Syntheses, binding properties, and structures of seven new hemicarcerands each composed of two bowls bridged by three tetramethylenedioxy groups and a fourth unique linkage

Treatment of 2 mol of the bowl-shaped tetrol 1 (derived originally from resorcinol and dihydrocinnamaldehyde) with 3 mol of TsO(CH₂)₄OTs gave diol 2. Eight compounds with different combinations of bridges were formed from 2 by treatment with Cs₂CO₃ and the following reagents in the presence of potential guests to give either free or complexed hemicarcerands as follows: ClCH₂Br gave 4; TsO(CH₂)₂OTs gave 5; TsO(CH₂)₃OTs gave 6; MsO(CH₂)₄OMs gave 7, a known system; MsO(CH₂)₅OMs gave 8; 2,3-bis(bromomethyl)quinoxaline gave 9; 1,3-(ClCH₂)₂C₆H₄ gave 10; 2,6-bis(chloromethyl)pyridine gave 11. Thirty-six fully characterized new hemicarceplexes are reported which were prepared either directly from diol 2 by the "sealing in" of the guest during introduction of the fourth bridge, or by guest exchange driven by mass law at 25 to 160 °C. The guests ranged in size from CHCl₃ to 1,2,3-(MeO)₃C₆H₃. The incarcerated guests correlated with portal sizes of their hosts. Crystal structures of 8⊙4-MeC₆H₄OMe and 10⊙CHCl₃ were determined. Changes in chemical shifts in ¹H NMR spectra of incarcerated and free guests are interpreted in terms of their locations in the hosts' inner phases. The length and nature of the unique host bridge affects the chemical shifts of the other bridges. Force field calculations of structural models for N-methylpyrrolidinone incarcerated in 4-7 were made. Approximate half-lives for decomplexation were determined for complexes involving the larger hosts and guests. Force-field calculations were made of binding energies and activation energies for decomplexations of models of 7⊙N-methylpyrrolidinone, 80⊙N-methylpyrrolidinone, and 10⊙N-methylpyrrolidinone. The activation energies for decomplexation were dissected into intrinsic and constrictive components.