Supramolecular method for the determination of absolute configuration of chiral compounds: theoretical derivatization and a demonstration for a phenolic crown ether-2-amino-1-ethanol system.

A combination of anisotropic shielding effect and temperature dependence of NMR chemical shifts makes it possible to develop a supramolecular method for determination of absolute configuration of chiral compounds. The concept, theoretical derivatization, and first demonstration of this daedal noncovalent method using a host-guest system is described. This noncovalent method requires only three substrate solutions and can in principle be applied to any host-guest systems that follow the van't Hoff relation and have a clear anisotropic shielding effect based on a well-defined complex structure regardless of the extent of enantiomer selectivity.

m-Diethynylbenzene macrocycles: syntheses and self-association behavior in solution.

m-Diethynylbenzene macrocycles (DBMs), buta-1,3-diyne-bridged [4(n)]metacyclophanes, have been synthesized and their self-association behaviors in solution were investigated. Cyclic tetramers, hexamers, and octamers of DBMs having exo-annular octyl, hexadecyl, and 3,6,9-trioxadecyl ester groups were prepared by intermolecular oxidative coupling of dimer units or intramolecular cyclization of the corresponding open-chain oligomers. The aggregation properties were investigated by two methods, the (1)H NMR spectra and the vapor pressure osmometry (VPO). Although some discrepancies were observed between the association constants obtained from the two methods, the qualitative view was consistent with each other. The analysis of self-aggregation by VPO revealed unique aggregation behavior of DBMs in acetone and toluene, which was not elucidated by the NMR method. Namely, the association constants for infinite association are several times larger than the dimerization constant, suggesting that the aggregation is enhanced by the formation of dimers (a nucleation mechanism). In polar solvents, DBMs aggregate more strongly than in chloroform due to the solvophobic interactions between the macrocyclic framework and the solvents. Moreover, DBMs self-associate in aromatic solvents such as toluene and o-xylene more readily than in chloroform. In particular, the hexameric DBM having a large macrocyclic cavity exhibits extremely large association constants in aromatic solvents. By comparing the aggregation properties of DBMs with the corresponding acyclic oligomers, the effect of the macrocyclic structure on the aggregation propensity was clarified. Finally, it turned out that DBMs tend to aggregate more readily than the corresponding phenylacetylene macrocycles, acetylene-bridged [2(n)]metacyclophanes, owing to the withdrawal of the electron density from the aromatic rings by the butadiyne linkages which facilitates pi-pi stacking interactions.

Novel Self-Assembly of m-Xylylene Type Dithioureas by Head-to-Tail Hydrogen Bonding.

Dithiourea 1a self-assembles to form an orthogonal dimer structure both in solution and in the solid state, wherein the four thiourea groups establish a closed network of hydrogen bonds through a head-to-tail binding mode. This novel dimer structure was elucidated on the basis of (1)H NMR spectra, vapor pressure osmometry, and X-ray crystal structure analysis. Furthermore, a series of m-xylylene type dithioureas were synthesized and their dimerization constants (K(a)) in CDCl(3) were determined by dilution experiments using (1)H NMR spectroscopy. The magnitude of the K(a) values are dependent on the steric bulk of the side chains, the acidity of the thiourea groups, and the weak intermolecular interaction between the benzene rings of the side chains and the m-xylylene spacer.

Synthesis and Association Behavior of [4.4.4.4.4.4]Metacyclophanedodecayne Derivatives with Interior Binding Groups.

Intriguing association behavior in solution is exhibited by the rigid macrocycle 1. For instance, it reacts with organic cations to give ternary complexes of the composition (1⋅cation)⋅1, and with analogous macrocycles without cyano groups it forms heteroaggregates. R=CO2 C8 H17 .