Synthesis of calix[4]arene derivatives bearing chiral pendant groups as ligands for enantioselective catalysis

New chiral calix[4]arene derivatives have been synthesized by appending at the lower rim amino acid (l-tyrosine, l-aspartic acid, l-valine, and l-tryptophan) or pinene-like (myrtenyl and homomyrtenyl) units or by distal intrabridging with a binaphthyl amine scaffold. The application of these derivatives in enantioselective catalysis was studied by testing the catalytic activities of the corresponding Ti(IV)/calixarene complexes, prepared in situ, in the asymmetric aldol reaction of Chan’s silyloxydiene with p-nitrobenzaldehyde.

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5,11,17,23-Tetra-tert-butyl-25-[O-methyl-O′-tert-butyl-(S)-tyrosinyl-carbonylmethoxy]calix[4]aren-26,27,28-triolC60H77NO8[α]D25=-36 (c 3.91, CHCl3)Source of chirality: l-tyrosine

5,11,17,23-Tetra-tert-butyl-25-[bis(O-tert-butyl)-(S)-aspartyl-carbonylmethoxy]calix[4]aren-26,27,28-triolC58H79NO9[α]D25=-5.1 (c 0.4, CHCl3)Source of chirality: l-aspartic acid

5,11,17,23-Tetra-tert-butyl-25-[O-methyl-(S)-valinyl-carbonylmethoxy]calix[4]aren-26,27,28-triolC52H69NO7[α]D25=-1.5 (c 0.83, CHCl3)Source of chirality: l-valine

5,11,17,23-Tetra-tert-butyl-25-[O-methyl-(S)-tryptophanyl-carbonylmethoxy]calix[4]aren-26,27,28-triolC58H70N2O7[α]D25=-22 (c 4.1, CHCl3)Source of chirality: l-tryptophan

5,11,17,23-Tetra-tert-butyl-25,27-bis[O-methyl-O′-tert-butyl-(S)-tyrosinyl-carbonylmethoxy]calix[4]aren-26,28-diolC76H98N2O12[α]D25=+22 (c 0.7, CHCl3)Source of chirality: l-tyrosine

5,11,17,23-Tetra-tert-butyl-25,27-bis[(R,R)-6,6-dimethyl-bicyclo[3.1.1]hept-2-ene-2-methoxy]calix[4]aren-26,28-diolC64H84O4[α]D25=+2.6 (c 1.9, CHCl3)Source of chirality: (R,R)-6,6-dimethyl-bicyclo[3.1.1]hept-2-ene-2-methanol [(−)- myrtenol]

5,11,17,23-Tetra-tert-butyl-25,27-bis[(R,R)-6,6-dimethyl-bicyclo[3.1.1]hept-2-ene-2-ethoxy]calix[4]aren-26,28-diolC66H88O4[α]D25=-15 (c 1.5, CHCl3)Source of chirality: (R,R)-6,6-dimethyl-bicyclo[3.1.1]hept-2-ene-2-ethanol [(−)-Nopol]

5,11,17,23-Tetra-tert-butyl-25,27-[(S)-binaphthyl-2,2′-bis(aminocarbonylmethoxy)]calix[4]aren-26,28-diolC68H72N2O6[α]D25=-89 (c 2.5 CHCl3)Source of chirality: (S)-(−)-2,2′-diamino-1,1′-binaphthalene

5,11,17,23-Tetra-tert-butyl-25-[(R,R)-6,6-dimethyl-bicyclo[3.1.1]hept-2-ene-2- methoxy-carbonylmethoxy]calix[4]aren-26,27,28-triolC56H72O6[α]D25=-8.0 (c 2.8, CHCl3)Source of chirality: (R,R)-6,6-dimethyl-bicyclo[3.1.1]hept-2-ene-2-methanol [(−)-myrtenol]