C([C:5]1[CH:12]=[C:11](C(C)(C)C)[CH:10]=[C:7]([CH:8]=O)[C:6]=1[OH:17])(C)(C)C.[C:18]([C:22]1[CH:27]=[C:26](C(C)(C)C)[CH:25]=[CH:24][C:23]=1[OH:32])(C)(C)C.[NH2:33][C@H:34]1CCCC[C@@H:35]1[NH2:40].O>C(O)C>[CH:11]1[CH:12]=[CH:5][C:6](=[O:17])/[C:7](=[CH:8]\[NH:33][CH2:34][CH2:35][NH:40]/[CH:18]=[C:22]2\[C:23]([CH:24]=[CH:25][CH:26]=[CH:27]\2)=[O:32])/[CH:10]=13,5-Di-t-butylsalicylaldehyde (2.0 equivalents) (prepared from the inexpensive, commercially available 2,4-di-t-butylphenol according to Larrow, J. F.; Jacobsen, E. N.; Gao, Y.; Hong, Y.; Nie, X.; Zepp, C. M. J. Org Chem 1994, 59, 1939) was added as a solid to a 0.2 M solution of (S,S)-1,2-diaminocyclohexane (1.0 equivalent) (Aldrich Chemical Co., Milwaukee, Wis.) in absolute ethanol. The mixture was heated to reflux for 1 hr. and then H2O was added dropwise to the cooled bright yellow solution. The resulting yellow crystalline solid was collected by filtration and washed with a small portion of 95% ethanol. The yield of analytically pure salen ligand obtained in this manner was 90-97%.
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