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.Me2NCOMe (58%). When the chiral bridge of 1 was introduced into 5 in (Me2N)(3)PO, a solvent too large to enter 5 but which contained large excesses of PhC*HOHMe, PhS*OMe or MeCH2C*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 degrees 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 pairs of guests into the inner phase of 2 gave diastereomeric ratios that ranged between 1.4:1 for 2.MeC*HOHCH2Me to 1:1 for 2.PhS*OMe, 2.1,2-propanediol, 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 degrees 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 H-1 NMR spectra of the guests in diastereomerically related complexes are substantially different from one another.