=+10.6 (c 1, CHCl3)Source of chirality:asymmetric synthesisAbsolute configuration:(R)

(R)-5,11,17,23-Tetra-tert-butyl-25,26,27-tris-(propoxy)-28-glycidylcalix[4]areneC56H78O6Ee = 99%[α]D25=-2.2 (c 1.135, CHCl)Source of chirality:asymmetric synthesisAbsolute configuration:(R)

(R,R)-5,11,17,23-Tetra-tert-butyl-25,27-dipropoxy-26,28-bis(glycidyl)calix[4]areneC58H76O6Ee = 99%[α]D25=-6.2 (c 0.975, CHCl)Source of chirality:asymmetric synthesisAbsolute configuration:(R,R)

(R,R)-25,27-Dipropoxy-26,28-bisglycidylcalix[4]areneC40H44O8Ee = 99%[α]D25=-8.5 (c 1.015, CHCl)Source of chirality: asymmetric synthesisAbsolute configuration: (R,R)

5,11,17,23-Tetra-tert-butyl-25,26,27-tris-(propoxy)-28-[((2R)-3-benzylamino-2-hydroxy)propoxy]calix[4]areneC6H87NO5Ee = 99%[α]D25=-2.5 (c 0.91, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (R)