Host-Guest Complexation. 33. Search for New Chiral Hosts

Article abstract of DOI:10.1021/jo00209a026

Nine new macrocyclic hosts have been designed, synthesized, and examined for their ability to bind alkali metal, ammonium, and alkylammonium cations.Their ring sizes vary from 17- to 24-membered.Five contain axially chiral units, three of which have not previously been incorporated in a host.Their structures are indicated by line formulas in which sequences of letters indicate the units and their points of attachment through which they are incorporated into the macroring.The order of the letters indicates the order of attachment of the units to one another.Chart I identifies the structures associated with the letters and Chart II identifies the structures of hosts 1-9 with the line formulas.The yields in the critical ring-closing reactions ranged from 5percent to 80percent.Additionally, Chart II also lists five assemblies of units (10-14) potentially useful for other host syntheses.Of these, 10 and 11 are chiral due to inhibition of ring inversion, whereas 14 is chiral due to the axial dissymmetry of the binaphthyl unit (B).Attempts to couple in two places 2 mol each of 12, 13, and 14 failed.The free energies (-ΔG^o values) in CDCl3 at 25 deg C of hosts 1-9 binding the picrate salts of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH4⁺, CH3NH3⁺, and t-BuNH3⁺ were measured.The -ΔG^o values were correlated with the structures of host and guests.