The enantiomers of 2,2'-dihydroxy-I ,l'-binaphthyl 1 are important C, symmetrical, chiral compounds, whose use is not only limited to asymmetric syntheses."] They are also used for the separation of racemates by the formation of inclusion complexes ['] and as chiral shift reagents.13] The enantiomers of 10,1O-dihydroxy-9,9-biphenanthryl3 are also important chiral host compounds.f41Several methods for the separation of the enantiomers of 1[5.6] and 3L6] have been reported. One of the most effective of these methods is the formation of inclusion complexes with optically active (R,R)-( +)-2,3-dimethoxy-N,N,N',N'-tetramethylsuccinamide (4) and (R,R)-( + )-N,N,N',N'-tetramethyl-2,2-dimethyl-3,3-dioxolane-rrans-4,5-dicarboxamide (5), respectively.[6] One disadvantage of this method, however, is that the amide host compounds (4 and 5)"l are not commerically available, and must be synthesized from tartaric acid prior to the resolution experiment.Recently we have found that commercially available Nalkylcinchonidinium halides (6) are very effective for the resolution of I, the 6,6'-dibromo derivative 2, and the biphenanthryldiol 3 by the formation of inclusion complexes. For example, when a solution of N-benzylcinchonidinium chloride (6a)IS1 (0.74 g, 1.76 mmol) and rac-1 (1 g, 3.5 mmol) in MeOH (20 mL) was kept at room temperature for 6 h, a 1 : 1 inclusion complex of 6a and (+)-1 was obtained, which precipitated as colorless prisms (0.89 g, 72% yield, m.p. 240-244 "C). The 1 : 1 complex was decomposed with dilute HCl. Subsequent extraction with AcOEt, followed by evaporation of the solvent gave (+)-1 (95% ee; 0.35 g, 70% yield, separation of the complex of 6a and (+)-1 was treated with dilute HC1 to give (-)-1 (42% ee; 0.62 g, 124% yield, [a],, = -13.9 (c = 1 .O, THF)). This method is also effective for the separation of the enantiomers of 2. In this case when a solution of 6 a (0.95 g, 2.26 mmol) and rac-2f91 (2 g, 4.5 mmol) in MeOH (2 mL)/AcOEt (10 mL) was kept at room temperature for 6 h, a 1 : 1 inclusion complex of 6a and (-)-2 was obtained, which precipitated in the form of colorless prisms (1.7 g, 89% yield, m.p. 229-232 "C). Decomposition of the complex with dilute HC1 gave (-)-2 (99% ee; 0.82 g, 82% yield, [a],, = -51.0 (c = 0.9, THF)). From the filtrate left after the separation of the inclusion complex, (+)-2 (79% ee; 1.1 g, 110% yield, [a], = +40.7 (c =1.0, THF)) was isolated by treatment with dilute HCI. The enantiomeric purities of 1 and 2 were determined by HPLC by using a column containing an optically active solid phase, Chiralpak AS,"'] and hexane/EtOH (95 : 5) as an eluent.Interestingly, however, 6a was not suitable for the separa-CONMe,
4tion of the e-nantiomers of 3, because 6a does not fork an inclusion complex with 3. In contrast this separation was achieved by the use of N-butylcinchonidinium bromide (6b).["] For example, when a solution of 6b (0.14 g, 0.33 mmol) and rac-3 (0.25 g, 0.65 mmol) in MeCN (10 mL) was kept at room temperature for 24 h, a 1 : 1 inclusion complex of 6 b and (+)-3 was obta...
