Chiral recognition properties in complexation of two asymmetric hemicarcerands

The synthesis, characterizations and binding properties of new chiral hemicarcerands (S)-1 and (SS)-2 are described. From diol 5 and enantiomerically pure (S)-(-)-3 in Me₂NCOMe-Cs₂CO₃, (S)-1→CHCl₃ was obtained (79%, guest exchanged during isolation). Treatment of 5 with (SS)-4 in Me₂NCOMe-Cs₂CO₃ produced (SS)-2→Me₂-NCOMe (58%). When the chiral bridge of 1 was introduced into 5 in (Me₂N)₃PO, a solvent too large to enter 5 but which contained large excesses of PhC*HOHMe, PhS*OMe or MeCH₂*HMeCH₂OH, the respective diastereomeric ratios of 1→guest produced were 1:1.5, 1:1.5, and 1:1. When (S)-1→CHCl₃ was heated (115-160°C) in the presence of eight different racemic potential guests (neat or in Ph₂O), the CHCl₃ was replaced as guest to give diastereomeric equilibrated ratios for 1→guest that ranged from a high of 2.7:1 for BrCH₂CH₂C*HBrMe to a low of 1:1 for ClCH₂C*HClCH₃ and Me₂CHCH₂CH₂C*HOHMe. The guests that replace CHCl₃ are entering and departing through the chiral portals, which are larger than those which are non-chiral. The diastereomers of 1→PhS*OMe gave widely differing R(f) values (0.41 and 0.27) on thin layer chromatographic plates. Similar introductions of six enantiomeric pair of guests into the innerphase of 2 gave diastereomeric ratios that ranged between 1.4:1 for 2→MeC*HOHCH₂-Me to 1:1 for 2→PhS*OMe, 2→1,2-propranediol, and 2→2-methyl-1-butanol. The two nonchiral 26-membered ring portals are less encumbering than the two chiral 26-membered ring portals of 2. When a mixture of (S)-1 and Ph₂O was heated (25°C, 1 d) with racemic 4-MeC₆H₄S(O)Me, only (S)-1→(R)-4-MeC₆H₄S(O)Me was isolated. When (S)-4-MeC₆H₄S(O)Me was substituted for the racemic sulfoxide, no sulfoxide complex was isolated. The ¹H NMR spectra of the guests in diastereomerically related complexes are substantially different from one another.