Chiral Recognition Properties in Complexation of Two Asymmetric Hemicarcerands1

Abstract

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)3PO, 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 °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 Rf 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 °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.